I have a function that accepts Type:
data MyType = IntT | BoolT | OtherT
typeToMyType :: Type -> MyType
How can I write a template that will indicate that I want to match the type Int?
What have i tried?
1
[t| GHC.Types.Int |]will create a type value Q Type, but despite the frequent fights, I could not get to merge with the template.
I tried to use it in the guard:
| $( do tI <- [t| GHC.Types.Int |]; [| t == tI |] ) = ...
But this complains:
No instance for (Language.Haskell.TH.Syntax.Lift Type)
arising from a use of `Language.Haskell.TH.Syntax.lift'
In the expression: Language.Haskell.TH.Syntax.lift tI
In a stmt of a 'do' block:
[| t == tI |]
pending(rn) [tI]
In the expression:
do { tI <- [t| Int |];
[| t == tI |]
pending(rn) [tI] }
2
Perhaps a simpler approach would be as follows:
typeToMyType :: Type -> MyType
typeToMyType (ConT $(''Int)) = NumberT
But then:
Couldn't match type `Name' with `Q Pat'
Expected type: PatQ
Actual type: Name
In the expression: ''Int
In the splice: $(''Int)
I have no idea what that means.
Why do I (even) need?
I want to parse the signature of the function to create Q Dec. I used Stringfor the prototype:
gen ["Int", "Int"] "luaOpMinus" '-
======>
Eval.hs:24:3-38
luaOpMinus [Number x_a98F, Number x_a98G]
= (return $ [Number ((-) x_a98F x_a98G)])
, Int -> Int -> Int, ["Int", "Int"] ( ), [LuaValue] -> LuaValue - , Lua . - , reify.
, , , reify :
Prelude Language.Haskell.TH Data.Bits> $(reify 'bit >>= stringE . show)
"ClassOpI Data.Bits.bit (ForallT [PlainTV a_1627400821] [ClassP Data.Bits.Bits [VarT a_1627400821]] (AppT (AppT
ArrowT (ConT GHC.Types.Int)) (VarT a_1627400821))) Data.Bits.Bits (Fixity 9 InfixL)"
(ConT GHC.Types.Int).