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> Currently, the expression `f.g` will attempt to compose the function bound to `f` with the function bound to `g`. So what will this mean now? Will function c

• duijf 6y ago
  From https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0282-record-dot-syntax.rst#lexer https://github.com/ghc-proposals/ghc-proposals/blob/master/p... .g is a field selector. f.g is field selection of a record. f . g is function composition. f. g is function composition.
  • moomin 6y ago
    Whilst I'm not going to argue the proposal is a bad thing, I think you've just summarized why some are giving it the side eye pretty well.
    • ben509 6y ago
      To me it's just, "the dot hugs a field, dot by itself is composition, and module names are capitalized." While I wouldn't write f. g, if I see it, it's not hugging the field name so it's composition. I don't think I'd have trouble reading it. But... it will probably trip up newbies and people with odd spacing styles. Hopefully GHC can give a useful error like "In the field selection expression f.g, g is a function defined on XX. Did you mean f . g?"
  • thomasahle 6y ago
    (.g) us a field selector, is (. g) then a function :: (a -> b) -> c -> b?
    • giraj 6y ago
      Yep! You could check this in GHCi (the repl), for example: > :t (. id) > (. id) :: (b -> c) -> b -> c (:t prints the type of an expression, and id is the "identity function" that's b -> b here.) (EDIT: Maybe you know the above and you're asking if it's being changed in the proposal. It doesn't seem so to me.)
      • thomasahle 6y ago
        I'm just pointing out that the difference between (.g) and (. g) is potentially easy to miss.