definition module sem

import qualified Data.Map as Map
from Data.Either import :: Either
from AST import :: AST, :: Pos, :: Type, :: FieldSelector, :: Op2
from StdOverloaded import class toString

:: SemError 
	= ParseError Pos String 
	| UnifyError Pos Type Type 
    | FieldSelectorError Pos Type FieldSelector 
	| OperatorError Pos Op2 Type
	| Error String
:: Gamma
:: SemOutput :== Either [SemError] (AST, Gamma)

instance toString SemError
instance toString Gamma

sem :: AST -> SemOutput