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Wrong grammar for match. #774

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steffahn opened this issue Mar 4, 2020 · 1 comment · Fixed by #776
Closed

Wrong grammar for match. #774

steffahn opened this issue Mar 4, 2020 · 1 comment · Fixed by #776
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A-grammar Area: Syntax and parsing

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@steffahn
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steffahn commented Mar 4, 2020

In the grammar for match, i.e. for the nonterminal MatchExpression, in MatchArms the right-hand side of the non-last arms only allows skipping the , for BlockExpression. However it seems to be the case that any ExpressionWithBlock works without the ,. Is this correct?

Furthermore, currently the case of a BlockExpression followed by , matches both alternatives of the BlockExpression ,? | Expression ,. Perhaps a nicer rule would use ExpressionWithoutBlock , | ExpressionWithBlock ,?, in effect being similar to my proposed rule for ExpressionStatement in #773, but with comma instead of semicolon.

Finally, in the last arm, the BlockExpression | Expression part seems a bit redundant as a BlockExpression is an Expression.
@ehuss
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ehuss commented Mar 4, 2020

This all sounds like good changes to me.

@ehuss ehuss added the A-grammar Area: Syntax and parsing label Mar 4, 2020
@steffahn steffahn mentioned this issue Mar 4, 2020
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Havvy pushed a commit to Havvy/reference that referenced this issue Aug 25, 2020
@steffahn @Havvy
Fix expression and statement grammar.
027f10a 
Semicolon or comma in expression statements or match arms, respectively, are optional, but part of the statement / match arm.
Also remove a note about proc-macros from the page about BlockExpression.
Closes rust-lang#773 and closes rust-lang#774.
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Fix expression and statement grammar.
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@ehuss @steffahn