[GHC] #12763: Incorrect behavior with empty functional dependencies
#12763: Incorrect behavior with empty functional dependencies -------------------------------------+------------------------------------- Reporter: diatchki | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is a corner case, but it would appear that GHC doesn't do proper improvements for classes with "empty" functional dependencies. Consider the following example: {{{#!hs class C a | -> a where m :: a -> () instance C Int f x = m x }}} The inferred type for `f` is `C a => a -> ()`, however I was expecting it to infer `Int -> ()`. The reasoning is as follows: the use of `m` generates a `C a` constraint (`a` is a unification variable). This should have interacted with the `C Int` instance (in a rather odd vacuous sort of way) to generate a derived constraint `a ~ Int`, which should have then instantiated `a` to `Int`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12763 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12763: Incorrect behavior with empty functional dependencies
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Reporter: diatchki | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type | Version: 8.0.1
checker) |
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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Comment (by Simon Peyton Jones
#12763: Incorrect behavior with empty functional dependencies -------------------------------------+------------------------------------- Reporter: diatchki | Owner: Type: bug | Status: merge Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_compile/T12763 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => merge * testcase: => typecheck/should_compile/T12763 Comment: Fixed thank you. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12763#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12763: Incorrect behavior with empty functional dependencies -------------------------------------+------------------------------------- Reporter: diatchki | Owner: Type: bug | Status: merge Priority: normal | Milestone: 8.0.2 Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_compile/T12763 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * milestone: => 8.0.2 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12763#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12763: Incorrect behavior with empty functional dependencies -------------------------------------+------------------------------------- Reporter: diatchki | Owner: Type: bug | Status: closed Priority: normal | Milestone: 8.0.2 Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_compile/T12763 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed * resolution: => fixed Comment: Merged to `ghc-8.0` as 8719d871bac848ee10e7455b5821a18dabd48b5b. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12763#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12763: Incorrect behavior with empty functional dependencies -------------------------------------+------------------------------------- Reporter: diatchki | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.0.2 Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: fixed | Keywords: FunDeps Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_compile/T12763 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => FunDeps -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12763#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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