#5577: Two arguments are not two arguments according to the type checker
---------------------------------+------------------------------------------
Reporter: josef | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 7.0.3 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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I got a very strange type error message from GHC today. I've inserted it
at the end of this message. It is misleading because it complains that a
"lambda expression [...] has two arguments, but its type [...] has only
two". Now, I know that the code contains type errors but the error message
could be more helpful.
The code fragment which provokes this message looks as follows:
{{{
let writeElement = case ty of
Core.FloatType ->
\ix element -> tell [loc :!: ix := LitF element]
}}}
The `Core.FloatType` constructor is part of a GADT, the case ought to
refine the type of `element` to `Float`. I don't know if that's what's
tripping GHC up. The actual error has to do with the type of `ix` which
should be of type `Expr` but the function `writeElement` is applied to an
argument of type `Integer`.
The error message:
{{{
Couldn't match type `Expr' with `Integer'
The lambda expression `\ ix element -> tell ...' has two arguments,
but its type `Integer
-> b0
-> RWST () [Prog] Integer Data.Functor.Identity.Identity
c0'
has only two
In the expression:
\ ix element -> tell [loc :!: ix := LitF element]
In a case alternative:
Core.FloatType -> \ ix element -> tell [loc :!: ix := LitF
element]
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5577>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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