Re: [Haskell-cafe] Parsing Haskell with Layout

Great, thanks! On 08/29/2018 12:32 PM, J. Garrett Morris wrote:

On Tue, Aug 28, 2018 at 2:53 PM Benjamin Redelings wrote:

...

I'm not sure of the theory behind implementing Note 5 in section 10.3. This says roughly that we insert a "}" token after token t[n] if the tokens t[1]...t[n+1] have no valid parses, and the sequence of tokens t[1] ... t[n] followed by "}" DO have a valid parse.

I think this allows you to write

f z = let x=2;y=3 in x+y+z Yes.

...

(a) what concepts are assumed by the report that would make it "obvious" how Note 5 is supposed to be implemented? I don't think the report is intending to suggest a particular implementation approach. GHC's is described at https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/Parser.

...

(b) a simple (hopefully) implementation strategy for implementing it? I'm looking for a language-independent approach for parsing. Perhaps you would find Michael Adams "Principled parsing for indentation-sensitive languages: Revisiting Landin’s offside rule" helpful. http://dx.doi.org/10.1145/2429069.2429129

That approach is implemented by the "indentation" library on Hackage, for either Parsec or Trifecta.

/g