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fix typo and formatting issues, tweak wording

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Almost89 2025-02-22 20:21:17 +00:00
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11
docs/syntax-pattern-and-match-expressions.md
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@ -40,7 +40,7 @@ local function parse_simple_expr(): AstExprNode
end end
``` ```
The match expression distils the most important parts of the first example but removes all repetition and verbosity. The match expression distils the most important parts of the first example but removes almost all repetition and verbosity.
## Design ## Design
@ -48,13 +48,12 @@ There are two main components proposed in this RFC:
- patterns, which check if a value *matches* some definition; and - patterns, which check if a value *matches* some definition; and
- match expressions, which match one value to a collection of arms and return a consequence of the arm if it's pattern matches. - match expressions, which match one value to a collection of arms and return a consequence of the arm if it's pattern matches.
The syntax is inspired heavily by [Rust's match expression](https://doc.rust-lang.org/reference/expressions/match-expr.html) and [pattern syntax](https://doc.rust-lang.org/reference/patterns.html) .
The proposed grammar changes are below: The proposed grammar changes are below:
```ebnf ```ebnf
namepattern = NAME | NAME '[' exp ']' | namepattern '.' NAME patternname = NAME | NAME '[' exp ']' | patternname '.' NAME
pattern = NUMBER | STRING | 'nil' | 'true' | 'false' | stringinterp | namepattern | '*' | pattern 'or' pattern | '(' pattern ')' | NUMBER 'until' NUMBER | 'not' pattern pattern = NUMBER | STRING | 'nil' | 'true' | 'false' | stringinterp | patternname | '*' | pattern 'or' pattern | '(' pattern ')' | NUMBER 'until' NUMBER | 'not' pattern
matcharm = pattern ['if' exp] '->' exp matcharm = pattern ['if' exp] '->' exp
matcharmlist = matcharm {',' matcharm} [','] matcharmlist = matcharm {',' matcharm} [',']
matchexp = 'for' exp 'match' '(' matcharmlist ')' matchexp = 'for' exp 'match' '(' matcharmlist ')'
@ -62,6 +61,8 @@ matchexp = 'for' exp 'match' '(' matcharmlist ')'
simpleexp = NUMBER | STRING | 'nil' | 'true' | 'false' | '...' | tableconstructor | attributes 'function' funcbody | prefixexp | ifelseexp | stringinterp | matchexp simpleexp = NUMBER | STRING | 'nil' | 'true' | 'false' | '...' | tableconstructor | attributes 'function' funcbody | prefixexp | ifelseexp | stringinterp | matchexp
``` ```
This syntax is heavily inspired by [Rust's match expression](https://doc.rust-lang.org/reference/expressions/match-expr.html) and [pattern syntax](https://doc.rust-lang.org/reference/patterns.html).
### Patterns ### Patterns
Patterns are the most powerful part of this RFC and without them match expressions would be next to useless. The syntax is designed to be extensible and flexible enough for use in other areas of the language in future. Patterns are the most powerful part of this RFC and without them match expressions would be next to useless. The syntax is designed to be extensible and flexible enough for use in other areas of the language in future.
@ -216,7 +217,7 @@ local sides = for shape match (
"line" -> 1, "line" -> 1,
"triangle" -> 3, "triangle" -> 3,
"square" or "rectangle" -> 4, "square" or "rectangle" -> 4,
"circle" -> error("circle don't have sides"), "circle" -> error("circles don't have sides"),
* -> error(`unknown shape {shape}`), * -> error(`unknown shape {shape}`),
) )
``` ```