TemplateHaskell

Creating code at compile time

Example, creates a curry function for arbitrary large curry functions

module Curry
    (
        curryN
    ) where
 
import Control.Monad
import Language.Haskell.TH
 
curryN :: Int -> Q Exp
curryN n = do
    f  <- newName "f"
    xs <- replicateM n (newName "x")
    let args = map VarP (f:xs)
        ntup = TupE (map (pure . VarE) xs)
    return $ LamE args (AppE (VarE f) ntup)

Using the created code

Example, uses the curry function by using the placeholder `$(C.curryN 3)` that will be expanded by ghc

{-# LANGUAGE TemplateHaskell #-}
 
module Lib
    (
        someFunc
    ) where
 
import qualified Curry as C
 
someFunc :: IO ()
someFunc = 
    do
        print $ $(C.curryN 3) f1 1 ' ' ["Hallo"]
        print $ $(C.curryN 3) f1 1 '_' ["Hallo","world"]
        print $ $(C.curryN 3) f1 1 '.' ["Hallo","world","!"]
 
f1 :: (Int,Char,[String]) -> String
f1 (ni,ch,[]) = []
f1 (ni,ch,[s0]) = s0
f1 (ni,ch,s0:s1:rls) = s0 ++ replicate ni ch ++ f1 (ni,ch,s1:rls)

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TemplateHaskell

Creating code at compile time

Using the created code

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