Hello,
I have tried to compile a code like the following with GHC ...
==============================================
module Foo where
import MutableArray
import ByteArray
import ST
import PrelArrExtra
class Foo t where
foo :: t -> ByteArray ix
instance Ix ix => Foo (MutableByteArray s ix) where
foo x = runST(unsafeFreezeByteArray x)
-- in this context, foo converts a Mutable ByteArray to a
ByteArray
===============================================
... and the result of the compilation is the following error message
:
===============================================
Compilation Dump for: /usr/local/lib/ghc-4.08.1/hsc /tmp/ghc1047.cpp 2>>
erros -fglasgow-exts -fignore-interface-pragmas -fomit-interface-pragmas
-fsimplify [ -fmax-simplifier-iterations4 ]
-fwarn-overlapping-patterns -fwarn-missing-methods -fwarn-missing-fields
-fwarn-deprecations -fwarn-duplicate-exports -fhi-version=408 -static
"-himap=.%.hi:/usr/local/lib/ghc-4.08.1/imports/lang%.hi:/usr/local/lib/ghc-4.08.1/imports/lang%.hi:/usr/local/lib/ghc-4.08.1/imports/std%.hi"
"-himap-sep=:" -hifile=/tmp/ghc1047.hi -olang=asm
-ofile=/tmp/ghc1047.s -F=/tmp/ghc1047_stb.c -FH=/tmp/ghc1047_stb.h +RTS
-H6000000 -K1000000
duvida.hs:15:
Inferred type is less polymorphic than expected
Quantified type variable `s' escapes
It unifies with `s1', which is mentioned in the environment
The following variables in the environment mention `s1'
x :: MutableByteArray s1 ix
Signature type: forall s. ST s a
Type to generalise: ST s1 (ByteArray ix)
When checking an expression type signature
In the first argument of `runST', namely
`(unsafeFreezeByteArray x)'
In the right-hand side of an equation for `foo':
runST (unsafeFreezeByteArray x)
Compilation had errors
====================================================
I am trying to find a solution for making possible the "foo"
function to convert a MutableByteArray to a ByteArray in this context,
but without sucess.
How can I avoid this error in this code. Is it possible the foo
function to convert a MutableByteArray to a ByteArray in that context
??? I accept suggestions, some explanation about why this code is wrong
or some reference that can help me to find a solution ... :-)
F. Heron de Carvalho Jr.
