Hi everyone,

Joachim and Richard, thank you very much for creating this framework to think about this proposal. It is very helpful.

As an educator, I'd vote for rejection. My reason is that the proposal introduces yet another style of programming in Haskell, in addition to traditional functional and lenses-like ones. I can easily imagine imitating object-oriented style with fields-functions and it will be too tempting to use it by those with OO-background (and this includes almost everyone these days given the trends in higher education). The proposal also limits ways to use function composition (especially in sections) which is another sad thing. I don't like all this happening to Haskell as a purely functional PL.

Regards,

Vitaly

сб, 14 дек. 2019 г. в 14:42, Richard Eisenberg <rae@richarde.dev>:

Your very helpful delineation of the space assumes (.) = \ f g x -> f (g x) and then inlines. I actually think it would be clearer not to do this. I have taken your taxonomy and kept (.) abstract. Some examples also left (x.field) uninterpreted. I have expanded these to use getField. To be clear, this is *not* a reproposal or intended to make *any* change to Joachim's dichotomy. I am just restating it a way I understand better. Perhaps others will also find this to be clearer. Each individual committee member can use *either* my presentation or Joachim's. They (are intended to) have *the same* semantics.

Reject:
r.field        = (.) r field
f x.field y    = (.) (f x) (field y)
f x .field y   = (.) (f x) (field y)
f x (.field) y = f x (\a -> (.) a field) y
f x (.field y) = f x (\a -> (.) a (field y))

OnlySelection:
r.field        = getField @"field" r
f x.field y    = f (getField @"field" x) y
f x .field y   -- NOT ALLOWED
f x (.field) y -- NOPE
f x (.field y) -- NAY

SectionSelector:
r.field        = getField @"field" r
f x.field y    = f (getField @"field" x) y
f x .field y   -- VERBOTEN!
f x (.field) y = f x (\r -> getField @"field" r) y
f x (.field y) -- BAD!

PlainSelector:        -- this is the proposal as it stands, I believe
r.field        = getField @"field" r
f x.field y    = f (getField @"field" x) y
f x .field y   = f x (\r -> getField @"field" r) y
f x (.field) y = f x (\r -> getField @"field" r) y
f x (.field y) = f x ((\r -> getField @"field" r) y) = f x (getField @"field" y) -- !

Ocaml:
r.field        = getField @"field" r
f x.field y    = f (getField @"field" x) y
f x .field y   = f (getField @"field" x) y
f x (.field) y -- NOT ALLOWED
f x (.field y) -- CAN’T DO THAT

Ocaml+Section:
r.field        = getField @"field" r
f x.field y    = f (getField @"field" x) y
f x .field y   = f (getField @"field" x) y
f x (.field) y = f (\r -> getField @"field" r) y
f x (.field y) -- NO NO NO

JS:
r.field        = getField @"field" r
f x.field y    = (getField @"field" (f x)) y
f x .field y   = (getField @"field" (f x)) y
f x (.field) y -- IMPOSSIBLE!
f x (.field y) -- STOP IT PLEASE!

JS+Section:
r.field        = getField @"field" r
f x.field y    = (getField @"field" (f x)) y
f x .field y   = (getField @"field" (f x)) y
f x (.field) y = f x (\r -> getField @"field" r) y
f x (.field y) = f x (\r -> (getField @"field" r) y)

I hope this is helpful!
Richard
_______________________________________________
ghc-steering-committee mailing list
ghc-steering-committee@haskell.org
https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee