definition module sem

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

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

instance toString SemError
instance toString Gamma

sem :: AST -> SemOutput