✨ feat(lang): add -> (Arrow) syntax as shorthand for fn

[harehare]

Add Arrow (->) as an alternative syntax for anonymous functions, equivalent to fn. Includes lexer token, CST/AST parser support, formatter support, and tests for all layers.

Also fix CST parse_arg() to accept Arrow tokens so -> can be used as a function call argument (e.g. map(->(): ...)).

[codspeed-hq]

Merging this PR will not alter performance

✅ 29 untouched benchmarks

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_{Comparing feat/arrow-syntax (1649d5f) with main (f531b14)}

[Copilot]

Pull request overview

Adds -> (Arrow) as an alternative surface syntax for anonymous functions in mq-lang, integrating it through lexing, CST/AST parsing, and formatting, with accompanying tests to ensure consistent behavior across layers.

Changes:

• Introduce TokenKind::Arrow and lex -> as its own token.
• Extend CST and AST parsers to treat Arrow equivalently to fn, including allowing it as a call argument.
• Add formatter test coverage for arrow-function formatting scenarios.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
crates/mq-lang/src/lexer/token.rs	Adds TokenKind::Arrow and display formatting/tests for ->.
crates/mq-lang/src/lexer.rs	Adds lexer support and tokenization tests for the -> token.
crates/mq-lang/src/cst/parser.rs	Allows -> wherever fn is accepted (including call args) and adds CST tests.
crates/mq-lang/src/ast/parser.rs	Accepts -> as a fn equivalent in the AST parser and adds AST tests.
crates/mq-formatter/src/formatter.rs	Adds formatter tests validating arrow-function output and spacing/newline behavior.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.