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Script Grammar

Rule Script

The Script rule defines the logical entry point into Tremor's expression oriented scripting language. The scripting langauge can be embedded into queries via the script operator. The scripting language is also used to specify configuration of connectors, pipelines, flows, and operators in the query language.

A legal script is composed of:

  • An optional set of module comments
  • A sequence of top level expressions. There must be at least one defined.
  • An optional end of stream token

Scripting Language Entrypoint

This is the top level of the tremor scripting language tremor

Script

rule Script ::=
( ModComment ) ? TopLevelExprs
;

Type system

Tremor supports a data oriented or value based type system with a syntax that is backwards compatible with JSON.

Any well-formed and legal JSON document is a valid literal in tremor.

Tremor literals for null, boolean, string ( utf-8 ), integer ( 64-bit unsigned ), float ( 64-bit ieee ), arrays, and records are equivalent to their JSON counterparts.

Tremor also supports a binary literal for transporting and processing opaque binary data.

Asymmetric

JSON literals are valid tremor value literals.

Tremor literals MAY NOT always be valid JSON literal.

# The following literal is valid JSON and valid Tremor
[1, "snot", {}];

# The following literal is valid in tremor only
[1, "snot", {}, << data/binary >>, ];

Tremor supports comments, JSON does not. Tremor supports trailing commas in arrays and records, JSON does not. Tremor supports binary literal data, JSON does not.

Note: By default, most connectors in tremor serialize to and from json via a codec. The type system in tremor however is agnostic to the wire format of data that flows through tremor. So data originate as json, as msgpack.

Computations

Tremor also supports a rich expression language with the same support for additive, mutliplicate, comparitive, and logical unary and binary expressions as languages like rust and java.

As most of the data that flows through tremor is heirarchically structured or JSON-like tremor also has rich primitives for structural pattern matching, structural comprehension or iterating over data structures.

Loops

Tremor does not support while loop or other primitives that can loop, recurse or iterate indefinitely.

In an event based system, events are streaming continuously - so infinite loops that can block streams from making forward progress are considered harmful.

There are no loops.

We do support iteration over finite arrays.

We do support depth-limited tail recursive functional programming.

Expression oriented

The script processing is expression oriented. This is to say that every structural form supported by tremor returns a data structure as a result.

Event oriented

Scripts in tremor can emit or drop an `event that is being processed.

The event keyword is the subject. It identifies the value currently being processed.

The emit keyword halts processing succesfully with a value.

The drop keyword halts processing by discarding the current event.

Illustrative example

# Propagate events marked as important and convert them to system alerts
match event of
case %{ present important } => { "alert": event.message }
default => drop
end;

Rule ModComment

The ModComment rule specifies module comments in tremor.

Documentation comments for modules are optional.

A module documentation comment begins with a ### triple-hash and they are line delimited.

Muliple successive comments are coalesced together to form a complete comment.

The content of a module documentation comment is markdown syntax.

ModComment

rule ModComment ::=
'<mod-comment>'
| ModComment '<mod-comment>'
;

Example

Module level comments are used throughout the tremor standard library and used as part of our document generation process.

Here is a modified snippet from the standard library to illustrate

### The tremor language standard library it provides the following modules:
###
### * [array](std/array.md) - functions to deal with arrays (`[]`)
### * [base64](std/base64.md) - functions for base64 en and decoding
### * [binary](std/base64.md) - functions to deal with binary data (`<< 1, 2, 3 >>`)
### * [float](std/float.md) - functions to deal with floating point numbers
### * [integer](std/integer.md) - functions to deal with integer numbers
### * [json](std/json.md) - functions to deal with JSON
...

Rule TopLevelExprs

The TopLevelExprs rule defines semi-colon separated sequence of top level tremor expressions with an optional terminating semi-colon

TopLevelExprs

rule TopLevelExprs ::=
TopLevelExpr ';' TopLevelExprs
| TopLevelExpr ';' ?
;

The ToplEvelExprs specifies the expressions that are legal at the top level of a script expression.

script
event.sum * 2
end

A sequence of ';' semi-colon delimited expressions of the following form are permissible:

  • Constants
  • Function definitions
  • Intrinsic function definitions in the standard library
    • Provided by the runtime to document builtins - not user modifiable without a pull request or feature enhancement
  • Arbitrary complex expressions
  • Use definitions

Rule TopLevelExpr

The TopLevelExpr rule specifies the expression forms that are legal at the outer most scope of a tremor script definition.

The legal forms are:

  • Use declarations - these allow external modules to be referenced.
  • Constant expressions - these are immutable compile time constants.
  • Function definitions - these are user defined functions.
  • Intrinsic function definitions - these are builtin funtions provided by the runtime.

TopLevelExpr

rule TopLevelExpr ::=
Const
| FnDefn
| Intrinsic
| Expr
| Use
;

Example

In the tremor standard library many of the top level expressions are use definitions importing sub modules from the module path.

use std::array;     # Import the std array utilities
use std::base64 # Import the std base64 utilities;
use std::binary; # ...
use std::float;
use std::integer;
use std::json;

Rule InnerExprs

The InnerExprs rule defines the expression forms permissible within another containing scope. Like TopLevelExprs, inner expressions are separated by semi-colons. The semi-colon is optional for the last expression in a set of expressions.

At least one expression MUST be provided.

InnerExprs

rule InnerExprs ::=
Expr ';' InnerExprs
| Expr ';' ?
;

Example

The following basic forms are permissible

for event.object of case (k, v) => v end;
for event.list of case (i, e) => e end;
match event of case %{} => "record" default => "not a record" end;
let list = event.list;
drop;
"any literal or basic expression";
1 + 2 * 3;
emit {"snot": "badger" }
# ...

Rule Expr

The Expr rule aliases the SimpleExpr rule.

The alias allows higher levels of the DSL such as the rules in the deployment or query language to avoid some of the internal complexity in the scripting language.

Within the scripting DSLs grammar the different forms and variations of expression are significant.

However, in the higher level we limit exposure to a subset of these forms. This is done for convenience, and for consistency of usage, and ease of learning the language.

Expr

rule Expr ::=
SimpleExpr
;

The effective root of the subset of the expression langauge applicable in most processing context in tremor is captured by this rule.

Rule Const

The Const rule defines a rule that binds an immutable expression to an identifier.

As the value cannot be changed at runtime.

Const

rule Const ::=
( DocComment ) ? 'const' Ident '=' ComplexExprImut
;

How do I create new immutable constant variable in tremor?

use std::base64;
const snot = "snot";
const badger = "badger";
const snot_badger = { "#{snot}": "#{base64::encode(badger)}" };

Rule FnDefn

The FnDefn rule allows user defined functions to be defined.

This rule allows tremor users to create functions for reuse in one or many tremor applications.

FnDefn

rule FnDefn ::=
( DocComment ) ? 'fn' Ident '(' '.' '.' '.' ')' 'with' InnerExprs 'end'
| ( DocComment ) ? 'fn' Ident '(' FnArgs ',' '.' '.' '.' ')' 'with' InnerExprs 'end'
| ( DocComment ) ? 'fn' Ident '(' ')' 'with' InnerExprs 'end'
| ( DocComment ) ? 'fn' Ident '(' FnArgs ')' 'with' InnerExprs 'end'
| ( DocComment ) ? 'fn' Ident '(' ')' 'of' FnCases 'end'
| ( DocComment ) ? 'fn' Ident '(' FnArgs ')' 'of' FnCases 'end'
;

Pattern match based function arguments

Functions defined with an of keyword in their signature use pattern matching against arguments

fn fib_(a, b, n) of
case (a, b, n) when n > 0 => recur(b, a + b, n - 1)
default => a
end;

Ordinary functions

Functions defined with a with keyword in their signature use ordinary arity based matching.

fn fib(n) with
fib_(0, 1, n)
end;

Function documentation

In modular functions, it is customary to provide user level documentation for the intended users of a function. Here is an example from the tremor standard library

### Trace Identifiers
###
###

use std::type;
use std::binary;
use std::array;
use std::string;

## Is the `trace_id` valid
##
## Checks the `trace_id` argument to see if it is a valid
## trace id. A legal trace id is one of:
##
## * An array of integers in the range of [0..=255] of length 8
## * A binary 16 byte value
## * A 32-byte hex-encoded string
## * An array of 16 int values
## * Regardless of representation, the value must not be all zeroes
##
## Returns a record when the representation is well-formed of the form:
##
## ```tremor
## {
## "kind": "string"|"binary"|"array", # Depends on input
## "valid": true|false, # True if well-formed and valid
## "value": "<trace_id>" # Representation depends on `kind`
## }
## ```
##
## Returns an empty record `{}` when the representation not well-formed
##
fn is_valid(trace_id) of
# String representation
case(trace_id) when type::is_string(trace_id) =>
{ "kind": "string", "valid": trace_id != "00000000000000000000000000000000" and string::bytes(trace_id) == 32, "value": trace_id }
# Binary representation
case(trace_id) when type::is_binary(trace_id) =>
let arr = binary::into_bytes(trace_id);
{ "kind": "binary", "valid": binary::len(arr) == 16 and trace_id != << 0:64, 0:64 >>, "value": trace_id }
# Array representation
case(trace_id) when type::is_array(trace_id) =>
{ "kind": "array", "valid": array::len(arr) == 16 and trace_id != [ 0, 0, 0, 0, 0, 0, 0, 0], "value": trace_id }
default =>
false
end

Rule Intrinsic

The intrinsic rule defines intrinsic function signatures.

This rule allows tremor maintainers to document the builtin functions implemented as native rust code. The facility also allows document generation tools to document builtin intrinsic functions in the same way as user defined functions.

In short, these can be thought of as runtime provided.

For information on how to define user defined functions see the function rule.

Intrinsic

rule Intrinsic ::=
( DocComment ) ? 'intrinsic' 'fn' Ident '(' ')' 'as' ModularTarget
| ( DocComment ) ? 'intrinsic' 'fn' Ident '(' FnArgs ')' 'as' ModularTarget
| ( DocComment ) ? 'intrinsic' 'fn' Ident '(' FnArgs ',' '.' '.' '.' ')' 'as' ModularTarget
| ( DocComment ) ? 'intrinsic' 'fn' Ident '(' '.' '.' '.' ')' 'as' ModularTarget
;

Example

From our standard library generated documentation, we can see that the base64 encode function is an intrinsic function.

## Encodes a `binary` as a base64 encoded string
##
## Returns a `string`
intrinsic fn encode(input) as base64::encode;

Rule Use

Imports definitions from an external source for use in the current source file.

The contents of a source file form a module.

TREMOR_PATH

The TREMOR_PATH environment path variable is a : delimited set of paths.

Each path is an absolute or relative path to a directory.

When using relative paths - these are relative to the working directory where the tremor executable is executed from.

The tremor standard library MUST be added to the path to be accessible to scripts.

Use

rule Use ::=
'use' ModularTarget
| 'use' ModularTarget 'as' Ident
;

Modules

Modules can be scripts. Scripts can store function and constant definitions.

Scripts are stored in .tremor files.

Modules can be queries. Queries can store window, pipeline, script and operator definitions.

Scripts are stored in .trickle files.

Modules can be deployments. Deployments can store connector, pipeline and flow definitions.

Deployments are stored in .troy files.

Conditioning

Modules in tremor are resolved via the TREMOR_PATH environment variable. The variable can refer to multiple directory paths, each separated by a : colon. The relative directory structure and base file name of the source file form the relative module path.

Constraints

It is not recommended to have overlapping or shared directories across the set of paths provided in the tremor path.

It is not recommended to have multiple definitions mapping to the same identifier.

Rule DocComment

The DocComment rule specifies documentation comments in tremor.

Documentation comments are optional.

A documentation comment begins with a ## double-hash and they are line delimited.

Muliple successive comments are coalesced together to form a complete comment.

The content of a documentation comment is markdown syntax.

DocComment

rule DocComment ::=
'<doc-comment>'
| DocComment '<doc-comment>'
;

Example

Documentation level comments are used throughout the tremor standard library and used as part of our document generation process.

Here is a modified snippet from the standard library to illustrate

## Returns the instance of tremor.
##
## Returns a `string`
intrinsic fn instance() as system::instance;
...

This is a builtin function implemented in rust and used in a script as follows:

use tremor::system;

system::instance()

Rule Ident

An Ident is an identifier - a user defined name for a tremor value.

Ident

rule Ident ::=
'<ident>'
;

Examples of identifiers

let snot = { "snot": "badger" };

Keyword escaping

Surrounding an identifier with a tick '`' allows keywords in tremor's DSLs to be escaped

let `let` = 1234.5;

Emoji

You can even use emoji as identifiers via the escaping mechanism.

let `🚀` = "rocket";

But we cannot think of any good reason to do so!

Rule ComplexExprImut

The ComplexExprImut rule defines complex immutable expression in tremor.

ComplexExprImut

rule ComplexExprImut ::=
MatchImut
| ForImut
| ExprImut
;

Rule SimpleExpr

The SimpleExpr rule defines all the structural and simple expressions and literals in tremor.

SimpleExpr

rule SimpleExpr ::=
Match
| For
| Let
| Drop
| Emit
| ExprImut
;

Structural expressions

  • Match
  • For

Assignment

  • Let

Flow

  • Emit
  • Drop

Basic expressions

Binary, unary and literal expressions

Rule Match

The Match rule defines a mutable match statement in tremor.

Match

rule Match ::=
'match' ComplexExprImut 'of' Predicates 'end'
;

An illustration of the rule is a set of case statements, followed by an optional default case

  match event of
case %{} => "I am a possibly non-empty record",
case %[] => "I am a possibly non-empty array",
case %( "snot" ) => "I am a list with 1 element which is the string \"snot\"
default => "I'm something else"
end

Rule For

The For rule defines an mutable for comprehension.

For

rule For ::=
'for' ComplexExprImut 'of' ForCaseClauses 'end'
;

An illustration of the rule is a set of case statements, followed by an optional default case

  for event of
## Cases
end

The ForCaseClause rule has examples of the two basic forms for record and array comprehensions.

Rule Let

The Let rule allows an expression to be bound to a Path.

The Path references the subject of the assignment based on tremor's Path rules.

The bound Path is mutable.

Let

rule Let ::=
'let' Assignment
;

How do i create a local mutable variable in tremor?

let my_var = "this is a string";

Rule Drop

Drop halts event processing for the current event being processed returning control to the tremor runtime, dropping the event.

Constraints

The drop operation should be used with care as the in-flight event is discarded by the runtime. Where circuit breakers, guaranteed delivery and quality of service operations are being managed by the engine downstream these should be carefully programmed so that drop operations have no side-effects on non-functional behaviours of the tremor runtime.

Here be dragons!

Drop

rule Drop ::=
'drop'
;

define script boring
script
drop
end;
create script boring;
select event from in into boring;
select event from boring into out;

Drop signals to the tremor runtime that an event is not interesting and can be dropped without any further handling by the engine. Drop statements in a script or query result in the processing of the current event halting without any further action bye the tremor runtime.

The dropped event is discarded by the engine.

Rule Emit

Emit halts event processing for the current event being processed returning control to the tremor runtime, emitting a synthetic event as output.

By default, the emit operation will emit events to the standard output port out.

The operation can be redirected to an alternate output port.

Emit

rule Emit ::=
'emit' ComplexExprImut '=>' StringLiteral
| 'emit' ComplexExprImut
| 'emit' '=>' StringLiteral
| 'emit'
;

define script route
script
emit => "not_out"
end;

create script route;
select event from in into route;
select event from route/not_out into out;

Emit signals to the tremor runtime that an event has been processed fully and processing can stop at the point emit is invoked and a synthetic value returned without any further processing.

The emitted event is forwarded by the engine.

Rule ExprImut

The ExprImut is the root of immutable expressions in tremor.

ExprImut

rule ExprImut ::=
OrExprImut
;

The effective root of the subset of the expression langauge applicable in most immutable processing context in tremor is captured by this rule.

Rule AlwaysImutExpr

The AlwaysImutExpr defines the immutable expression forms in tremor.

Immutable expressions can be reduced at compile time and folded into literals.

AlwaysImutExpr

rule AlwaysImutExpr ::=
Patch
| Merge
| Invoke
| Literal
| Path
| Record
| List
| StringLiteral
| BytesLiteral
| Recur
;

Rule Patch

The Patch rule defines the patch statement in tremor.

Patch

rule Patch ::=
'patch' ComplexExprImut 'of' PatchOperations 'end'
;

Patch insert a field in a record

let a = patch event of
insert "test" => 1
end;

Default patch templates

patch event of
default => {"snot": {"badger": "goose"}}
end



## Rule Merge

The `Merge` rule defines a merge operation of two complex immutable expressions.



![Merge](svg/merge.svg)

```ebnf
rule Merge ::=
'merge' ComplexExprImut 'of' ComplexExprImut 'end'
;

How do I merge two two records?

merge {"a": 1, "b": 2, "c": 3 } of
{ "b": "bravo", "c": "charlie", "d": "delta" }
end;

The merge expression loosely follows the semantics of RFC 7396 - JSON Merge Patch.

From our example:

  • The field a is not patched and preserved
  • The field b is patched with the value bravo - the original value is replaced
  • The field d is not in the original, and is added.

The expression is useful when one record with another.

An alternative to the Merge expression is the Patch expression which is operation rather than value based.

Rule Invoke

The Invoke rule specifies the syntax of a function invocation.

Invoke

rule Invoke ::=
FunctionName '(' InvokeArgs ')'
| FunctionName '(' ')'
;

use std::string;

string::len("snot")

Rule Literal

The Literal rule defines the set of primitive literals supported in tremor.

Literal

rule Literal ::=
Nil
| Bool
| Int
| Float
;

Primitive literal types in tremor are integer, floating point, boolean and the null reference.

String literals are UTF-8 encoded values and support interpolation with single line ( regular ) and multi line ( heredoc style ) variant forms.

Rule Path

The Path rule defines path operations over expressions.

Path operations structures to be tersely indexed in a path like structure.

Path operations are supported on

  • A subset of expressions ( record, array, function )
  • Meta keywords like $, args, state, event, group, window

Path

rule Path ::=
MetaPath
| EventPath
| StatePath
| LocalPath
| ConstPath
| AggrPath
| ArgsPath
| ExprPath
;

Path expressions are how events and in memory state in tremor are referenced in scripts.

How to reference metadata

The tremor runtime can provide and consume metadata with the events being processed by the runtime.

Metadata is distinguished by a $ dollar sign

let foo = $request # The local path `foo` is a copy of the metadata `$request`

Connectors such as kafka and http can generate metadata that scripts, queries and pipelines can manipulate and process to tune tremor's runtime behaviour.

How to reference the current streaming event

The current event streaming through tremor in the current pipeline will be available to queries, logics and scripts via the event keyword.

The event keyword can be further dereferenced via path statements

# Where event is a record
let foo = event.snot; # The local path `foo` is a copy of the `snot` field from the current event
# Where event is an array
let foo = event[10]; The local path `foo` is a copy of the 10th element of the current event.

How to reference pipeline state

Scripts in tremor can store state that is available for the lifetime of a pipeline via the state keyword.

The state keyword can be further dereferenced via path statements

# Where state is a record
let foo = state.snot; # The local path `foo` is a copy of the `snot` field from the state record
# Where state is an array
let foo = state[10]; The local path `foo` is a copy of the 10th element of the state array

### How to reference arguments

For operators and structures that support arguments the `args` keyword can be
used to dereference values via path statements.

```tremor
# Where state is a record
let foo = args.snot; # The local path `foo` is a copy of the `snot` field from the args record

Args are nominal and always record values in tremor.

How can window state be referenced

Operations supporting windows and groups can dereference the cached state via the window and group keywords which both support path operations.

Rule Record

The Record rule defines a set of name-value pairs delimited by , a comma.

Records are enclosed in { and } curly braces.

The record structure in tremor is backwards compatible with JSON.

All JSON records can be read by tremor.

Not all tremor records can be read by a JSON reader as tremor supports computations, comments and trailiing , commas in its record and array structures.

Record

rule Record ::=
'{' Fields '}'
| '{' '}'
;

How are literal records or map types or key-value collections defined in tremor?

We use { .. } squigly braces to delimit record -like data.

Can records be nested?

Record values can be any valid primitive of structural type supported by tremor, including other records.

Does tremor support typed records?

No. A record in tremor can have element values from any supported primitive or structural type in tremor.

Validation that a record conforms to a shape, schema or structure can be achieved through match expressions.

use std::type;

let bad = { "list-of-bool": [true, false, "snot"] };
let good = { "list-of-bool": [true, false ], "flag": true };

fn list_of_bool(l) with
let valid = true;
for l of
case (i,e) when type::is_bool(e) and valid == true => let valid = true
case (i, otherwise) => let valid = false
end;
valid # return true if list is all bool, false otherwise
end;

fn is_good_record(r) with
let valid = false;
match r of
case extract=%{ present flag, list-of-bool ~= %[] }
when list_of_bool(extract["list-of-bool"]) =>
let valid = true
default =>
let valid = false
end;
valid
end;

is_good_record(bad); # should fail
is_good_record(good); # should succeed

This user defined function can then be used in guard clauses like when type::is_bool(e) ... in the example code.

Rule List

The List rule defines a [ and ] square bracket delimited sequence of zero or many ',' delimited expressions.

List

rule List ::=
'[' ListElements ']'
| '[' ']'
;

How are literal array or list or vectorc data collections defined in tremor?

We use [ .. ] square brackets to delimit list-like data.

Are multi-dimensional arrays supported?

Multi-dimensional arrays are compositional and can be nested

Does tremor support typed lists?

No. A list in tremor can have elements from any supported primitive or structural type.

Validation that a list is for a single type - such as a list of boolean values can be defined as follows:

use std::type;

let bad = [true, false, "snot"];
let good = [true, false ];

fn list_of_bool(l) with
let valid = true;
for l of
case (i,e) when type::is_bool(e) and valid == true => let valid = true
case (i, otherwise) => let valid = false
end;
valid # return true if list is all bool, false otherwise
end;

list_of_bool(bad); # should fail
list_of_bool(good); # should succeed

This user defined function can then be used in guard clauses like when type::is_bool(e) ... in the example code.

Rule StringLiteral

The StringLiteral rule defines a string literal in tremor.

Strings are " single-quote or """ triple-quote delimited blocks of UTF-8 text.

A single-quote string is a single line string, supporting sting interpolation.

A triple-quote string is a multi-line string, supporting sting interpolation.

StringLiteral

rule StringLiteral ::=
'heredoc_start' StrLitElements 'heredoc_end'
| '\\' StrLitElements '\\'
| '\\' '\\'
;

How do I define single line string literals?

A single line string MUST be on a single line with raw newline characters ( unless escaped ).

"I am a literal string"

How do i define multi line string literals?

A multi line string MUST span multiple lines with raw newline characters.

Multi line strings

"""
I am a
multi
line
string
"""

The following example is a malformed multi line string:

""" snot """

Which when executed will result in a compile time error:

Error:
1 | """ snot """
| ^^^ It looks like you have characters tailing the here doc opening, it needs to be followed by a newline

Simple and nested Interpolation

Strings in tremor can be interpolated with internal scripts

"""

I am an #{interpolated} #{event.sum / event.count} string

Interpolations can be simple, as above, or #{
merge event of
{ "#{snot}": """

#{badger * 1000 + crazy_snake }

""" }
}
"""

This will result in the output:

"\nI am an interpolated 5.0 string\n\nInterpolations can be simple, as above, or {\"sum\":10,\"count\":2,\"snot\":\"\\n    20001\\n\\n    \"}\n"

Note that the merge operation merges an event { "sum": 10, "count": 10 } with in scope values of snot that evaluates to the literal string "snot" and the numerics badger ( 20 ) and crazy_snake ( 1 ). Interpolations are nestable and field names or any other string literal in tremor can be interpolated.

However, we do not recommend complex nested interpolated strings. Defining a function and calling it may be a better alternative for most applications and uses.

Rule BytesLiteral

The BytesLiteral is a representation of opaque binary data literals in tremor

The syntax is a subset of the bit syntax representation in the Erlang Programming Language.

We ❤️ Erlang.

We ❤️ bit syntax!

BytesLiteral

rule BytesLiteral ::=
'<<' '>>'
| '<<' Bytes '>>'
;

Examples

# Import standard tremor binary utility functions
use std::binary;

# Structure of a TCP packet header
# 0 1 2 3
# 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | Source Port | Destination Port |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | Sequence Number |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | Acknowledgment Number |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | Offset| Res. | Flags | Window |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | Checksum | Urgent Pointer |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | Options | Padding |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# |
# Data section proceeding packet header is optional and may or |
# it is up to the user whether or not to include this in a |
# binary literal or not |
# |
# . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .|

# Record representation of a TCP packet
let event = {
"src": {"port": 1234},
"dst": {"port": 2345},
"seq": event,
"ack": 4567,
"offset": 1,
"res": 2,
"flags": 3,
"win": 4,
"checksum": 5,
"urgent": 6,
"data": "snot badger!" # For encoding we
};

# Convert the record into a binary encoded TCP packet
binary::into_bytes(<<
# Header segment
event.src.port:16, event.dst.port:16,
event.seq:32,
event.ack:32,
event.offset:4, event.res:4, event.flags:8, event.win:16,
event.checksum:16, event.urgent:16,
# Data segment
event.data/binary
>>)

Rule Recur

The Recur rule defines stack-depth-limited tail-recursion in tremor functions.

Recur

rule Recur ::=
'recur' '(' ')'
| 'recur' '(' InvokeArgs ')'
;

fn fib_(a, b, n) of
case (a, b, n) when n > 0 => recur(b, a + b, n - 1)
default => a
end;

fn fib(n) with
fib_(0, 1, n)
end;

Tremor's functional programming langauge supports tail recursion via the recur keyword. Tail recursion in tremor is limited to a fixed stack depth - infinite recursion is not permissible.

Rule InvokeArgs

The InvokeArgs rule defines a sequence of expression statements.

InvokeArgs

rule InvokeArgs ::=
InvokeArgs_
;

A comma delimited sequence of complex expressions

Rule OrExprImut

The OrExprImut rule supports logical or expressions in tremor.

Binary logical or expressions take precedence over logical exclusive or expressions.

OrExprImut

rule OrExprImut ::=
BinOp!(BinOr, ExprImut, XorExprImut)
| XorExprImut
;

let example = a or (b & 0);

Rule BinOr

The BinOr rule defines binary or operation

OperatorDescription
xorBinary or

BinOr

rule BinOr ::=
'or'
;

Logical OR

false or false  # false

false or true # true

true or false # true

true or true # true

Rule XorExprImut

The XorExprImut rule supports logical exclusive or expressions in tremor.

Binary logical exclusive or expressions take precedence over logical and expressions.

XorExprImut

rule XorExprImut ::=
BinOp!(BinXor, XorExprImut, AndExprImut)
| AndExprImut
;

let example = a ^ (b & 0);

Rule BinXor

The BinXor rule defines binary exclusive or operation

OperatorDescription
xorBinary exlusive or

BinXor

rule BinXor ::=
'xor'
;

Logical Exclusive Or

    false xor false # false

false xor true # true

true xor false # true

true xor true # false

Rule AndExprImut

The AndExprImut rule supports logical and expressions in tremor.

Binary logical and expressions take precedence over bitwise or expressions.

AndExprImut

rule AndExprImut ::=
BinOp!(BinAnd, AndExprImut, BitOrExprImut)
| BitOrExprImut
;

x + y

Rule BinAnd

The BinAnd rule defines binary and operation

OperatorDescription
andBinary and

BinAnd

rule BinAnd ::=
'and'
;

Logical And

false and false   # false

false and true # false

true and false # false

true and true # true

Rule BitOrExprImut

The BitOrExprImut rule supports bitwise or expressions in tremor.

Binary bitwise or expressions take precedence over bitwise exclusive or expressions.

BitOrExprImut

rule BitOrExprImut ::=
BitXorExprImut
;

let example = a | (b & 0);

Rule BitXorExprImut

The BitXorExprImut rule supports bitwise exclusive or expressions in tremor.

Binary bitwise exclusive or expressions take precedence over bitwise and expressions.

BitXorExprImut

rule BitXorExprImut ::=
BinOp!(BinBitXor, BitXorExprImut, BitAndExprImut)
| BitAndExprImut
;

let example = a ^ (b & 0);

Rule BinBitXor

The BinBitXor rule defines binary bitwise exlusive-or operation

OperatorDescription
^Binary logical xor exclusive or

BinBitXor

rule BinBitXor ::=
'^'
;

Bitwise behaviour, when used with integers

  42 ^ 2    # 40
42 ^ -2 # -44
42 ^ 0 # 42
-42 ^ 2 # -44
-42 ^ -2 # 40

Logical behaviour, when used with boolean predicates

  true ^ true   # false
true ^ false # true

Rule BitAndExprImut

The BitAndExprImut rule supports bitwise and expressions in tremor.

Binary bitwise and expressions take precedence over equality expressions.

BitAndExprImut

rule BitAndExprImut ::=
BinOp!(BinBitAnd, BitAndExprImut, EqExprImut)
| EqExprImut
;

let example = a & (b & 0);

Rule BinBitAnd

The BinBitAnd rule defines binary bitwise and operation

OperatorDescription
&Binary logical and

BinBitAnd

rule BinBitAnd ::=
'&'
;

Bitwise behaviour, when used with integers

  42 & 2    # 2
42 & -2 # 42
42 & 0 # 0
-42 & 2 # 2
-42 & -2 # -42

Logical behaviour, when used with boolean predicates

  true & true   # true
false & true, # false

Rule EqExprImut

The EqExprImut rule supports equality expressions in tremor.

Binary equality expressions take precedence over comparitive expressions.

EqExprImut

rule EqExprImut ::=
BinOp!(BinEq, EqExprImut, CmpExprImut)
| CmpExprImut
;

let example = a == (b & 0);

Rule BinEq

The BinEq rule defines binary equality operations

OperatorDescription
==Binary equality
!=Binary non-equality

BinEq

rule BinEq ::=
'=='
| '!='
;

Are these values the same

let predicate = a == b

Are these values different

let predicate = a != b

Rule CmpExprImut

The CmpExprImut rule supports comparative expressions in tremor.

Binary comparative expressions take precedence over bit shift expressions.

CmpExprImut

rule CmpExprImut ::=
BinOp!(BinCmp, CmpExprImut, BitShiftExprImut)
| BitShiftExprImut
;

x > y

Rule BinCmp

The BinCmp rule defines binary comparitive operations

OperatorDescription
>=Binary greater than or equal to
>Binary greater than
<=Binary less than or equal to
<Binary less than

BinCmp

rule BinCmp ::=
'>='
| '>'
| '<='
| '<'
;

Is greater than

let predicate = a > b

Is greater than or or equal to

let predicate = a >= b

Is less than or equal to

let predicate = a <= b

Is less than

let predicate = a < b

Rule BitShiftExprImut

The BitShiftExprImut rule supports bit shift expressions in tremor.

Binary bit shift expressions take precedence over bitwise additive expressions.

BitShiftExprImut

rule BitShiftExprImut ::=
BinOp!(BinBitShift, BitShiftExprImut, AddExprImut)
| AddExprImut
;

let example = a >>> (b & 0);

Rule BinBitShift

The BinBitShift rule defines bit shift operations

OperatorDescription
>>>Binary bit shift right, unsigned
>>Binary bit shift right, signed
<<Binary bit shift left, signed

BinBitShift

rule BinBitShift ::=
'>>'
| '>>>'
| '<<'
;

[
"right bit shift (signed)",
42 >> 0, # 0
42 >> 2, # 10
-42 >> 2, # -11
42 >> 63, # 0

# right bit shift (signed) (invalid)
#42 >> 64,
#42 >> -1,
#42 >> 2.0,
#42 >> "2",
#42 >> true

"right bit shift (unsigned)",
42 >>> 0, # 42
42 >>> 2, # 10
-42 >>> 2, # 4611686018427387893
42 >>> 63, # 0

# right bit shift (unsigned) (invalid)
#42 >>> 64,
#42 >>> -1,
#42 >>> 2.0,
#42 >>> "2",
#42 >>> true

"left bit shift",
42 << 0, # 42
42 << 2, # 168
-42 << 2, # -168
42 << 63 # 0

# left bit shift (invalid)
#42 << 64
#a << 64
#42 << -1
#42 << 2.0
#42 << "2"
#a << "2"
#42 << true
#42 <<< 2
]

Rule AddExprImut

The AddExprImut rule supports additive expressions in tremor.

Binary additive expressions take precedence over multiplicative expressions.

AddExprImut

rule AddExprImut ::=
BinOp!(BinAdd, AddExprImut, MulExprImut)
| MulExprImut
;

x - y

Rule BinAdd

The BinAdd rule defines additive operations

OperatorDescription
+Binary addition
-Binary subtraction

Note that the + binary operation is also used for string concatenation.

BinAdd

rule BinAdd ::=
'+'
| '-'
;

Numeric addition

1 + 2 # Addition, if one operand is a float, the result will be a float

Numeric subtraction

1 - 2 # Subtraction, if one operand is a float, the result will be a float

Rule MulExprImut

The MulExprImut rule supports multiplicative expressions in tremor.

Binary multiplicative expressions take precedence over unary expressions.

MulExprImut

rule MulExprImut ::=
BinOp!(BinMul, MulExprImut, UnaryExprImut)
| UnaryExprImut
;

x * y

Rule BinMul

The BinMul rule defines multiplicative operations

OperatorDescription
*Binary multiplication
/Binary division
%Binary modulo

BinMul

rule BinMul ::=
'*'
| '/'
| '%'
;

Numeric multiplication

2 * 1.5 # multiplication, if any argument is floating point, result is floating point

Numeric division

2 / 1.5 # division, results is always a floating point value

Integer numeric Modulus

5  % 2 # modulus - operands must not integers

Rule UnaryExprImut

The UnaryExprImut rule specifies unary expression operations.

Expressions can be marked as + positive, - negative explicitly when needed.

Otherwise, the expression reduces to a simple unary expression.

The simple unary expression has lower precedence.

UnaryExprImut

rule UnaryExprImut ::=
'+' UnaryExprImut
| '-' UnaryExprImut
| UnarySimpleExprImut
;

Is the root expression for unary expressions in the language.

-(1)

Rule UnarySimpleExprImut

The UnarySimpleExprImut rule specifies predicate unary expression operations.

Expressions can be marked explicitly with not or ! to negate the target simple presence expression.

Otherwise, the expression reduces to a simple presence expression.

The simple presence expression has lower precedence.

UnarySimpleExprImut

rule UnarySimpleExprImut ::=
'not' UnarySimpleExprImut
| '!' UnarySimpleExprImut
| PresenceSimplExprImut
;

not (a and b)

Rule PresenceSimplExprImut

The PresenceSimplExprImut rule specifies presence and simple expressions

Expressions path predicate tests based on the present and absent predicate test expressions, or a simple expression.

Otherwise, the expression reduces to a simple expression.

The simple expression has lower precedence.

PresenceSimplExprImut

rule PresenceSimplExprImut ::=
'present' Path
| 'absent' Path
| SimpleExprImut
;

present $.request.method
absent state.cache

Rule SimpleExprImut

The SimpleExprImut rule defines optionally parenthesized simple immutable expressions in tremor.

SimpleExprImut

rule SimpleExprImut ::=
'(' ComplexExprImut ')'
| AlwaysImutExpr
;

A parenthetic or simple non-parenthetic expression

( 1 + 2 ) * 3;

Rule MatchImut

The MatchImut rule defines a match statement in tremor.

MatchImut

rule MatchImut ::=
'match' ComplexExprImut 'of' PredicatesImut 'end'
;

An illustration of the rule is a set of case statements, followed by an optional default case

  match event of
case %{} => "I am a possibly non-empty record",
case %[] => "I am a possibly non-empty array",
case %( "snot" ) => "I am a list with 1 element which is the string \"snot\"
default => "I'm something else"
end

Rule ForImut

The ForImut rule defines an immutable for comprehension.

ForImut

rule ForImut ::=
'for' ComplexExprImut 'of' ForCaseClausesImut 'end'
;

An illustration of the rule is a set of case statements, followed by an optional default case

  for event of
## Cases
end

The ForCaseClauseImut rule has examples of the two basic forms for record and array comprehensions.

Rule ModularTarget

A ModularTarget indexes into tremor's module path.

In tremor a module is a file on the file system.

A module is also a unit of compilation.

A ModularTarget is a :: double-colon delimited set of identifiers.

Leading :: are not supported in a modular target..

Trailing :: are not supported in a modular target.

ModularTarget

rule ModularTarget ::=
Ident
| ModPath '::' Ident
;

Examples

Loading and using a builtin function

# Load the base64 utilities
use std::base64;

# Base64 encode the current `event`.
base64::encode(event)

Loading and using a builtin function with an alias

# Load the base64 utilities
use std::base64 as snot;

# Base64 encode the current `event`.
snot::encode(event)

Rule FnArgs

The FnArgs rule defines , comma delimited arguments to a tremor function.

FnArgs

rule FnArgs ::=
Ident
| FnArgs ',' Ident
;

Rule FnCases

The FnCases rule defines a sequence of cases for structural pattern matching in tremor pattern functions.

FnCases

rule FnCases ::=
FnCaseClauses FnCaseDefault
| FnCaseDefault
;

connector/console/in

The connector console via its standard in port

Rule FnCaseClauses

The FnCaseClauses defines the case syntax to structurally matched function signatures in tremor.

FnCaseClauses

rule FnCaseClauses ::=
FnCase
| FnCaseClauses FnCase
;

Rule FnCaseDefault

The FnCaseDefines rule defines a default match clause for use in pattern match function signatures in tremor.

FnCaseDefault

rule FnCaseDefault ::=
'default' Effectors
;

Rule Effectors

The Effectors rule defines an effect block.

Effectors

rule Effectors ::=
'=>' Block
;

Example

An effector is an => arrow followed by Block sequence.

In many of the structural forms such as match, for or patch and effector is a sequence of logic that is executed when certain conditions occur. The final statement in an effector is the result of the sequence of executions.

As an example, here is a for compresension that enumerates a list and computes the stringified representation of the elements of the list.

The for expression collects each iterations result from the effector's block statement and aggregates them into a list.

for [1, 2, 3, 4, 5] of
case (i, e) => "#{e}";
end;

Rule FnCase

The FnCase rule defines an array predicate pattern supporting match clause for use in pattern match function signatures in tremor.

FnCase

rule FnCase ::=
'case' '(' ArrayPredicatePatterns ')' WhenClause Effectors
;

A case definition in a pattern match function definition

use std::type;

fn snottify(s) of
# Matches the literal string "badger"
case ("badger") => "snot badger, hell yea!"
# Matches any well formed json argument
case (~ json||) => let s.snot = true; s
# Matches any literal string
case (s) when type::is_string(s) => "snot #{s}"
# Matches, everything else
default => "snot caller, you can't snottify that!"
end;

Rule ArrayPredicatePatterns

The ArrayPredicatePatterns rule defines a set of comma delimited ArrayPredicatePattern rules.

ArrayPredicatePatterns

rule ArrayPredicatePatterns ::=
ArrayPredicatePatterns ',' ArrayPredicatePattern
| ArrayPredicatePattern
;

Rule WhenClause

The WhenClause rule defines an optional guard expression.

WhenClause

rule WhenClause ::=
( 'when' ComplexExprImut ) ?
;

Implicit guard

When no when clause is provided it is always executed equivalent to

when true

Explicit guards

Guards are predicate or boolean expressions, so any expression that reduces to a boolean result can be used in the WhenClause

when present state.snot and present event.badger

In the above rule, the state must be a record with a field snot present and the current event must be a record with a field badger present

Rule Nil

The Nil rule defines the syntax of the nil literal in tremor.

Nil

rule Nil ::=
'nil'
;

Example

null # The `null` literal value

Rule Bool

The Bool rule defines the syntax of boolean literal in tremor.

Bool

rule Bool ::=
'bool'
;

Example

true # The boolean `true` literal
false # The boolean `false` literal

Rule Int

The Int rule literal specifes the syntax of integer literals in tremor.

Int

rule Int ::=
'int'
;

Integer literals

Integer literals in tremor are 64 bit signed values of the form

1234

Values can be separated by an _ ( underscore ) for easy reading

let million = 1_000_000

Rule Float

The Float rule literal specifes the syntax of IEEE float literals in tremor.

Float

rule Float ::=
'float'
;

Floating point literals

Floating point literals in tremor are 64 bit signed IEEE floating point values of the form

1234.0e10

Values can be separated by an _ ( underscore ) for easy reading

let million = 1_000_000.1234e-5

Rule StrLitElements

The StrLitElements rule defines the internal structure of a string literal in tremor.

String literal in tremor support string interpolation via the #{ and } escape sequence. Content within the escape sequence can be any legal and valid tremor expression.

StrLitElements

rule StrLitElements ::=
StringPart StrLitElements
| '\\\\#' StrLitElements
| '#{' ExprImut '}' StrLitElements
| StringPart
| '\\\\#'
| '#{' ExprImut '}'
;

Inside a literal tremor string

A string literal in tremor is a composition of multiple segments or parts.

These can be composed of:

  • One or many single line string parts
  • One or many multi line string parts
  • A blackslash escaped \\# to escape interpolated syntax, optinally followed by more string literal parts
  • Or, a #{ .. } delimited interpolated section
    • Within an interpolated section there are no constraints on raw newline usage
    • For complex interpolated sections, prefer good indentation!

Rule StringPart

The StringPart rule defines a simple or heredoc style string part.

StringPart

rule StringPart ::=
'string'
| 'heredoc'
;

The " delimited string is single line

The """ delimited string is multi line

The forms can be mixed to construct a string literal

Interpolation is supported by both forms

Rule ListElements

The ListElements rule defines a , comma delimited sequence of expression elements.

ListElements

rule ListElements ::=
ListElements_
;

List literals

Unlike JSON, trailing commas are supported

[foo,] # A non empty list, a trailing comma is optionally permissible

Except in empty lists, where the idiomatic form is preferred:

[] # An empty list - no trailing comma here!

Rule ListElements_

The ListElements_ rule is internal to the ListElements rule.

The rule defines a sequence of , comma delimited expression elements using the Sep macro rule.

ListElements_

rule ListElements_ ::=
Sep!(ListElements_, ComplexExprImut, ",")
;

See ListElements rule for details.

This rule wraps away a lalrpop macro call for ease of reference in other rules in the grammar source.

Rule Fields

The Fields rule defines a set of comma delimited Field rules.

Fields

rule Fields ::=
Fields_
;

Example for record patterns

%{ present snot, badger == "badger", list = %[] }

Rule Field

The Field rule defines a : colon delimited name value pair for a record literal.

The name is a string literal.

The value is an expression.

Field

rule Field ::=
StringLiteral ':' ComplexExprImut
;

How do i define record fields?

The syntax is similar to JSON:

{ "field": "value" }

With the exception that fields may have an optional ',' terminal trailing comma

Interpolated field names

As literal strings in tremor support string interpolation the following variants are equivalent:

{ "snot": "badger" }

let snot = "snot";
{ "#{snot}": "badger" };

But, not all legal variations are recommended:

let snot = """
snot"""; # This may result in tears
{ "#{snot}": "badger" };

Another legal but likely not useful variation:

let snot = { "snot": "badger" };
{ "#{snot}": "badger" };

Will result in a stringifield json being encoded as the field name:

{"{\"snot\":\"badger\"}":"badger"}

Rule MetaPath

The MetaPath rule defines path operations for event metadata references.

In the context of a streaming event, allows metadata generated by the runtime to be accessed via path operations.

It is also possible to write to metadata to hint at the runtime to perform certain functions on the event data being forwarded. Tremor operators and connectors can read and write metadata.

MetaPath

rule MetaPath ::=
'$' Ident PathSegments
| '$' Ident
| '$'
;

How do i reference event metadata?

Events in tremor encapsulate data from other systems sent and received from tremor via configured connectors. Information about that data or metadata can also be provided by the runtime, and used in some operators and connectors to control tremor's runtime behaviour.

Meta-data is accessed via the $ dollar symbol.

let metadata = $;

Metadata can be any legal tremor value, but it is typically a record structure

let metastring = "snot" + $;

Meta-data can be written through via a let operation

let $command = { "do-things": "with-this-meta-request" }

Rule EventPath

The EventPath rule defines path operations for streaming events in tremor.

Allows the current streaming event to be dereferenced via path operations.

EventPath

rule EventPath ::=
'event' PathSegments
| 'event'
;

How do i dereference event data?

The current event is accessed via the event keyword.

The event can be any legal tremor value. If it is a record or an array, then it can be dereferenced via the path language in the usual way.

event.snot; # Event record, field 'snot'
let badger = event[0]; Event array, first element

Events can be mutated and manipulated and used as an output

select { "wrapped-event": event } from in into out;

Rule StatePath

The StatePath rule defines path operations for user defined in memory state in tremor.

Allows the state value to be dereferenced via path operations.

StatePath

rule StatePath ::=
'state' PathSegments
| 'state'
;

How do i reference state in tremor?

Tremor programs can be stateful in many ways - such as through the state managed by operators and windowed operations by the runtime on behalf of the user provided program.

The state keyword allows an arbitrary value controlled by a users program to be maintained and managed by the user program.

let my_state = state;

State can be written through via a let operation

let state = match state of
case null => { "count": 1 }
default => { "count"": state.count + 1 }
end;

Rule LocalPath

The LocalPath rule enables path operations on locally scoped identifiers.

LocalPath

rule LocalPath ::=
Ident PathSegments
| Ident
;

A local path is simply a path structure that is bounded to a locally defined value

let snot = { "snot": "badger" };

snot.snot # The field 'snot', on the local path reference 'snot'

Rule ConstPath

The ConstPath rule enables path operations on module scoped references.

ConstPath

rule ConstPath ::=
ModPath '::' LocalPath
;

A fully scoped path that does not include dynamic resolution or runtime type information.

Rule AggrPath

The AggrPath rule defines path operations for group and window references.

In the context of a windowed operation, enables the group and window meta keywords to partipcate in path operations.

AggrPath

rule AggrPath ::=
'group' PathSegments
| 'group'
| 'window' PathSegments
| 'window'
;

How do I reference the computed group dimension?

use std::record;
define window by_2 from tumbling
with
size = 2
end;

select {
"g": group[0], # Extract current group dimension
"c": aggr::stats::sum(event.c),
}
from in[by_2]
group by set(each(record::keys(event.g))) into out;

Rule ArgsPath

The ArgsPath rule defines path operations for args references.

ArgsPath

rule ArgsPath ::=
'args' PathSegments
| 'args'
;

How do i reference arguments?

Arguments are encapsualted via the args keyword symbol.

let what = args;

Arguments are always record structured

    1 | let args = 1;
| ^^^^^^^^ Can't assign to a constant expression

Arguments cannot be assigned to or overridden in scripts.

Rule ExprPath

The ExprPath rule defines path operations for expressions.

ExprPath

rule ExprPath ::=
ExprPathRoot PathSegments
;

Allows dereferencing literal values vi path expressions

{"snot": 0, "badger": 1, "goose": 2}["badger"];
{"snot": 0, "badger": 1, "goose": 2}.badger;

...

some_record_fn().record_field

Rule ExprPathRoot

The ExprPathRoot rule defines a subset of expressions where path operations are supported.

These are:

  • Record literals or references to records.
  • Array literals or references to arrays.
  • The result of function invocations.
  • The result of Parenthetic expressions.

ExprPathRoot

rule ExprPathRoot ::=
'(' ComplexExprImut ')'
| Invoke
| Record
| List
;

An internal rule to the ExprPath rule that defines legal roots for a dynamic path dereference.

Rule PathSegments

The PathSegments rule specifies the continuation of a path rule.

Form VariationDescription
.<Ident>A terminal segment dereferencing a record field
<Ident><PathSegments>A non-terminal segment dereferencing a record field
[<Selector>]A range or index segment dereferencing an array
[<Selector>]A terminal range or index segment dereferencing an array
[<Selector>]<PathSegments>A non-terminal range or index segment dereferencing an array

PathSegments

rule PathSegments ::=
'.' Ident PathSegments
| '[' Selector ']' PathSegments
| '[' Selector ']'
| '.' Ident
;

``tremor a.b a["b"] a[0..5]


Defines how structural values in tremor can be dereferenced to get at internal parts such as
an element of an array, or a field of a record.



## Rule ModPath

The `ModPath` rule defines a modular path.

A modular path is a sequence of `Ident`s separated by a `::` double-colon.



![ModPath](svg/modpath.svg)

```ebnf
rule ModPath ::=
ModPath '::' Ident
| Ident
;

How do i reference something from the standard library?

The standard library contains reusable constants, functions and other definitions that can be used in scripts via the Use and ModPath rules.

For example, if you have a file called foo.tremor in a src folder you can append this to your TREMOR_PATH environment variable

export TREMOR_PATH=/path/to/src

Assuming foo.tremor contains the following code:

fn meaning_of_life() of
42
end;

We can use this in another script as follows:

use foo;

let meaning = foo::meaning_of_life();

Rule Selector

The Selector rule specifies an index or range of an array.

A range is a : colon separated pair of expressions.

An index is a single expression.

Selector

rule Selector ::=
ComplexExprImut ':' ComplexExprImut
| ComplexExprImut
;

Field selection for records

Selecing a record field using array notation

let snot = badger["snot"]

Select the field 'snot' from the record 'badger'

Ordinal selection for arrays

let e = badger[0];

Select the 0th ( first ) element of the array 'badger'

Range selection for arrays

let e = badger[0:5];

Select the 0th up to but no including the 5th element of the array 'badger'

Rule FunctionName

The FunctionName rule defines a path to a function in tremor.

It can be an Ident for functions defined in local scope.

It can be a ModPath for functions in a modular scope.

FunctionName

rule FunctionName ::=
Ident
| ModPath '::' Ident
;

Rule InvokeArgs_

The InvokeArgs_ rule is an internal rule of the InvokeArgs rule.

The rule specifies a ; semi-colon delimited sequence of expression statements.

InvokeArgs_

rule InvokeArgs_ ::=
Sep!(InvokeArgs_, ComplexExprImut, ",")
;

See InvokeArgs rule for details.

This rule wraps away a lalrpop macro call for ease of reference in other rules in the grammar source.

Rule Assignment

The Assignment rule allows an expression to be bound to a Path.

The Path references the subject of the assignment based on tremor's Path rules.

Assignment

rule Assignment ::=
Path '=' SimpleExpr
;

The rule assigns an expression to a path by reference.

x = 2

Assigns x to the value literal 2

x.y = 2

Assigns the field y on record x to the value literal 2

Assignments expressions can be constant such as via the Const rule or mutable such as via the Let rule.

Rule PatchOperations

The PatchOperations rule defines a sequence of semi-colon delimited patch operations.

PatchOperations

rule PatchOperations ::=
PatchOperationClause
| PatchOperations ';' PatchOperationClause
;

A sequence of patch operations

Rule PatchOperationClause

The PatchOperationClause rule defines operations of a patch statement.

A patch operation can:

  • Insert, update, copy ( clone ), move ( rename ), merge or erase fields in a record.
  • Apply a default operation on a field or on the whole input record.

PatchOperationClause

rule PatchOperationClause ::=
'insert' PatchField '=>' ComplexExprImut
| 'upsert' PatchField '=>' ComplexExprImut
| 'update' PatchField '=>' ComplexExprImut
| 'erase' PatchField
| 'move' PatchField '=>' PatchField
| 'copy' PatchField '=>' PatchField
| 'merge' PatchField '=>' ComplexExprImut
| 'merge' '=>' ComplexExprImut
| 'default' PatchField '=>' ComplexExprImut
| 'default' '=>' ComplexExprImut
;

How do I insert a new value into a record?

patch {"a": 1, "b": 2, "c": 3 } of
insert "d" => "delta"
end;

It is a semantic error to insert a value if the field already exists:

Error in foo.tremor:2:3
1 | patch {"a": 1, "b": 2, "c": 3 } of
2 | insert "b" => "bravo"
| ^^^^^^^^^^^^^^^^^^^^^ The key that is supposed to be written to already exists: b
3 | end;

How do I update an existing value in a record?

patch {"a": 1, "b": 2, "c": 3 } of
update "b" => "bravo"
end;

It is a semantic error to update a value if the field does not already exist:

    1 | patch {"a": 1, "b": 2, "c": 3 } of
2 | update "d" => "delta"
| ^^^^^^^^^^^^^^^^^^^^^ The key that is supposed to be updated does not exists: d
3 | end;

How do I insert or update a value in a record?

If the distinction between an insert and an update is not significant the upsert operation will insert a new field, or update an existing field. This operation is more flexible, but does not offer compile time errors to protect against invalid usage. Where possible, use insert or update in preference to upsert when a new field or replacing an existing fields value would be an error given the business logic at hand.

How do I erase a field from a record?

patch {"a": 1, "b": 2, "c": 3 } of
erase "d"
end;

The field c is removed from our record

How do I rename a field?

patch {"a": 1, "b": 2, "c": 3 } of
move "c" => "d" # The value MUST be a string literal as it represents a field name
end;

The c field is removed and a d field is added with the value from c

How do I duplicate a field?

Similar to move, the copy operation copies the value of one field to a new field

patch {"a": 1, "b": 2, "c": 3 } of
copy "c" => "d" # The value MUST be a string literal as it represents a field name
end;

The c field is preserved, and the d field is added with a copy of the value from c

Can I use patch and merge together?

The merge operation in a patch expression can be applied to the patch target record or to a specified field.

patch {"a": 1, "b": 2, "c": 3 } of
merge "d" => {}
end;

The field d is created in this case with the empty record.

patch {"a": 1, "b": 2, "c": 3 } of
merge => { "snot": "badger", "b": "bravo" } # This is a terse form of insert for `snot`, and `update for `b`
end;

Defaults

For repetitive or template operations, the default operation allows a patch record to be defined that is effectively merged with the target document

patch event of
default => {"snot": {"badger": "goose"}}
end

If event is an empty record, the result is the same as the default value expression. If event has a snot field, the value for snot is preserved. The default value is not used.

Like merge operations, the default merge operation can be very effective for reducing the boilerplate complexity of patch operations and improving the readability of the transformations being performed by readers of the code.

For example, we could limit our default record patch to apply to only the snot field as follows:

patch event of
default "snot" => {"badger": "goose"}
end

Rule PatchField

The PatchField is a string literal identifying a the field of a record to which a PatchOperationClause is being applied.

PatchField

rule PatchField ::=
StringLiteral
;

Rule ForCaseClauses

The ForCaseClausest defines a sequence of case clauses in an mutable for comprehension.

ForCaseClauses

rule ForCaseClauses ::=
ForCaseClause
| ForCaseClauses ForCaseClause
;

A set of one or many case clauses for record key-value or array index-element comprehensions

Rule ForCaseClause

The ForCaseClause defines the case clause for mutable for comprehensions.

ForCaseClause

rule ForCaseClause ::=
'case' '(' Ident ',' Ident ')' WhenClause Effectors
;

Record Comprehension

for { "snot": "badger" } of
case (name, value) => value
end;

Array Comprehension

for [1, "foo", 2, "bar"] of
case (index, value) => value
end;

Guards

use std::type;

for [1, "foo", 2, "bar"] of
case (index, value) when type::is_string(value) => { "string": value }
case (index, value) when type::is_integer(value) => { "integer": value }
end;

Rule ForCaseClausesImut

The ForCaseClausesImut defines a sequence of case clauses in an immutable for comprehension.

ForCaseClausesImut

rule ForCaseClausesImut ::=
ForCaseClauseImut
| ForCaseClausesImut ForCaseClauseImut
;

A set of one or many case clauses for record key-value or array index-element comprehensions

Rule ForCaseClauseImut

The ForCaseClauseImut defines the case clause for immutable for comprehensions.

ForCaseClauseImut

rule ForCaseClauseImut ::=
'case' '(' Ident ',' Ident ')' WhenClause EffectorsImut
;

Record Comprehension

for { "snot": "badger" } of
case (name, value) => value
end;

Array Comprehension

for [1, "foo", 2, "bar"] of
case (index, value) => value
end;

Guards

use std::type;

for [1, "foo", 2, "bar"] of
case (index, value) when type::is_string(value) => { "string": value }
case (index, value) when type::is_integer(value) => { "integer": value }
end;

Rule EffectorsImut

The EffectorsImut rule defines the result value block sequence of pattern rule.

The effectors block provides the result value of case and default clauses in match statements, for comprehensions.

EffectorsImut

rule EffectorsImut ::=
'=>' BlockImut
;

Example

An effector is an => arrow followed by Block sequence.

In many of the structural forms such as match, for or patch and effector is a sequence of logic that is executed when certain conditions occur. The final statement in an effector is the result of the sequence of executions.

As an example, here is a for compresension that enumerates a list and computes the stringified representation of the elements of the list.

The for expression collects each iterations result from the effector's block statement and aggregates them into a list.

for [1, 2, 3, 4, 5] of
case (i, e) => "#{e}";
end;

Rule Predicates

The Predicates rule defines a sequence of mutable PredicateClause rules in tremor.

Predicates

rule Predicates ::=
PredicateClause
| Predicates PredicateClause
;

An illustration of the rule is a set of case statements, followed by an optional default case

  match event of
case %{} => "I am a possibly non-empty record",
case %[] => "I am a possibly non-empty array",
case %( "snot" ) => "I am a list with 1 element which is the string \"snot\"
default => "I'm something else"
end

Rule PredicateClause

The PredicateClause rule defines the forms of a mutable match statement in tremor.

PredicateClause

rule PredicateClause ::=
'case' CasePattern WhenClause Effectors
| 'default' Effectors
;

How do i write robust match predicate rules?

There are two basic forms of match expression predicate

Case form

  match event of
case %{} => "I am a possibly non-empty record",
case %[] => "I am a possibly non-empty array",
case %( "snot" ) => "I am a list with 1 element which is the string \"snot\"

These are used for isolating specific cases of interest that need to specific processing. Sometimes cases can be incomplete without a default case and this is also supported.

    default => "If i'm not one of these things, I'm something else"
end

If tremor can prove at compile time that a default case is advisable it will emit a warning:

match event of
case true => "I believe you"
end;
    1 | match event of
2 | case true => "I believe you"
3 | end;
| ^^^ This match expression has no default clause, if the other clauses do not cover all possibilities this will lead to events being discarded with runtime errors.

And, tremor will issue a runtime error when a bad case is found:

    1 | match event of
2 | case true => "I believe you"
3 | end;
| ^^^ A match expression executed but no clause matched
| NOTE: Consider adding a `default => null` clause at the end of your match or validate full coverage beforehand.

It is almost always preferable to have a default case and this practice is recommended.

Rule CasePattern

The CasePattern rule defines the valid structural pattern matching forms available in a match statement's case clause.

CasePattern

rule CasePattern ::=
RecordPattern
| ArrayPattern
| TuplePattern
| ComplexExprImut
| '_'
| '~' TestExpr
| Ident '=' CasePattern
;

An internal part of the match statement rule supporting

  • Record, Array and Tuple structural patterns
  • Complex predicate expressions
  • The "_" dont care condition
  • A predicate extractor
  • An aliased case pattern

Rule Block

The Block rule defines a semi-colon delimited set of Expr rules.

Block

rule Block ::=
Expr
| Block ';' Expr
;

How does tremor process blocks?

A block of expressions is a ; semi-colon delimited set of statements that share the same scope. This means that the same set of metadata, state and any scoped identifiers are visible to the block.

The last expression in a block of statements is the return value.

let return = 1;
let return = return << 7 % 4;
return - 1

The answer as we're sure you'll agree is 7.

Rule PredicatesImut

The PredicatesImut rule defines a sequence of PredicateClauseImut rules.

PredicatesImut

rule PredicatesImut ::=
PredicateClauseImut
| PredicatesImut PredicateClauseImut
;

An illustration of the rule is a set of case statements, followed by an optional default case

  match event of
case %{} => "I am a possibly non-empty record",
case %[] => "I am a possibly non-empty array",
case %( "snot" ) => "I am a list with 1 element which is the string \"snot\"
default => "I'm something else"
end

Rule PredicateClauseImut

The PredicateClauseImut rule defines valid clauses of a match statement.

Two forms are supported:

  • A case expression with optional guard expression and mandatory effector block.
  • A default case expression with effector block.

PredicateClauseImut

rule PredicateClauseImut ::=
'case' CasePattern WhenClause EffectorsImut
| 'default' EffectorsImut
;

How do i write robust match predicate rules?

There are two basic forms of match expression predicate

Case form

  match event of
case %{} => "I am a possibly non-empty record",
case %[] => "I am a possibly non-empty array",
case %( "snot" ) => "I am a list with 1 element which is the string \"snot\"

These are used for isolating specific cases of interest that need to specific processing. Sometimes cases can be incomplete without a default case and this is also supported.

    default => "If i'm not one of these things, I'm something else"
end

If tremor can prove at compile time that a default case is advisable it will emit a warning:

match event of
case true => "I believe you"
end;
    1 | match event of
2 | case true => "I believe you"
3 | end;
| ^^^ This match expression has no default clause, if the other clauses do not cover all possibilities this will lead to events being discarded with runtime errors.

And, tremor will issue a runtime error when a bad case is found:

    1 | match event of
2 | case true => "I believe you"
3 | end;
| ^^^ A match expression executed but no clause matched
| NOTE: Consider adding a `default => null` clause at the end of your match or validate full coverage beforehand.

It is almost always preferable to have a default case and this practice is recommended.

Rule RecordPattern

The RecordPattern defines structural patterns against record values.

Record patterns start with the %{ operator and end with '}'.

Patterns may be empty %{}, or a sequence of record pattern fields.

Record patterns are search oriented based on predicate matching.

Ordinal, order or position based matching in records is not defined.

RecordPattern

rule RecordPattern ::=
'%{' PatternFields '}'
| '%{' '}'
;

An empty record pattern

Matches any record value

%{ }

A record with a field called 'snot'

%{ snot }

A record with a field called 'snot', with a string literal value 'badger'

%{ snot == "badger" }

A record with a field called 'snot', whose string contents is well-formed embedded JSON

%{ snot ~= json|| }

Rule ArrayPattern

The ArrayPattern defines structural patterns against array values.

Array patterns start with the %[ operator and end with ].

Patterns may be empty %[], or a sequence of array predicate patterns.

Array patterns are search oriented based on predicate matching.

Where ordinal matching is needed then a TuplePattern may be preferential.

ArrayPattern

rule ArrayPattern ::=
'%[' ArrayPredicatePatterns ']'
| '%[' ']'
;

match event of
case result = %[ 1, 2 ] => result
case %[ _ ] => "ignore"
default => null
end

Rule TuplePattern

The TuplePattern defines structural patterns against tuple values.

Tuple patterns start with the %( operator and end with ).

Patterns may be empty %(), %(...) any, or a sequence of tuple patterns followed by an optional open tuple ... match.

Tuple patterns are ordinal patterns defined against arrays.

Where search like predicate filters are preferential the ArrayPattern may be a better choice.

TuplePattern

rule TuplePattern ::=
'%(' TuplePredicatePatterns OpenTuple ')'
| '%(' ')'
| '%(' '.' '.' '.' ')'
;

A tuple pattern allows ordinal matching of arrays. A tuple pattern is useful where the search oriented %[ .. ] array pattern syntax is insufficient or when the order of entries or elements in an array is significant.

use std::string;

match string::split(event, "/") of
case %("snot") => 0 # An array with a single string literal 'snot' value
case %("snot", ...) => 1 # An array with a first value string literal 'snot', and possibly zero or many more values
case %("api", _, "badger", ...) => 2 # An array with first value 'api', and 3rd value 'badger'
case %("") => 3 # An array with an empty string literal value
case %("badger", "snot") => 4 The two element array with 1st element "badger", and 2nd element "snot"
default => string::split(event, "/")
end

Rule TestExpr

The TestExpr defines an extractor with an optional microformat body.

A test expression has a predicate component. The Ident defines the expected microformat the value being tested in a structural pattern match should conform to.

If this validates, then an optional microformat expression that is specific to the extractor named by the Ident is employed to extract content from the value into a value that tremor can process.

TestExpr

rule TestExpr ::=
Ident TestLiteral
;

json||

The rule identifies an extractor by name and delimits any micro-format arguments using the '|' pipe symbol.

In the above example the extractor is a JSON recognizer that can detect well formed JSON embedded inside a string literal. Such values will match the test expression and be parsed so that the content can be used in logic expressions.

Rule BlockImut

The BlockImut rule defines a comma delimited sequence of complex immutable expressions.

BlockImut

rule BlockImut ::=
ComplexExprImut
| BlockImut ',' ComplexExprImut
;

How does tremor process blocks?

A block of expressions is a ; semi-colon delimited set of statements that share the same scope. This means that the same set of metadata, state and any scoped identifiers are visible to the block.

The last expression in a block of statements is the return value.

let return = 1;
let return = return << 7 % 4;
return - 1

The answer as we're sure you'll agree is 7.

Rule PredicateFieldPattern

The PredicateFieldPattern rule defines the legal predicate tests available within record patterns.

Record patterns can use:

  • Extractor test expressions against fields.
  • Record, array and tuple patterns against fields.
  • Equality and comparison predicate patterns against fields.
  • Presence patterns against fields.

PredicateFieldPattern

rule PredicateFieldPattern ::=
Ident '~=' TestExpr
| Ident '=' Ident '~=' TestExpr
| Ident '~=' RecordPattern
| Ident '~=' ArrayPattern
| Ident '~=' TuplePattern
| 'present' Ident
| 'absent' Ident
| Ident BinCmpEq ComplexExprImut
;

Extraction

x ~= json||

Tests if the field x represents an embedded json script. If true, extracts and parses the embedded JSON and stores the parsed document in the field x in the predicate patterns result, if configured.

Aliased extraction

alias = x ~= json||

Tests if the field x represents an embedded json script. If true, extracts and parses the embedded JSON and stores the parsed document in the field alias in the predicate patterns result, if configured.

Sub records

x ~= %{}

Tests if the field x represents a record value. If true, extracts embedded record and stores it in the field x in the predicate patterns result, if configured.

Sub arrays

x ~= %[]

Tests if the field x represents an array value. If true, extracts embedded array and stores it in the field x in the predicate patterns result, if configured.

x ~= %()

Tests if the field x represents an array value. If true, extracts embedded array and stores it in the field x in the predicate patterns result, if configured.

Presence and absence

present x

Is the field x present in the record? If true, extracts the field.

absent x

Is the field x absent in the record?

Comprison and Equality tests

x >= 10

Tests if the numeric field x is greater than or equal to the literal 10. If true, extracts the field.

Rule BinCmpEq

The BinCmpEq rule allows binary or comparative operations

Comparitive and Equality operations have the same precedence.

BinCmpEq

rule BinCmpEq ::=
BinEq
| BinCmp
;

Rule TestLiteral

The TestLiteral rule specifies an extractor microformat block.

An extractor takes the general form:

Ident '|' MicroFormat '|'

Where

The ident is the name of a builtin extractor such as json or base64.

The Microformat content depends on the extractor being used

TestLiteral

rule TestLiteral ::=
'<extractor>'
;

Extracting JSON embedded within strings

let example = { "snot": "{\"snot\": \"badger\"" };
match example of
case extraction=%{ snot ~= json|| } => extraction.snot
default => "no match"
end;

When executed this will result in:

"badger"

Decoding base64 embedded within strings

let example = { "snot": "eyJzbm90IjogImJhZGdlciJ9Cg==" };
match example of
case extraction=%{ snot ~= base64|| } => extraction.snot
default => "no match"
end;

When executed this will result in:

"{\"snot\": \"badger\"}

Wrap and Extract

We can decode the base64 decoded string through composition:

let example = { "snot": "eyJzbm90IjogImJhZGdlciJ9Cg==" };
match example of
case decoded = %{ snot ~= base64|| } =>
match { "snot": decoded.snot } of
case json = %{ snot ~= json|| } => json.snot.snot
default => "no match - json"
end
default => "no match - base64"
end;

Rule PatternFields

The PatternFields rule defines a set of comma delimited PredicateFieldPattern rules.

PatternFields

rule PatternFields ::=
PatternFields_
;

Wraps a macro invocation rule for for use in other rules.

Rule TuplePredicatePatterns

The TuplePredicatePatterns rule defines a set of comma delimited TuplePredicatePattern rules.

TuplePredicatePatterns

rule TuplePredicatePatterns ::=
TuplePredicatePatterns ',' TuplePredicatePattern
| TuplePredicatePattern
;

See ArrayPredicatePattern rule for predicate patterns avilable in tuple predicate patterns.

The predicate patterns are essentially the same, with the distinction that tuple patterns are ordinal and array predicate patterns are search based.

Rule OpenTuple

The OpenTuple rule defines a tuple pattern that matches any element in a tuple from the position it is used and subseuent elements.

It can only be used as an optional final predicate in a TuplePattern.

OpenTuple

rule OpenTuple ::=
( ',' '.' '.' '.' ) ?
;

%("snot", ...)

An open tuple that starts with ["snot"] but may have zero or more extra elements

Rule TuplePredicatePattern

The syntax of the TuplePredicatePattern is the same as that of the ArrayPredicatePattern.

TuplePredicatePattern

rule TuplePredicatePattern ::=
ArrayPredicatePattern
;

Wraps an ArrayPredicatePattern as the predicates supported by Array and Tuple predicate patterns are the same.

See the ArrayPredicatePattern rule for more details

Rule ArrayPredicatePattern

The ArrayPredicatePattern rule defines predicate patterns for structural pattern matching against array values.

ArrayPredicatePattern

rule ArrayPredicatePattern ::=
'~' TestExpr
| '_'
| ComplexExprImut
| RecordPattern
;

Array predicate extraction - contains embedded JSON

~ json||

Contains records

%{}

Rule PatternFields_

The PatternFields_ rule is a rule that defines a comma separated set of PatternField definitions.

The rule follows the semantics defined in the Sep macro.

PatternFields_

rule PatternFields_ ::=
Sep!(PatternFields_, PredicateFieldPattern, ",")
;

See PatternFields rule for details.

This rule wraps away a lalrpop macro call for ease of reference in other rules in the grammar source.

Rule Fields_

The Fields_ rule is a rule that defines a comma separated set of field definitions.

The rule follows the semantics defined in the Sep macro.

Fields_

rule Fields_ ::=
Sep!(Fields_, Field, ",")
;

See Fields rule for details.

This rule wraps away a lalrpop macro call for ease of reference in other rules in the grammar source.

Rule Bytes

The Bytes rule defines a sequence of bit syntax patterns in a binary tremor literal representation.

A legal sequence of bytes MUST contain at least one byte part segment.

Byte part segments are comma ( ',' ) delimited.

Bytes

rule Bytes ::=
BytesPart
| Bytes ',' BytesPart
;

Example: How do I encode a TCP packet?

# Convert the record into a binary encoded TCP packet
binary::into_bytes(<<
# Encode source and destination TCP ports, each 16 bits wide
event.src.port:16, event.dst.port:16,
# Encode sequence, 32 bits wide
event.seq:32,
# Encode acknowldgement, 32 bits wide
event.ack:32,
# Encode TCP conditioning and flags fields
event.offset:4, event.res:4, event.flags:8, event.win:16,
# Encode checksum; and urgent bytes from first byte
event.checksum:16, event.urgent:16,
# Encode data using the encoded length of another binary literal
event.data/binary
>>)

Rule BytesPart

The BytesPart rule represents sub segment of a binary encoded literal

If the part is the last segment in a bytes literal, it can be of arbitrary length.

If the part is not the last segment, it must specify its length in bits.

BytesPart

rule BytesPart ::=
SimpleExprImut
| SimpleExprImut ':' 'int'
| SimpleExprImut '/' Ident
| SimpleExprImut ':' 'int' '/' Ident
;

Form

The part may take the following general form

SimpleExprImut  ':'  'int'  '/' Ident 

Where:

  • The `SimpleExprImut can be a literal or identifier to the data being encoded.
  • A optional size in bits, or defaulted based on the data being encoded.
  • An optional encoding hint as an identifier

Size constraints

The size must be zero or greater, up to and including but no larger than 64 bits.

Encoding Hints

IdentDescription
binaryEncoded in binary, using network ( big ) endian
big-unsigned-integerUnsigned integer encoding, big endian
little-unsigned-integerUnsigned integer encoding, little endian
big-signed-integerSigned integer encoding, big endian
little-signed-integerSigned integer encoding, little endian

Rule Sep

The Sep rule is a LALRPOP convenience that allows defining a macro rule template for a common sub rule sequence.

The Sep macro rule definition in tremor DSLs allows lists or sequences of expressions to be separated by a specified delimiter. The delimiter is optional for the final item in a list or sequence.

ArgumentDescription
TThe term rule - specifies what is to be separated
DThe delimiter rule - specifies how elements are separated
LA list of accumulated terms

Sep

macro Sep<L, T, D> ::=
T D L
| T D ?
;

Rule BinOp

The BinOp rule is a LALRPOP convenience that allows defining a macro rule template for a common sub rule sequence.

The BinOp macro rule definition in tremor DSLs allows binary operations to be defined tersely

ArgumentDescription
CurrentThe current rule permissible for the LHS of the expression
OperationThe operation to be performeed
NextThe current rule permissible for the RHS of the expression

The macro imposes rule precedence where the left hand side expression takes higher precedence relative to the right hand side expression when interpreted by tremor.

Considerations

Tremor performs compile time optimizations such as constant folding. So literal expressions of the form 1 + 2 may compile to a constant ( 3 in this case ) and have no runtime cost.

BinOp

macro BinOp<Op, Current, Next> ::=
( Current ) ( Op ) Next
;