Re: [GHC] #1215: GHC fails to respect the maximal munch rule while lexing "qualified reservedids"
Context if you haven't been following: http://hackage.haskell.org/trac/ghc/ticket/1215 On Tue, Mar 13, 2007 at 03:12:33PM -0000, GHC wrote:
Interesting. It turns out I misinterpreted the Haskell lexical syntax: GHC lexes `M.default` as `M` `.` `default`, because `M.default` is not a valid qvarid but I neglected to take into account the maximal munch rule.
We have an open ticket for Haskell' about this: http://hackage.haskell.org/cgi-bin/haskell-prime/trac.cgi/wiki/QualifiedIden... which was until just now inaccurate (I've now fixed it). I propose to fix GHC in 6.8 to match the Haskell' proposal.
If I understand correctly then the proposal would make e.g. foo = Bar.where a syntactically valid program, but one which would be guaranteed to fail to compile with a not-in-scope error? Wouldn't it be cleaner for it to be a lexical error? Unfortunately I'm not sure how to say this in the grammar; the best I can come up with is: program -> {lexeme | whitespace | error } error -> [ modid . ] reservedid Thanks Ian
Ian Lynagh wrote:
Context if you haven't been following: http://hackage.haskell.org/trac/ghc/ticket/1215
On Tue, Mar 13, 2007 at 03:12:33PM -0000, GHC wrote:
Interesting. It turns out I misinterpreted the Haskell lexical syntax: GHC lexes `M.default` as `M` `.` `default`, because `M.default` is not a valid qvarid but I neglected to take into account the maximal munch rule.
We have an open ticket for Haskell' about this: http://hackage.haskell.org/cgi-bin/haskell-prime/trac.cgi/wiki/QualifiedIden... which was until just now inaccurate (I've now fixed it). I propose to fix GHC in 6.8 to match the Haskell' proposal.
If I understand correctly then the proposal would make e.g.
foo = Bar.where
a syntactically valid program, but one which would be guaranteed to fail to compile with a not-in-scope error?
Wouldn't it be cleaner for it to be a lexical error? Unfortunately I'm not sure how to say this in the grammar; the best I can come up with is:
program -> {lexeme | whitespace | error } error -> [ modid . ] reservedid
Or make lexeme overlap with error, and do this: program -> { lexeme_<error> | whitespace } to make it clear that a valid program doesn't contain any error lexemes. But then people might wonder why the error production doesn't contain all the lexical errors. I don't really have a strong opinion here, but I lean towards not doing this, on the grounds that it's not strictly necessary and I'm a bit of a minimalist. The compiler is already free to report the error as a lexical error if it likes. Cheers, Simon
participants (2)
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Ian Lynagh -
Simon Marlow