Hi Simon,
On 6/4/07, Simon Peyton-Jones <[EMAIL PROTECTED]> wrote:
| Where typeApp splits a type to find its constructor, ctorTypes gets
| the types of the fields, and dataCtors gets the constructors in a data
| type. Unfortunately reify doesn't seem to work on types. Is it
| possible to do what I am after?
reify takes a Name, not a Type.
I am passing it a name, since I pattern match on the ConT:
let (ConT c, cs) = typeApp t
TyConI dat <- reify c
typeApp follows the AppT's to get a vector apply, so ConT is at the
very left of a chain on AppT.
Perhaps you mean that reify doesn't work on type constructors? (E.g. reify
''Maybe).
It should -- if you think it doesn't can you concoct a test case and submit it?
I'm not sure if I'm doing something wrong, as I haven't managed to get
it working for any type constructors. A test case:
ghci -fth
Prelude> :m Language.Haskell.TH
Language.Haskell.TH> $( reify (mkName "Maybe") >>= error . show )
Results in:
<interactive>:1:3:
`Maybe' is not in scope at a reify
In the expression:
$[splice]((reify (mkName "Maybe")) >>= (error . show))
In the definition of `it':
it = $[splice]((reify (mkName "Maybe")) >>= (error . show))
<interactive>:1:3:
Exception when trying to run compile-time code:
user error (IOEnv failure)
Code: let
>>= = (>>=) Q $dMonad
$dMonad = Language.Haskell.TH.Syntax.$f20
show = show Info $dShow
$dShow = Language.Haskell.TH.Syntax.$f60
in
(>>=) [Info, Exp]
(reify (mkName "Maybe"))
((.) [[Char], Q Exp, Info] (error (Q Exp)) show)
In the expression:
$[splice]((reify (mkName "Maybe")) >>= (error . show))
In the definition of `it':
it = $[splice]((reify (mkName "Maybe")) >>= (error . show))
The initial error is that Maybe is not in scope at reify. Changing to
"Data.Maybe.Maybe" doesn't help, trying "String" doesn't work,
creating a module and declaring a type in there then putting that
fragment in the file doesn't work.
Thanks
Neil
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