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module Evaluator (eval) where
import Control.Applicative ((*>))
import Control.Arrow ((&&&))
import Control.Monad.Except
import Environment
import Error.Base (LispError (..), LispResult (..),
unwrap)
import Operators
import Parser
import Text.ParserCombinators.Parsec
apply :: String -> [Expr] -> LispResult Expr
apply fn args = maybe
(throwError $ UnknownFunction fn)
($ args)
(lookup fn primitives)
evalUnquote :: Env -> Expr -> IOResult Expr
evalUnquote env (List [Id "unquote", vs]) = eval env vs
evalUnquote env (List [Id "quote", vs]) =
fmap (List . ([Id "quote"] ++ ) . (: [])) (evalUnquote env vs)
evalUnquote env (List vs) = List <$> mapM (evalUnquote env) vs
evalUnquote env (Vector vs) = Vector <$> mapM (evalUnquote env) vs
evalUnquote env literal = return literal
evalQuasiQuote :: Env -> Expr -> IOResult Expr
evalQuasiQuote env v@(Vector _) = evalUnquote env v
evalQuasiQuote env q@(List _) = evalUnquote env q -- list of atoms which may be quoted or unquoted
evalQuasiQuote env literal = return literal -- just behave like quote otherwise
eval :: Env -> Expr -> IOResult Expr
eval _ v@(StringLiteral s) = return v
eval _ v@(IntLiteral i) = return v
eval _ v@(BoolLiteral b) = return v
eval env (Id l) = getVar env l
eval _ v@(FloatLiteral f) = return v
eval env v@(Vector xs) = Vector <$> mapM (eval env) xs
eval env (List[Id "quote", val]) = return val
eval env (List[Id "quasiquote", val]) = evalQuasiQuote env val
eval env v@(List[Id "unquote", val]) = throwError $ BadForm "Cannot use `unquote` outside quasiquote form" v
eval env (List [Id "set!", Id var, val]) = eval env val >>= uncurry (*>) . (setVar env var &&& pure)
eval env (List [Id "define", Id var, val]) = eval env val >>= uncurry (*>) . (defineVar env var &&& pure)
eval env (List (Id fn : args)) = mapM (eval env) args >>= liftLispResult . apply fn
eval env NoReturn = throwError $ BadForm "Invalid usage of non-returning expression" NoReturn
-- handle bad forms
eval env invalidForm = throwError $ BadForm "lisk can't recognize this form" invalidForm
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