Using Template Haskell to declare operators

THOp.hs

{-# LANGUAGE TemplateHaskell #-}

module THOp (mkOps) where

import Control.Monad

import Language.Haskell.TH

mkOp :: String -> Q [Dec]
mkOp n = [| $(varE a) + $(varE b) + length (filter (=='-') n) |] >>= \body ->
    return [FunD (mkName n) [Clause [VarP a, VarP b] (NormalB body) []]]
    where a = mkName "a"
          b = mkName "b"

mkOps :: Int -> Q [Dec]
mkOps n = fmap join $ mapM mkOp $ take n validOps

validOps :: [String]
validOps = fmap (('+':) . (++"+")) (iterate ('-':) "-")

THOpTest.hs

{-# LANGUAGE TemplateHaskell #-}

module THOpTest where

import THOp

mkOps 10

test1 :: IO ()
test1 = putStrLn $ "2 +---+ 3 == 8 : " ++ show (2 +---+ 3 == 8)

test2 :: IO ()
test2 = putStrLn $ "9 +-------+ 7 == 23 : " ++ show (9 +-------+ 7 == 23)