lezer-elixir

Elixir grammar for the Lezer parser system.

Design

This grammar is based directly on tree-sitter-elixir and closely mirrors its syntax tree and decisions. All the test cases are adapted from there as well. Refer to the corresponding repository for further documentation.

Differences

The Elixir syntax tree is very generic. Most of the language built-ins, such as a function definition, are no different than user-defined functions. It is only for the purpose of highlighting, where it makes sense to distinguish certain keywords.

tree-sitter allows pattern matching on arbitrary fragments of the syntax tree, which is flexible enough to correctly tag nodes for highlighting in all cases. On the other hand, in Lezer the highlighting queries are more strict, for performance reasons. Under these restrictions, we need a more specialized syntax tree that, for example, uses separate nodes for function definition call and regular function call. Additionally, Lezer does not support annotating nodes with "fields", for example, to distinguish between operator left and right expression. In cases where we need those, an explicit nodes are required.

Given that, this grammar describes a syntax tree that is a superset of the tree-sitter one. The following additional nodes are present:

• Identifier specializations

  • SpecialIdentifier (__MODULE__)
  • UnderscoredIdentifier (_x)

• Call specializations

  • FunctionDefinitionCall (def fun(x), do: 1)
  • KernelCall (if) - in addition to Call

• UnaryOperator specializations

  • AtOperator (@x)
  • DocOperator (@doc "...")
  • CaptureOperator (&fun/1)
  • CaptureOperand (&1)

• BinaryOperator specializations

  • WhenOperator (left when right)
  • PipeOperator (left |> right)

• Sigil specializations

  • StringSigil (~s"string", ~S"string")

• named operator groups

  • Operator (+)
  • WordOperator (and)

• explicitly included tokens

  • do, end, fn, after, else, catch, rescue
  • all brackets

• fields:

  • Right node in WhenOperator, PipeOperator and Dot to distinguish the left and right operand (note that this is enough to make the distinction, we don't need Left, which would result in more conflicts when introduced)
  • we do not need an explicit "target" node for calls, because arguments are already separated under the Arguments node, hence anything else on that level is the target

License

Copyright (C) 2024 Dashbit

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at [http://www.apache.org/licenses/LICENSE-2.0](http://www.apache.org/licenses/LICENSE-2.0)

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.