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module Haskell.Env where
import Control.Monad
import Data.List
import qualified Data.Map.Strict as Map
import Haskell.AST
data Env = Env { eDefs :: Map.Map Name Expr }
deriving (Show)
instance Pretty Env where
pretty (Env defs) =
intercalate "\n" [n ++ " = " ++ pretty e | (n, e) <- Map.assocs defs]
emptyEnv :: Env
emptyEnv = Env Map.empty
envFromAST :: AST -> Either String Env
envFromAST = addAST emptyEnv
addAST :: Env -> AST -> Either String Env
addAST env (AST tops) = foldM addTop env tops
addTop :: Env -> Toplevel -> Either String Env
addTop env (TopDef def) = addDef env def
addTop _ _ = Left "Only plain top-level definitions supported for the moment"
addDef :: Env -> Def -> Either String Env
addDef env (Def n ex) =
if envContains env n
then Left $ "Name '" ++ n ++ "' already present in environment"
else Right $ env { eDefs = Map.insert n ex (eDefs env) }
envContains :: Env -> Name -> Bool
envContains env name = Map.member name (eDefs env)
forget :: Env -> Name -> Either String Env
forget env name =
if envContains env name
then Right $ env { eDefs = Map.delete name (eDefs env) }
else Left $ "Name '" ++ name ++ "' not found in environment"
reAdd :: Env -> Def -> Either String Env
reAdd env def@(Def name _) = forget env name >>= flip addDef def
get :: Env -> Name -> Either String Expr
get env name = case Map.lookup name (eDefs env) of
Nothing -> Left "Name doesn't exist"
Just ex -> Right ex
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