zot-0.0.1: src/SKI.hs

module SKI where

data Rec a
	= In { out :: Rec a -> Rec a }
	| Int { fromInt :: Int }
	| Char Char | Bool Bool
	| Error String

instance Eq ( Rec a ) where
	Int i == Int j		= i == j
	Char c == Char d	= c == d
	Bool b == Bool c	= b == c
	In _ == In _		= error "can not compare"
	_ == _			= False

instance Show ( Rec a ) where
	show ( Int i )		= show i
	show ( Error e )	= "Error: " ++ e
	show _			= "function"

suc :: Rec a
suc = In sc
	where
	sc ( Int i )	= Int $ succ i
	sc ( Char c )	= Char $ succ c
	sc _		= error "not int"

out_ x = case x of
	In f	-> f
	_	-> \y -> Error "not function"

oi :: Rec a -> Rec a
oi x = x
i = In oi

ok :: Rec a -> Rec a
ok x = In $ \_ -> x
k = In ok

os :: Rec a -> Rec a
-- s x y z = x z ( y z )
os x = In $ \y -> In $ \z -> ( out_ $ out_ x z ) ( out_ y z )
s = In os

readChurch :: Rec a -> Rec a
readChurch cn = cn `out_` suc `out_` ( Int 0 )

mkski = fst . makeSKI

makeSKI :: String -> ( Rec a, String )
makeSKI ( '`' : rest ) = let
	( c, rest' ) = makeSKI rest
	( c', rest'' ) = makeSKI rest' in case c of
		In f	-> ( f c', rest'' )
		_	-> ( Error "in makeSKI", rest'' )
--	( out c c', rest'' )
makeSKI ( 's' : rest ) = ( s, rest )
makeSKI ( 'k' : rest ) = ( k, rest )
makeSKI ( 'i' : rest ) = ( i, rest )

sc = mkski "`s``s`ks``s`kki"

mul x y = out ( out x ( out y sc ) ) ( out k i )