Create a gist now

Instantly share code, notes, and snippets.

What would you like to do?
Example of Reification of AST.
{-# LANGUAGE OverloadedStrings,GADTs,FlexibleInstances #-}
import Data.List (intercalate)
import Data.Text (Text)
import qualified Data.Text as T
import qualified Data.Text.IO as T
type Ident = Text
-- 2D matrix
data Mat2D r = Mat Ident | MatConst [[r]]
class Scalar a
instance Scalar Int
instance Scalar Integer
instance Scalar Double
data Exp r where
Const :: (Reifiable r) => r -> Exp r
Add :: Exp r -> Exp r -> Exp r
Sub :: Exp r -> Exp r -> Exp r
Mul :: Exp r -> Exp r -> Exp r
Abs :: (Scalar r) => Exp r -> Exp r
Signum :: (Scalar r) => Exp r -> Exp r
Index2D :: (Num r) => Exp Int -> Exp Int -> Exp (Mat2D r) -> Exp r
instance (Scalar r) => Num (Exp (Mat2D r)) where
a + b = Add a b
a - b = Sub a b
a * b = Mul a b
-- Caution! abs, signum, fromInteger are not defined.
instance Num (Exp Int) where
a + b = Add a b
a - b = Sub a b
a * b = Mul a b
fromInteger a = Const (fromIntegral a)
-- Caution! abs and signum are not defined.
instance Num (Exp Double) where
a + b = Add a b
a - b = Sub a b
a * b = Mul a b
fromInteger a = Const (fromIntegral a)
-- Caution! abs and signum are not defined.
instance Num (Exp Integer) where
a + b = Add a b
a - b = Sub a b
a * b = Mul a b
fromInteger a = Const (fromIntegral a)
-- Caution! abs and signum are not defined.
class Reifiable a where
reify :: a -> Text
instance Reifiable (Exp r) where
reify (Const exp) = reify exp
reify (Add e1 e2) = T.concat [reify e1,"+",reify e2]
reify (Index2D i j mat) = T.concat [reify mat,"(",reify i,",",reify j,")"]
instance (Show r) => Reifiable (Mat2D r) where
reify (Mat ident) = ident
reify (MatConst xss) = T.pack $ "[" ++ intercalate ";" (map (intercalate " " . map show) xss) ++ "]"
instance Reifiable Int where
reify n = T.pack $ show n
instance Reifiable Integer where
reify n = T.pack $ show n
instance Reifiable Double where
reify n = T.pack $ show n
main = do
gen m1
gen test2
gen test3
gen test4
gen test5
gen :: Exp r -> IO ()
gen = T.putStrLn . reify
m1 :: Exp (Mat2D Int)
m1 = Const (MatConst [[1,2,3],[4,5,6]])
m2 :: Exp (Mat2D Int)
m2 = Const (MatConst [[10,5,3],[1,4,2]])
test4 :: Exp (Mat2D Int)
test4 = m1 + m1
test5 :: Exp (Mat2D Int)
test5 = foldl1 (+) (replicate 5 m1)
test2 :: Exp Int
test2 = Index2D 1 2 m1
test3 :: Exp Int
test3 = Index2D (Index2D 1 2 m1) 1 m2
{- Examples
*Main> main
[1 2 3;4 5 6]
[1 2 3;4 5 6](1,2)
[10 5 3;1 4 2]([1 2 3;4 5 6](1,2),1)
[1 2 3;4 5 6]+[1 2 3;4 5 6]
[1 2 3;4 5 6]+[1 2 3;4 5 6]+[1 2 3;4 5 6]+[1 2 3;4 5 6]+[1 2 3;4 5 6]
-}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment