Re: [GHC] #14812: Dot-Notation for Flipped Function Application

16 Feb 2018

      #14812: Dot-Notation for Flipped Function Application
-------------------------------------+-------------------------------------
        Reporter:  tepan             |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by tepan:

Old description:
...
Please allow to put a dot `.` (without spaces) between two things for
''flipped'' function application. This could make for code in pseudo-OOP
style:
{{{#!hs
encrypt(str) = do {
  str.map(succ);
}
}}}
Currently, as a workaround, this can be achieved by defining `(.) = flip
($)` (making `.` for function composition unavailable, though):
{{{#!hs
encrypt(str) = do {
  str.map(succ);
} where (.) = flip ($)
}}}
(For a remotely similar look-and-feel, one could use
`Data.Function.((&))` instead of `(.)`.)
Please note that `.` without spaces is already an OOP-like notational
convenience in order to denote Modules and their elements.
{{{#!hs
x = do {
  Prelude.length("Hello World!");
}
}}}
This means, that a distinction between ` . ` (with spaces) and `.`
(without spaces) is already been made, which is why `Just . Just $ 42`
compiles, wheras `Just.Just $ 42` doesn't. Analogously, with this Feature
Request implemented, `"Hello".map(succ)` would compile whereas `"Hello" .
map(succ)"` wouldn't.
New description:

 Please allow to put a dot `.` (without whitespaces) between two things for
 ''flipped'' function application. This could make for code in pseudo-OOP
 style:

 {{{#!hs
 encrypt(str) = do {
   str.map(succ);
 }
 }}}

 Currently, as a workaround, this can be achieved by defining `(.) = flip
 ($)` (making `.` for function composition unavailable, though):

 {{{#!hs
 encrypt(str) = do {
   str.map(succ);
 } where (.) = flip ($)
 }}}

 (For a remotely similar look-and-feel, one could use `Data.Function.((&))`
 instead of `(.)`.)

 Side note: `.` without whitespaces is already an OOP-like notational
 convenience in order to denote Modules and their elements in Haskell.

 OOP:
 * `Prelude.length("Hello")` (static function `length` of class `Prelude`
 applied to `"Hello"`)

 Haskell:
 * `Prelude.length("Hello")` (function `length` of module `Prelude` applied
 to `"Hello"`)

 This means, that a distinction between ` . ` (with whitespaces) and `.`
 (without whitespaces) is already been made, which is why `Just . Just $
 42` compiles, whereas `Just.Just $ 42` doesn't. Analogously, with this
 Feature Request implemented, `"Hello".map(succ)` would compile whereas
 `"Hello" . map(succ)"` wouldn't.

 Current dot-notation for modules (not to be changed):
 * `Foo.bar` (`bar` of module `Foo`)

 Proposed dot-noation for function application:
 * `foo.bar` (function `bar` applied to `foo`)

--

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14812#comment:7
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