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September 21, 2021 08:51
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{-# LANGUAGE Haskell2010 #-} | |
{-# LANGUAGE TemplateHaskell #-} | |
-- Used by QuasiQuote. Example taken from the GHC documentation. | |
module QuasiExpr where | |
import Language.Haskell.TH | |
import Language.Haskell.TH.Quote | |
data Expr = IntExpr Integer | |
| AntiIntExpr String | |
| BinopExpr BinOp Expr Expr | |
| AntiExpr String | |
deriving Show | |
data BinOp = AddOp | |
| SubOp | |
| MulOp | |
| DivOp | |
deriving Show | |
eval :: Expr -> Integer | |
eval (IntExpr n) = n | |
eval (BinopExpr op x y) = (opToFun op) (eval x) (eval y) | |
where | |
opToFun AddOp = (+) | |
opToFun SubOp = (-) | |
opToFun MulOp = (*) | |
opToFun DivOp = div | |
expr = QuasiQuoter parseExprExp undefined undefined undefined | |
-- cheating... | |
parseExprExp :: String -> Q Exp | |
parseExprExp _ = [| BinopExpr AddOp (IntExpr 1) (IntExpr 2) |] |
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{-# LANGUAGE Haskell2010 #-} | |
{-# LANGUAGE TemplateHaskell, QuasiQuotes #-} | |
-- example taken from the GHC documentation | |
module QuasiQuote where | |
import QuasiExpr | |
val :: Integer | |
val = eval [expr|1 + 2|] |
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