Liquid Haskell should accept `UnicodeSyntax`

[0cjs]

Setting {-# LANGUAGE UnicodeSyntax #-} in a source file allows us to use, e.g., → and ∷ as -> and ::, but this doesn't apply to Liquid Haskell code, which even with UnicodeSyntax enabled still accepts only the latter. It would be nice if we could use UnicodeSyntax in Liquid Haskell as well.

(Given that we can't at the moment, I've had to abandon UnicodeSyntax for my projects that use Liquid Haskell, as having a mix of the two in the same file makes searching and the like more difficult.)

[facundominguez]

Thanks @0cjs.

Here's the list of syntax symbols that GHC supports. Of these, perhaps only ->, ::, and => are relevant to LH.

It needs to be seen whether this only affects the LH parser, or LF parser is involved too.

[AlecsFerra]

Can't we reuse the parser from GHC since we are a plugin? Honestly it feels pretty weird having syntax different from Haskell in the refinements

[facundominguez]

The GHC parser would allow for more expressions than LH can handle. We would need to produce errors when the user uses unsupported syntax, produce good location info, and translate the Haskell AST to LH's.

The GHC parser doesn't allow for the syntax of abstract predicates and other decorations, so it could only be used to parse predicates, I suppose.

One inconvenience is that then parsing would be more affected by changes to the GHC AST.

Maybe it can be done. It deserves another issue.

[AlecsFerra]

Uhm ok it sounds like a pain then I don't know if its worth it