#10708: Rejection of constant functions defined using conditional pattern matching -------------------------------------+------------------------------------- Reporter: HubertGaravel | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: invalid | Keywords: Operating System: Linux | Architecture: x86 Type of failure: GHC rejects | Test Case: valid program | Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by goldfire): * status: new => closed * resolution: => invalid Comment: I believe you mean the code to say this: {{{ data Nat = D0 | Succ Nat deriving (Show, Eq, Ord) d1 :: Nat d2 :: Nat d3 :: Nat d1 = (Succ D0) d2 | D0 == D0 = D0 d3 | D0 /= D0 = D0 | (Succ D0) == D0 = D0 | (Succ D0) /= D0 = (Succ D0) main = do print d1 print d2 print d3 }}} The name of a defined symbol is not repeated in the different branches. Thanks for reporting, however! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10708#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10708: Rejection of constant functions defined using conditional pattern matching -------------------------------------+------------------------------------- Reporter: HubertGaravel | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: invalid | Keywords: Operating System: Linux | Architecture: x86 Type of failure: GHC rejects | Test Case: valid program | Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by HubertGaravel): Thanks for your prompt answers. Yet, assuming that the definition of d3 is invalid because a funlhs must have at least one argument, why is the definition of d2 accepted in the example given? Like d3, d2 is defined by a conditional rule and is not followed by an argument. I assume that GHC processes lines fromp top to bottom and that if it complains about the definition of d3, it means that it finds the definition of d1 and d2 valid. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10708#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10708: Rejection of constant functions defined using conditional pattern matching -------------------------------------+------------------------------------- Reporter: HubertGaravel | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: invalid | Keywords: Operating System: Linux | Architecture: x86 Type of failure: GHC rejects | Test Case: valid program | Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by HubertGaravel): Thanks for the insight. If I try to reformulate, the definition of d3 is allowed by the syntax but forbidden by the static semantics. Perhaps the static semantics rule is too rigid and could be relaxed to make Haskell more regular. The example below shows that regularity is broken for arity 0 (empty pattern list). But I can live with this bizarre exception and will modify my Haskell generator to handle this corner case. Thanks again! Hubert {{{#!hs -- valid for arity 2 f2 x y | x == 0 = x f2 x y | x /= 0 = x + 1 -- valid for arity 1 f1 x | x == 0 = x f1 x | x /= 0 = x + 1 -- invalid for arity 0 f0 | 0 == 0 = 0 f0 | 0 /= 0 = 1 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10708#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler