#12465: Evil idea: Allow empty record field update syntax for types. -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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: | -------------------------------------+------------------------------------- Description changed by Iceland_jack: @@ -58,3 +58,4 @@ - importantly it saves cognitive load but I expect skepticism, especially - since GHC would have to determine whether to interpret `show @Vector{}` to - `show @Vector`, `show @(Vector _n)` or `show @(Vector _n _a)`. + importantly it saves cognitive load but I expect raised eyebrows + (especially since GHC would have to determine whether to interpret `show + @Vector{}` to `show @Vector`, `show @(Vector _n)` or `show @(Vector _n + _a)`). New description: Use case: Visible type application. I often work with constructors with many arguments that I want to instantiate type variables with: {{{#!hs show @(Vector _ _) :: Show a => Vector n a -> String -- Type arguments reversed, see https://github.com/ekmett/distributive/pull/18 cotraverse @_ @(Vector _) :: (NATTY n, Functor f) => (f a -> b) -> (f (Vector n a) -> Vector n a') fmap @(Bazaar _ _ _) :: (t -> t') -> (Bazaar p a b t -> Bazaar p a b t') show @(Magma _ _ _ _) :: (Show a, Show i) => Magma i t b a -> String }}} This makes no sense since types have nothing to do with record or updates thereof but that syntax is often used to avoid parentheses and unneeded wildcard arguments: {{{#!hs isBar (Bar _ _ _ _ _) = True -- ===> isBar Bar{} = True }}} This also means you don't need to worry about the kind of your constructor wrt the type (class) variable it instantiates. ---- Thus the proposal is to allow: {{{#!hs show @Vector{} :: Show a => Vector n a -> String cotraverse @_ @Vector{} :: (NATTY n, Functor f) => (f a -> b) -> (f (Vector n a) -> Vector n a') fmap @Bazaar{} :: (t -> t') -> (Bazaar p a b t -> Bazaar p a b t') show @Magma{} :: (Show a, Show i) => Magma i t b a -> String }}} ---- This would save quite a few keystrokes in my daily coding but more importantly it saves cognitive load but I expect raised eyebrows (especially since GHC would have to determine whether to interpret `show @Vector{}` to `show @Vector`, `show @(Vector _n)` or `show @(Vector _n _a)`). -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12465#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler