I like the approach from "Principled Parsing for Indentation-Sensitive
Languages" (https://michaeldadams.org/papers/layout_parsing/)
On Wed, Nov 1, 2023 at 8:32 AM Travis Athougies
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According to the Haskell report [1] (See Note 5), a virtual `}` token is inserted if parsing the next token would cause a parse error and the indentation stack is non-empty.
I'm trying to lex and parse Haskell source and this sort of interplay (which requires two-way communication between lexer and parser) makes it very difficult to write a conformant implementation.
I can't change the standard (obviously), but I'm wondering if this is actually what GHC (de facto the only Haskell compiler) does, or if it applies some other rule. If so, does anyone know the exact mechanism of its implementation?
I've been programming Haskell for more than a decade, and while I have an intuitive understanding of the indentation rules, I would have assumed the source could be lexed without also having a parser. In particular, the note seems to imply that the main purpose of this is to properly lex `let`/`in` bindings. Perhaps there's an alternate equivalent rule?
Curious to hear other's thoughts.
Travis
[1]
https://www.haskell.org/onlinereport/haskell2010/haskellch10.html#x17-178000... -----BEGIN PGP SIGNATURE-----
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