#9778: Namespace collision detection for promoted types -------------------------------------+------------------------------------- Reporter: crockeea | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.3 Component: Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Description changed by crockeea: Old description:
In the following example {{{#!hs {-# LANGUAGE DataKinds #-}
module Foo where
data Nat = Z | S Nat
data S
foo :: S n -> S n foo = id }}}
GHC displays the error
{{{ Foo.hs:12:8: ‘S’ is applied to too many type arguments In the type signature for ‘foo’: foo :: S n -> S n Failed, modules loaded: none. }}} Although it's clear in my example where the problem is, this example was distilled from a case where I imported module1 with type `S` defined and module2 with the promoted type `S`, which is what I was trying to use. Can we get namespace collision detection instead? Something like:
{{{ Foo.hs:9:15 Ambiguous occurence ‘S’ It could refer to either Foo.S defined at Foo.hs:7:1 or to the promoted constructor S defined at Foo.hs:5:16 Use 'S to refer to the promoted constructor. }}}
New description: In the following example {{{#!hs {-# LANGUAGE DataKinds #-} module Foo where data Nat = Z | S Nat data S foo :: S n -> S n foo = id }}} GHC displays the error {{{ Foo.hs:12:8: ‘S’ is applied to too many type arguments In the type signature for ‘foo’: foo :: S n -> S n Failed, modules loaded: none. }}} Of course this code compiles without the definition of `data S`. Without namespace collision detection, it is easy to have working code, and then import a module which breaks the code. For example, I made this request after I imported Module1 with type `S` defined and Module2 with the promoted type `S`, which is what I was trying to use. Can we get namespace collision detection instead? I'm proposing something like: {{{ Foo.hs:9:15 Ambiguous occurence ‘S’ It could refer to either Foo.S defined at Foo.hs:7:1 or to Foo.'S promoted from the constructor defined at Foo.hs:5:16 or to `Bar.'S` promoted from the constructor defined at Bar.hs:line#:char# or to ... Use 'S to refer to promoted constructors. }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9778#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler