husk-scheme-2.0: hs-src/Scheme/Core.hs
{-
- husk scheme interpreter
-
- A lightweight dialect of R5RS scheme.
- This file contains Core functionality, primarily Scheme expression evaluation.
-
- @author Justin Ethier
-
- -}
module Scheme.Core
(
eval
, evalLisp
, evalString
, evalAndPrint
, primitiveBindings -- FUTURE: this may be a bad idea...
-- but there should be an interface to inject custom functions written in Haskell
) where
import Scheme.Macro
import Scheme.Numerical
import Scheme.Parser
import Scheme.Types
import Scheme.Variables
import Control.Monad.Error
import Char
import Data.Array
import qualified Data.Map
import Maybe
import List
import IO hiding (try)
--import Debug.Trace
{-| Evaluate a string containing Scheme code.
For example:
@
env <- primitiveBindings
evalString env "(+ x x x)"
"3"
evalString env "(+ x x x (* 3 9))"
"30"
evalString env "(* 3 9)"
"27"
@
-}
evalString :: Env -> String -> IO String
evalString env expr = runIOThrows $ liftM show $ (liftThrows $ readExpr expr) >>= macroEval env >>= (eval env (makeNullContinuation env))
-- |Evaluate a string and print results to console
evalAndPrint :: Env -> String -> IO ()
evalAndPrint env expr = evalString env expr >>= putStrLn --TODO: cont parameter
-- |Evaluate lisp code that has already been loaded into haskell
--
-- TODO: code example for this, via ghci and/or a custom program.
evalLisp :: Env -> LispVal -> IOThrowsError LispVal
evalLisp env lisp = macroEval env lisp >>= (eval env (makeNullContinuation env))
{- continueEval is a support function for eval, below.
-
- Transformed eval section into CPS by calling into this instead of returning from eval.
- This function uses the cont argument to determine whether to keep going or to finally
- return a result.
- -}
continueEval :: Env -> LispVal -> LispVal -> IOThrowsError LispVal
-- Passing a higher-order function as the continuation; just evaluate it. This is
-- done to enable an 'eval' function to be broken up into multiple sub-functions,
-- so that any of the sub-functions can be passed around as a continuation.
--
-- This perhaps shows cruft as we also pass cBody (scheme code) as a continuation.
-- We could probably just use higher-order functions instead, but both are used for
-- two different things.
continueEval _ (Continuation cEnv _ cCont funcArgs (Just func)) val = func cEnv cCont val funcArgs
-- No higher order function, so:
--
-- If there is Scheme code to evaluate in the function body, we continue to evaluate it.
--
-- Otherwise, if all code in the function has been executed, we 'unwind' to an outer
-- continuation (if there is one), or we just return the result. Yes technically with
-- CPS you are supposed to keep calling into functions and never return, but eventually
-- when the computation is complete, you have to return something.
continueEval _ (Continuation cEnv cBody cCont Nothing Nothing) val = do
case cBody of
[] -> do
case cCont of
Continuation nEnv _ _ _ _ -> continueEval nEnv cCont val
_ -> return (val)
[lv] -> eval cEnv (Continuation cEnv [] cCont Nothing Nothing) (lv)
(lv : lvs) -> eval cEnv (Continuation cEnv lvs cCont Nothing Nothing) (lv)
continueEval _ _ _ = throwError $ Default "Internal error in continueEval"
-- |Core eval function
-- Evaluate a scheme expression.
-- NOTE: This function does not include macro support and should not be called directly. Instead, use 'evalLisp'
--
--
-- Implementation Notes:
--
-- Internally, this function is written in continuation passing style (CPS) to allow the Scheme language
-- itself to support first-class continuations. That is, at any point in the evaluation, call/cc may
-- be used to capture the current continuation. Thus this code must call into the next continuation point, eg:
--
-- eval ... (makeCPS ...)
--
-- Instead of calling eval directly from within the same function, eg:
--
-- eval ...
-- eval ...
--
-- This can make the code harder to follow, however some coding conventions have been established to make the
-- code easier to follow. Whenever a single function has been broken into multiple ones for the purpose of CPS,
-- those additional functions are defined locally using 'where', and each has been given a 'cps' prefix.
--
eval :: Env -> LispVal -> LispVal -> IOThrowsError LispVal
eval env cont val@(Nil _) = continueEval env cont val
eval env cont val@(String _) = continueEval env cont val
eval env cont val@(Char _) = continueEval env cont val
eval env cont val@(Complex _) = continueEval env cont val
eval env cont val@(Float _) = continueEval env cont val
eval env cont val@(Rational _) = continueEval env cont val
eval env cont val@(Number _) = continueEval env cont val
eval env cont val@(Bool _) = continueEval env cont val
eval env cont val@(HashTable _) = continueEval env cont val
eval env cont val@(Vector _) = continueEval env cont val
eval env cont (Atom a) = continueEval env cont =<< getVar env a
eval env cont (List [Atom "quote", val]) = continueEval env cont val
-- Unquote an expression; unquoting is different than quoting in that
-- it may also be inter-spliced with code that is meant to be evaluated.
eval envi cont (List [Atom "quasiquote", value]) = cpsUnquote envi cont value Nothing
where cpsUnquote :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsUnquote e c val _ = do
case val of
List [Atom "unquote", vval] -> eval e c vval
List (_ : _) -> doCpsUnquoteList e c val
DottedList xs x -> do
doCpsUnquoteList e (makeCPSWArgs e c cpsUnquotePair $ [x] ) $ List xs
Vector vec -> do
let len = length (elems vec)
doCpsUnquoteList e (makeCPSWArgs e c cpsUnquoteVector $ [Number $ toInteger len]) $ List $ elems vec
_ -> eval e c (List [Atom "quote", val]) -- Behave like quote if there is nothing to "unquote"...
-- Unquote a pair
-- This must be started by unquoting the "left" hand side of the pair,
-- then pass a continuation to this function to unquote the right-hand side (RHS).
-- This function does the RHS and then calls into a continuation to finish the pair.
cpsUnquotePair :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsUnquotePair e c (List rxs) (Just [rx]) = do
cpsUnquote e (makeCPSWArgs e c cpsUnquotePairFinish $ [List rxs]) rx Nothing
cpsUnquotePair _ _ _ _ = throwError $ InternalError "Unexpected parameters to cpsUnquotePair"
-- Finish unquoting a pair by combining both of the unquoted left/right hand sides.
cpsUnquotePairFinish :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsUnquotePairFinish e c rx (Just [List rxs]) = do
case rx of
List [] -> continueEval e c $ List rxs
List rxlst -> continueEval e c $ List $ rxs ++ rxlst
DottedList rxlst rxlast -> continueEval e c $ DottedList (rxs ++ rxlst) rxlast
_ -> continueEval e c $ DottedList rxs rx
cpsUnquotePairFinish _ _ _ _ = throwError $ InternalError "Unexpected parameters to cpsUnquotePairFinish"
-- Unquote a vector
cpsUnquoteVector :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsUnquoteVector e c (List vList) (Just [Number len]) = continueEval e c (Vector $ listArray (0, fromInteger len) vList)
cpsUnquoteVector _ _ _ _ = throwError $ InternalError "Unexpected parameters to cpsUnquoteVector"
-- Front-end to cpsUnquoteList, to encapsulate default values in the call
doCpsUnquoteList :: Env -> LispVal -> LispVal -> IOThrowsError LispVal
doCpsUnquoteList e c (List (x:xs)) = cpsUnquoteList e c x $ Just ([List xs, List []])
doCpsUnquoteList _ _ _ = throwError $ InternalError "Unexpected parameters to doCpsUnquoteList"
-- Unquote a list
cpsUnquoteList :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsUnquoteList e c val (Just ([List unEvaled, List acc])) = do
case val of
List [Atom "unquote-splicing", vvar] -> do
eval e (makeCPSWArgs e c cpsUnquoteSplicing $ [List unEvaled, List acc]) vvar
_ -> cpsUnquote e (makeCPSWArgs e c cpsUnquoteFld $ [List unEvaled, List acc]) val Nothing
cpsUnquoteList _ _ _ _ = throwError $ InternalError "Unexpected parameters to cpsUnquoteList"
-- Evaluate an expression instead of quoting it
cpsUnquoteSplicing :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsUnquoteSplicing e c val (Just ([List unEvaled, List acc])) = do
case val of
List v -> case unEvaled of
[] -> continueEval e c $ List $ acc ++ v
_ -> cpsUnquoteList e c (head unEvaled) (Just [List (tail unEvaled), List $ acc ++ v ])
_ -> throwError $ TypeMismatch "proper list" val
cpsUnquoteSplicing _ _ _ _ = throwError $ InternalError "Unexpected parameters to cpsUnquoteSplicing"
-- Unquote processing for single field of a list
cpsUnquoteFld :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsUnquoteFld e c val (Just ([List unEvaled, List acc])) = do
case unEvaled of
[] -> continueEval e c $ List $ acc ++ [val]
_ -> cpsUnquoteList e c (head unEvaled) (Just [List (tail unEvaled), List $ acc ++ [val] ])
cpsUnquoteFld _ _ _ _ = throwError $ InternalError "Unexpected parameters to cpsUnquoteFld"
eval env cont (List [Atom "if", predic, conseq, alt]) = do
eval env (makeCPS env cont cps) (predic)
where cps :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cps e c result _ =
case (result) of
Bool False -> eval e c alt
_ -> eval e c conseq
eval env cont (List [Atom "if", predic, conseq]) =
eval env (makeCPS env cont cpsResult) predic
where cpsResult :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsResult e c result _ =
case result of
Bool True -> eval e c conseq
_ -> continueEval e c $ Atom "#unspecified" -- Unspecified return value per R5RS
-- FUTURE: convert cond to a derived form (scheme macro)
eval env cont (List (Atom "cond" : clauses)) =
if length clauses == 0
then throwError $ BadSpecialForm "No matching clause" $ String "cond"
else do
case (clauses !! 0) of
List (Atom "else" : _) -> eval env (makeCPSWArgs env cont cpsResult clauses) $ Bool True
List (cond : _) -> eval env (makeCPSWArgs env cont cpsResult clauses) cond
badType -> throwError $ TypeMismatch "clause" badType
where cpsResult :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsResult e cnt result (Just (c:cs)) =
case result of
Bool True -> evalCond e cnt c
_ -> eval env cnt $ List $ (Atom "cond" : cs)
cpsResult _ _ _ _ = throwError $ Default "Unexpected error in cond"
-- Helper function for evaluating 'cond'
evalCond :: Env -> LispVal -> LispVal -> IOThrowsError LispVal
evalCond e c (List [_, expr]) = eval e c expr
evalCond e c (List (_ : expr)) = eval e c $ List (Atom "begin" : expr)
evalCond _ _ badForm = throwError $ BadSpecialForm "evalCond: Unrecognized special form" badForm
eval env cont (List (Atom "begin" : funcs)) =
if length funcs == 0
then eval env cont $ Nil ""
else if length funcs == 1
then eval env cont (head funcs)
else eval env (makeCPSWArgs env cont cpsRest $ tail funcs) (head funcs)
where cpsRest :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsRest e c _ args =
case args of
Just fArgs -> eval e c $ List (Atom "begin" : fArgs)
Nothing -> throwError $ Default "Unexpected error in begin"
-- TODO: rewrite in CPS (??)
eval env cont (List [Atom "load", String filename]) = do
-- load filename >>= liftM last . mapM (evaluate env cont)
result <- load filename >>= liftM last . mapM (evaluate env (makeNullContinuation env))
continueEval env cont result
where evaluate env2 cont2 val2 = macroEval env2 val2 >>= eval env2 cont2
eval env cont (List [Atom "set!", Atom var, form]) = do
eval env (makeCPS env cont cpsResult) form
where cpsResult :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsResult e c result _ = setVar e var result >>= continueEval e c
eval env cont (List [Atom "define", Atom var, form]) = do
eval env (makeCPS env cont cpsResult) form
where cpsResult :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsResult e c result _ = defineVar e var result >>= continueEval e c
eval env cont (List (Atom "define" : List (Atom var : fparams) : fbody )) = do
result <- (makeNormalFunc env fparams fbody >>= defineVar env var)
continueEval env cont result
eval env cont (List (Atom "define" : DottedList (Atom var : fparams) varargs : fbody)) = do
result <- (makeVarargs varargs env fparams fbody >>= defineVar env var)
continueEval env cont result
eval env cont (List (Atom "lambda" : List fparams : fbody)) = do
result <- makeNormalFunc env fparams fbody
continueEval env cont result
eval env cont (List (Atom "lambda" : DottedList fparams varargs : fbody)) = do
result <- makeVarargs varargs env fparams fbody
continueEval env cont result
eval env cont (List (Atom "lambda" : varargs@(Atom _) : fbody)) = do
result <- makeVarargs varargs env [] fbody
continueEval env cont result
eval env cont (List [Atom "string-fill!", Atom var, character]) = do
eval env (makeCPS env cont cpsVar) =<< getVar env var
where cpsVar :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsVar e c result _ = eval e (makeCPSWArgs e c cpsChr $ [result]) $ character
cpsChr :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsChr e c result (Just [rVar]) = (fillStr(rVar, result) >>= setVar e var) >>= continueEval e c
cpsChr _ _ _ _ = throwError $ Default "Unexpected error in string-fill!"
fillStr (String str, Char achr) = doFillStr (String "", Char achr, length str)
fillStr (String _, c) = throwError $ TypeMismatch "character" c
fillStr (s, _) = throwError $ TypeMismatch "string" s
doFillStr (String str, Char achr, left) = do
if left == 0
then return $ String str
else doFillStr(String $ achr : str, Char achr, left - 1)
doFillStr (String _, c, _) = throwError $ TypeMismatch "character" c
doFillStr (s, Char _, _) = throwError $ TypeMismatch "string" s
doFillStr (_, _, _) = throwError $ BadSpecialForm "Unexpected error in string-fill!" $ List []
eval env cont (List [Atom "string-set!", Atom var, i, character]) = do
eval env (makeCPS env cont cpsStr) i
where
cpsStr :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsStr e c idx _ = eval e (makeCPSWArgs e c cpsSubStr $ [idx]) =<< getVar e var
cpsSubStr :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsSubStr e c str (Just [idx]) =
substr(str, character, idx) >>= setVar e var >>= continueEval e c
cpsSubStr _ _ _ _ = throwError $ InternalError "Invalid argument to cpsSubStr"
substr (String str, Char char, Number ii) = do
return $ String $ (take (fromInteger ii) . drop 0) str ++
[char] ++
(take (length str) . drop (fromInteger ii + 1)) str
substr (String _, Char _, n) = throwError $ TypeMismatch "number" n
substr (String _, c, _) = throwError $ TypeMismatch "character" c
substr (s, _, _) = throwError $ TypeMismatch "string" s
eval env cont (List [Atom "set-cdr!", Atom var, argObj]) = do
-- eval env (makeCPS env cont cpsObj) =<< getVar env var
continueEval env (makeCPS env cont cpsObj) =<< getVar env var
where
cpsObj :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsObj _ _ pair@(List []) _ = throwError $ TypeMismatch "pair" pair
cpsObj e c pair@(List (_:_)) _ = eval e (makeCPSWArgs e c cpsSet $ [pair]) argObj
cpsObj e c pair@(DottedList _ _) _ = eval e (makeCPSWArgs e c cpsSet $ [pair]) argObj
cpsObj _ _ pair _ = throwError $ TypeMismatch "pair" pair
cpsSet :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsSet e c obj (Just [List (l : _)]) = setVar e var (DottedList [l] obj) >>= continueEval e c
cpsSet e c obj (Just [DottedList (l : _) _]) = setVar e var (DottedList [l] obj) >>= continueEval e c
cpsSet _ _ _ _ = throwError $ InternalError "Unexpected argument to cpsSet"
eval env cont (List [Atom "vector-set!", Atom var, i, object]) = do
eval env (makeCPS env cont cpsObj) i
where
cpsObj :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsObj e c idx _ = eval e (makeCPSWArgs e c cpsVec $ [idx]) object
cpsVec :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsVec e c obj (Just [idx]) = eval e (makeCPSWArgs e c cpsUpdateVec $ [idx, obj]) =<< getVar e var
cpsVec _ _ _ _ = throwError $ InternalError "Invalid argument to cpsVec"
cpsUpdateVec :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsUpdateVec e c vec (Just [idx, obj]) =
updateVector vec idx obj >>= setVar e var >>= continueEval e c
cpsUpdateVec _ _ _ _ = throwError $ InternalError "Invalid argument to cpsUpdateVec"
updateVector :: LispVal -> LispVal -> LispVal -> IOThrowsError LispVal
updateVector (Vector vec) (Number idx) obj = return $ Vector $ vec//[(fromInteger idx, obj)]
updateVector v _ _ = throwError $ TypeMismatch "vector" v
eval env cont (List [Atom "vector-fill!", Atom var, object]) = do
eval env (makeCPS env cont cpsVec) object
where
cpsVec :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsVec e c obj _ = eval e (makeCPSWArgs e c cpsFillVec $ [obj]) =<< getVar e var
cpsFillVec :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsFillVec e c vec (Just [obj]) =
fillVector vec obj >>= setVar e var >>= continueEval e c
cpsFillVec _ _ _ _ = throwError $ InternalError "Invalid argument to cpsFillVec"
fillVector :: LispVal -> LispVal -> IOThrowsError LispVal
fillVector (Vector vec) obj = do
let l = replicate (lenVector vec) obj
return $ Vector $ (listArray (0, length l - 1)) l
fillVector v _ = throwError $ TypeMismatch "vector" v
lenVector v = length (elems v)
eval env cont (List [Atom "hash-table-set!", Atom var, rkey, rvalue]) = do
eval env (makeCPS env cont cpsValue) rkey
where
cpsValue :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsValue e c key _ = eval e (makeCPSWArgs e c cpsH $ [key]) rvalue
cpsH :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsH e c value (Just [key]) = eval e (makeCPSWArgs e c cpsEvalH $ [key, value]) =<< getVar e var
cpsH _ _ _ _ = throwError $ InternalError "Invalid argument to cpsH"
cpsEvalH :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsEvalH e c h (Just [key, value]) = do
case h of
HashTable ht -> do
setVar env var (HashTable $ Data.Map.insert key value ht) >>= eval e c
other -> throwError $ TypeMismatch "hash-table" other
cpsEvalH _ _ _ _ = throwError $ InternalError "Invalid argument to cpsEvalH"
eval env cont (List [Atom "hash-table-delete!", Atom var, rkey]) = do
eval env (makeCPS env cont cpsH) rkey
where
cpsH :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsH e c key _ = eval e (makeCPSWArgs e c cpsEvalH $ [key]) =<< getVar e var
cpsEvalH :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsEvalH e c h (Just [key]) = do
case h of
HashTable ht -> do
setVar env var (HashTable $ Data.Map.delete key ht) >>= eval e c
other -> throwError $ TypeMismatch "hash-table" other
cpsEvalH _ _ _ _ = throwError $ InternalError "Invalid argument to cpsEvalH"
-- TODO:
-- hash-table-merge!
eval _ _ (List [Atom "apply"]) = throwError $ BadSpecialForm "apply" $ String "Function not specified"
eval _ _ (List [Atom "apply", _]) = throwError $ BadSpecialForm "apply" $ String "Arguments not specified"
eval env cont (List (Atom "apply" : applyArgs)) = do
eval env (makeCPSWArgs env cont cpsLast $ [List applyArgs]) $ head applyArgs
where cpsLast :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsLast e c proc (Just [List args]) =
eval e (makeCPSWArgs e c cpsArgs $ [proc, List $ tail $ reverse $ tail $ reverse args]) $ head $ reverse args
cpsLast _ _ _ _ = throwError $ InternalError "Invalid arguments to cpsLast"
cpsArgs :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsArgs e c lst (Just [proc, List args]) =
case args of
[] -> cpsApply c (Just [proc, lst, List args])
_ -> eval e (makeCPSWArgs e c cpsEvalArgs $ [proc, lst, List $ tail args, List []]) $ head args
cpsArgs _ _ _ _ = throwError $ InternalError "Invalid arguments to cpsArgs"
cpsEvalArgs :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsEvalArgs e c result (Just [proc, lst, List args, List evaledArgs]) =
case args of
[] -> cpsApply c (Just [proc, lst, List (evaledArgs ++ [result])])
(x:xs) -> eval e (makeCPSWArgs e c cpsEvalArgs $ [proc, lst, List xs, List (evaledArgs ++ [result])]) x
cpsEvalArgs _ _ _ _ = throwError $ InternalError "Invalid arguments to cpsEvalArgs"
cpsApply :: LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsApply c (Just [proc, lst, List argVals]) = do
case lst of
List l -> apply c proc (argVals ++ l)
other -> throwError $ TypeMismatch "list" other
cpsApply _ _ = throwError $ InternalError "Invalid arguments to cpsApply"
eval env cont (List (Atom "call-with-current-continuation" : args)) =
eval env cont (List (Atom "call/cc" : args))
eval _ _ (List [Atom "call/cc"]) = throwError $ Default "Procedure not specified"
eval env cont (List [Atom "call/cc", proc]) = do
func <- eval env (makeNullContinuation env) proc -- TODO: Use CPS here instead????
case func of
PrimitiveFunc f -> do
result <- liftThrows $ f [cont]
case cont of
Continuation cEnv _ _ _ _ -> continueEval cEnv cont result
_ -> return result
Func aparams _ _ _ ->
if (toInteger $ length aparams) == 1
then apply cont func [cont]
else throwError $ NumArgs (toInteger $ length aparams) [cont]
other -> throwError $ TypeMismatch "procedure" other
-- Call a function by evaluating its arguments and then
-- executing it via 'apply'.
eval env cont (List (function : functionArgs)) = do
eval env (makeCPSWArgs env cont cpsPrepArgs $ functionArgs) function
where cpsPrepArgs :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsPrepArgs e c func (Just args) =
-- case (trace ("prep eval of args: " ++ show args) args) of
case (args) of
[] -> apply c func [] -- No args, immediately apply the function
[a] -> eval env (makeCPSWArgs e c cpsEvalArgs $ [func, List [], List []]) a
(a:as) -> eval env (makeCPSWArgs e c cpsEvalArgs $ [func, List [], List as]) a
cpsPrepArgs _ _ _ Nothing = throwError $ Default "Unexpected error in function application (1)"
-- Store value of previous argument, evaluate the next arg until all are done
-- parg - Previous argument that has now been evaluated
-- state - List containing the following, in order:
-- - Function to apply when args are ready
-- - List of evaluated parameters
-- - List of parameters awaiting evaluation
cpsEvalArgs :: Env -> LispVal -> LispVal -> Maybe [LispVal] -> IOThrowsError LispVal
cpsEvalArgs e c evaledArg (Just [func, List argsEvaled, List argsRemaining]) =
case argsRemaining of
[] -> apply c func (argsEvaled ++ [evaledArg])
[a] -> eval e (makeCPSWArgs e c cpsEvalArgs $ [func, List (argsEvaled ++ [evaledArg]), List []]) a
(a:as) -> eval e (makeCPSWArgs e c cpsEvalArgs $ [func, List (argsEvaled ++ [evaledArg]), List as]) a
cpsEvalArgs _ _ _ (Just _) = throwError $ Default "Unexpected error in function application (1)"
cpsEvalArgs _ _ _ Nothing = throwError $ Default "Unexpected error in function application (2)"
eval _ _ badForm = throwError $ BadSpecialForm "Unrecognized special form" badForm
makeFunc :: --forall (m :: * -> *).
(Monad m) =>
Maybe String -> Env -> [LispVal] -> [LispVal] -> m LispVal
makeFunc varargs env fparams fbody = return $ Func (map showVal fparams) varargs fbody env
makeNormalFunc :: (Monad m) => Env
-> [LispVal]
-> [LispVal]
-> m LispVal
makeNormalFunc = makeFunc Nothing
makeVarargs :: (Monad m) => LispVal -> Env
-> [LispVal]
-> [LispVal]
-> m LispVal
makeVarargs = makeFunc . Just . showVal
-- Call into a Scheme function
apply :: LispVal -> LispVal -> [LispVal] -> IOThrowsError LispVal
apply _ c@(Continuation env _ _ _ _) args = do
if (toInteger $ length args) /= 1
then throwError $ NumArgs 1 args
else continueEval env c $ head args
apply cont (IOFunc func) args = do
result <- func args
case cont of
Continuation cEnv _ _ _ _ -> continueEval cEnv cont result
_ -> return result
apply cont (PrimitiveFunc func) args = do
result <- liftThrows $ func args
case cont of
Continuation cEnv _ _ _ _ -> continueEval cEnv cont result
_ -> return result
apply cont (Func aparams avarargs abody aclosure) args =
if num aparams /= num args && avarargs == Nothing
then throwError $ NumArgs (num aparams) args
else (liftIO $ extendEnv aclosure $ zip (map ((,) varNamespace) aparams) args) >>= bindVarArgs avarargs >>= (evalBody abody)
where remainingArgs = drop (length aparams) args
num = toInteger . length
--
-- Continue evaluation within the body, preserving the outer continuation.
--
-- This link was helpful for implementing this, and has a *lot* of other useful information:
-- http://icem-www.folkwang-hochschule.de/~finnendahl/cm_kurse/doc/schintro/schintro_73.html#SEC80
--
-- What we are doing now is simply not saving a continuation for tail calls. For now this may
-- be good enough, although it may need to be enhanced in the future in order to properly
-- detect all tail calls.
--
-- See: http://icem-www.folkwang-hochschule.de/~finnendahl/cm_kurse/doc/schintro/schintro_142.html#SEC294
--
evalBody evBody env = case cont of
Continuation _ cBody cCont _ Nothing -> if length cBody == 0
then continueWCont env (evBody) cCont
else continueWCont env (evBody) cont -- Might be a problem, not fully optimizing
_ -> continueWCont env (evBody) cont
-- Shortcut for calling continueEval
continueWCont cwcEnv cwcBody cwcCont =
continueEval cwcEnv (Continuation cwcEnv cwcBody cwcCont Nothing Nothing) $ Nil ""
bindVarArgs arg env = case arg of
Just argName -> liftIO $ extendEnv env [((varNamespace, argName), List $ remainingArgs)]
Nothing -> return env
apply _ func args = throwError $ BadSpecialForm "Unable to evaluate form" $ List (func : args)
-- |Environment containing the primitive forms that are built into the Scheme language. Note that this only includes
-- forms that are implemented in Haskell; derived forms implemented in Scheme (such as let, list, etc) are available
-- in the standard library which must be pulled into the environment using (load).
primitiveBindings :: IO Env
primitiveBindings = nullEnv >>= (flip extendEnv $ map (domakeFunc IOFunc) ioPrimitives
++ map (domakeFunc PrimitiveFunc) primitives)
where domakeFunc constructor (var, func) = ((varNamespace, var), constructor func)
ioPrimitives :: [(String, [LispVal] -> IOThrowsError LispVal)]
ioPrimitives = [("open-input-file", makePort ReadMode),
("open-output-file", makePort WriteMode),
("close-input-port", closePort),
("close-output-port", closePort),
("read", readProc),
("write", writeProc),
("read-contents", readContents),
("read-all", readAll)]
makePort :: IOMode -> [LispVal] -> IOThrowsError LispVal
makePort mode [String filename] = liftM Port $ liftIO $ openFile filename mode
makePort _ [] = throwError $ NumArgs 1 []
makePort _ args@(_ : _) = throwError $ NumArgs 1 args
closePort :: [LispVal] -> IOThrowsError LispVal
closePort [Port port] = liftIO $ hClose port >> (return $ Bool True)
closePort _ = return $ Bool False
readProc :: [LispVal] -> IOThrowsError LispVal
readProc [] = readProc [Port stdin]
readProc [Port port] = (liftIO $ hGetLine port) >>= liftThrows . readExpr
readProc args@(_ : _) = throwError $ BadSpecialForm "" $ List args
writeProc :: [LispVal] -> IOThrowsError LispVal
writeProc [obj] = writeProc [obj, Port stdout]
writeProc [obj, Port port] = liftIO $ hPrint port obj >> (return $ Nil "")
writeProc other = if length other == 2
then throwError $ TypeMismatch "(value port)" $ List other
else throwError $ NumArgs 2 other
readContents :: [LispVal] -> IOThrowsError LispVal
readContents [String filename] = liftM String $ liftIO $ readFile filename
readContents [] = throwError $ NumArgs 1 []
readContents args@(_ : _) = throwError $ NumArgs 1 args
load :: String -> IOThrowsError [LispVal]
load filename = (liftIO $ readFile filename) >>= liftThrows . readExprList
-- TODO: load should not crash interpreter if file does not exist
readAll :: [LispVal] -> IOThrowsError LispVal
readAll [String filename] = liftM List $ load filename
readAll [] = throwError $ NumArgs 1 []
readAll args@(_ : _) = throwError $ NumArgs 1 args
primitives :: [(String, [LispVal] -> ThrowsError LispVal)]
primitives = [("+", numAdd),
("-", numSub),
("*", numMul),
("/", numDiv),
("modulo", numericBinop mod),
("quotient", numericBinop quot),
("remainder", numericBinop rem),
("round", numRound),
("floor", numFloor),
("ceiling", numCeiling),
("truncate", numTruncate),
("numerator", numNumerator),
("denominator", numDenominator),
("exp", numExp),
("log", numLog),
("sin", numSin),
("cos", numCos),
("tan", numTan),
("asin", numAsin),
("acos", numAcos),
("atan", numAtan),
("sqrt", numSqrt),
("expt", numExpt),
("make-rectangular", numMakeRectangular),
("make-polar", numMakePolar),
("real-part", numRealPart ),
("imag-part", numImagPart),
("magnitude", numMagnitude),
("angle", numAngle ),
("exact->inexact", numExact2Inexact),
("inexact->exact", numInexact2Exact),
("number->string", num2String),
("=", numBoolBinopEq),
(">", numBoolBinopGt),
(">=", numBoolBinopGte),
("<", numBoolBinopLt),
("<=", numBoolBinopLte),
-- TODO: sweep through the spec to make sure all numeric procedures are accounted for
-- TODO: sweep through spec and implement all numeric "library procedures" - but in stdlib.scm
-- TODO: string and number conversion functions; need to make
-- sure they are implemented and that they handle the full tower
("&&", boolBoolBinop (&&)),
("||", boolBoolBinop (||)),
("string=?", strBoolBinop (==)),
("string<?", strBoolBinop (<)),
("string>?", strBoolBinop (>)),
("string<=?", strBoolBinop (<=)),
("string>=?", strBoolBinop (>=)),
("string-ci=?", stringCIEquals),
("string-ci<?", stringCIBoolBinop (<)),
("string-ci>?", stringCIBoolBinop (>)),
("string-ci<=?", stringCIBoolBinop (<=)),
("string-ci>=?", stringCIBoolBinop (>=)),
("car", car),
("cdr", cdr),
("cons", cons),
("eq?", eqv),
("eqv?", eqv),
("equal?", equal),
("pair?", isDottedList),
("procedure?", isProcedure),
{-
TODO: full numeric tower: number?, complex?, rational?
--}
("number?", isNumber),
("complex?", isComplex),
("real?", isReal),
("rational?", isRational),
("integer?", isInteger),
("list?", unaryOp isList),
("null?", isNull),
("symbol?", isSymbol),
("symbol->string", symbol2String),
("string->symbol", string2Symbol),
("char?", isChar),
("vector?", unaryOp isVector),
("make-vector", makeVector),
("vector", buildVector),
("vector-length", vectorLength),
("vector-ref", vectorRef),
("vector->list", vectorToList),
("list->vector", listToVector),
("make-hash-table", hashTblMake),
("hash-table?", isHashTbl),
-- TODO: alist->hash-table
("hash-table-exists?", hashTblExists),
("hash-table-ref", hashTblRef),
("hash-table-size", hashTblSize),
("hash-table->alist", hashTbl2List),
("hash-table-keys", hashTblKeys),
("hash-table-values", hashTblValues),
-- TODO next: hash-table-walk, hash-table-fold
-- TODO: many more, see SRFI
("hash-table-copy", hashTblCopy),
("string?", isString),
("string", buildString),
("make-string", makeString),
("string-length", stringLength),
("string-ref", stringRef),
("substring", substring),
("string-append", stringAppend),
("string->number", stringToNumber),
("string->list", stringToList),
("list->string", listToString),
("string-copy", stringCopy),
("boolean?", isBoolean)]
data Unpacker = forall a. Eq a => AnyUnpacker (LispVal -> ThrowsError a)
unpackEquals :: LispVal -> LispVal -> Unpacker -> ThrowsError Bool
unpackEquals arg1 arg2 (AnyUnpacker unpacker) =
do unpacked1 <- unpacker arg1
unpacked2 <- unpacker arg2
return $ unpacked1 == unpacked2
`catchError` (const $ return False)
boolBinop :: (LispVal -> ThrowsError a) -> (a -> a -> Bool) -> [LispVal] -> ThrowsError LispVal
boolBinop unpacker op args = if length args /= 2
then throwError $ NumArgs 2 args
else do left <- unpacker $ args !! 0
right <- unpacker $ args !! 1
return $ Bool $ left `op` right
unaryOp :: (LispVal -> ThrowsError LispVal) -> [LispVal] -> ThrowsError LispVal
unaryOp f [v] = f v
unaryOp _ [] = throwError $ NumArgs 1 []
unaryOp _ args@(_ : _) = throwError $ NumArgs 1 args
--numBoolBinop :: (Integer -> Integer -> Bool) -> [LispVal] -> ThrowsError LispVal
--numBoolBinop = boolBinop unpackNum
strBoolBinop :: (String -> String -> Bool) -> [LispVal] -> ThrowsError LispVal
strBoolBinop = boolBinop unpackStr
boolBoolBinop :: (Bool -> Bool -> Bool) -> [LispVal] -> ThrowsError LispVal
boolBoolBinop = boolBinop unpackBool
unpackStr :: LispVal -> ThrowsError String
unpackStr (String s) = return s
unpackStr (Number s) = return $ show s
unpackStr (Bool s) = return $ show s
unpackStr notString = throwError $ TypeMismatch "string" notString
unpackBool :: LispVal -> ThrowsError Bool
unpackBool (Bool b) = return b
unpackBool notBool = throwError $ TypeMismatch "boolean" notBool
{- List primitives -}
car :: [LispVal] -> ThrowsError LispVal
car [List (x : _)] = return x
car [DottedList (x : _) _] = return x
car [badArg] = throwError $ TypeMismatch "pair" badArg
car badArgList = throwError $ NumArgs 1 badArgList
cdr :: [LispVal] -> ThrowsError LispVal
cdr [List (_ : xs)] = return $ List xs
cdr [DottedList [_] x] = return x
cdr [DottedList (_ : xs) x] = return $ DottedList xs x
cdr [badArg] = throwError $ TypeMismatch "pair" badArg
cdr badArgList = throwError $ NumArgs 1 badArgList
cons :: [LispVal] -> ThrowsError LispVal
cons [x1, List []] = return $ List [x1]
cons [x, List xs] = return $ List $ x : xs
cons [x, DottedList xs xlast] = return $ DottedList (x : xs) xlast
cons [x1, x2] = return $ DottedList [x1] x2
cons badArgList = throwError $ NumArgs 2 badArgList
equal :: [LispVal] -> ThrowsError LispVal
equal [(Vector arg1), (Vector arg2)] = eqvList equal [List $ (elems arg1), List $ (elems arg2)]
-- TODO: hash table?
equal [l1@(List _), l2@(List _)] = eqvList equal [l1, l2]
equal [(DottedList xs x), (DottedList ys y)] = equal [List $ xs ++ [x], List $ ys ++ [y]]
equal [arg1, arg2] = do
primitiveEquals <- liftM or $ mapM (unpackEquals arg1 arg2)
[AnyUnpacker unpackNum, AnyUnpacker unpackStr, AnyUnpacker unpackBool]
eqvEquals <- eqv [arg1, arg2]
return $ Bool $ (primitiveEquals || let (Bool x) = eqvEquals in x)
equal badArgList = throwError $ NumArgs 2 badArgList
-------------- Vector Primitives --------------
makeVector, buildVector, vectorLength, vectorRef, vectorToList, listToVector :: [LispVal] -> ThrowsError LispVal
makeVector [(Number n)] = makeVector [Number n, List []]
makeVector [(Number n), a] = do
let l = replicate (fromInteger n) a
return $ Vector $ (listArray (0, length l - 1)) l
makeVector [badType] = throwError $ TypeMismatch "integer" badType
makeVector badArgList = throwError $ NumArgs 1 badArgList
buildVector (o:os) = do
let lst = o:os
return $ Vector $ (listArray (0, length lst - 1)) lst
buildVector badArgList = throwError $ NumArgs 1 badArgList
vectorLength [(Vector v)] = return $ Number $ toInteger $ length (elems v)
vectorLength [badType] = throwError $ TypeMismatch "vector" badType
vectorLength badArgList = throwError $ NumArgs 1 badArgList
vectorRef [(Vector v), (Number n)] = return $ v ! (fromInteger n)
vectorRef [badType] = throwError $ TypeMismatch "vector integer" badType
vectorRef badArgList = throwError $ NumArgs 2 badArgList
vectorToList [(Vector v)] = return $ List $ elems v
vectorToList [badType] = throwError $ TypeMismatch "vector" badType
vectorToList badArgList = throwError $ NumArgs 1 badArgList
listToVector [(List l)] = return $ Vector $ (listArray (0, length l - 1)) l
listToVector [badType] = throwError $ TypeMismatch "list" badType
listToVector badArgList = throwError $ NumArgs 1 badArgList
-------------- Hash Table Primitives --------------
-- Future: support (equal?), (hash) parameters
hashTblMake, isHashTbl, hashTblExists, hashTblRef, hashTblSize, hashTbl2List, hashTblKeys, hashTblValues, hashTblCopy:: [LispVal] -> ThrowsError LispVal
hashTblMake _ = return $ HashTable $ Data.Map.fromList []
isHashTbl [(HashTable _)] = return $ Bool True
isHashTbl _ = return $ Bool False
hashTblExists [(HashTable ht), key@(_)] = do
case Data.Map.lookup key ht of
Just _ -> return $ Bool True
Nothing -> return $ Bool False
hashTblExists [] = throwError $ NumArgs 2 []
hashTblExists args@(_ : _) = throwError $ NumArgs 2 args
hashTblRef [(HashTable ht), key@(_)] = do
case Data.Map.lookup key ht of
Just val -> return $ val
Nothing -> throwError $ BadSpecialForm "Hash table does not contain key" key
hashTblRef [(HashTable ht), key@(_), Func _ _ _ _] = do
case Data.Map.lookup key ht of
Just val -> return $ val
Nothing -> throwError $ NotImplemented "thunk"
-- FUTURE: a thunk can optionally be specified, this drives definition of /default
-- Nothing -> apply thunk []
hashTblRef [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblRef badArgList = throwError $ NumArgs 2 badArgList
hashTblSize [(HashTable ht)] = return $ Number $ toInteger $ Data.Map.size ht
hashTblSize [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblSize badArgList = throwError $ NumArgs 1 badArgList
hashTbl2List [(HashTable ht)] = do
return $ List $ map (\(k, v) -> List [k, v]) $ Data.Map.toList ht
hashTbl2List [badType] = throwError $ TypeMismatch "hash-table" badType
hashTbl2List badArgList = throwError $ NumArgs 1 badArgList
hashTblKeys [(HashTable ht)] = do
return $ List $ map (\(k, _) -> k) $ Data.Map.toList ht
hashTblKeys [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblKeys badArgList = throwError $ NumArgs 1 badArgList
hashTblValues [(HashTable ht)] = do
return $ List $ map (\(_, v) -> v) $ Data.Map.toList ht
hashTblValues [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblValues badArgList = throwError $ NumArgs 1 badArgList
hashTblCopy [(HashTable ht)] = do
return $ HashTable $ Data.Map.fromList $ Data.Map.toList ht
hashTblCopy [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblCopy badArgList = throwError $ NumArgs 1 badArgList
-------------- String Primitives --------------
buildString :: [LispVal] -> ThrowsError LispVal
buildString [(Char c)] = return $ String [c]
buildString (Char c:rest) = do
cs <- buildString rest
case cs of
String s -> return $ String $ [c] ++ s
badType -> throwError $ TypeMismatch "character" badType
buildString [badType] = throwError $ TypeMismatch "character" badType
buildString badArgList = throwError $ NumArgs 1 badArgList
makeString :: [LispVal] -> ThrowsError LispVal
makeString [(Number n)] = return $ doMakeString n ' ' ""
makeString [(Number n), (Char c)] = return $ doMakeString n c ""
makeString badArgList = throwError $ NumArgs 1 badArgList
doMakeString :: forall a.(Num a) => a -> Char -> String -> LispVal
doMakeString n char s =
if n == 0
then String s
else doMakeString (n - 1) char (s ++ [char])
stringLength :: [LispVal] -> ThrowsError LispVal
stringLength [String s] = return $ Number $ foldr (const (+1)) 0 s -- Could probably do 'length s' instead...
stringLength [badType] = throwError $ TypeMismatch "string" badType
stringLength badArgList = throwError $ NumArgs 1 badArgList
stringRef :: [LispVal] -> ThrowsError LispVal
stringRef [(String s), (Number k)] = return $ Char $ s !! fromInteger k
stringRef [badType] = throwError $ TypeMismatch "string number" badType
stringRef badArgList = throwError $ NumArgs 2 badArgList
substring :: [LispVal] -> ThrowsError LispVal
substring [(String s), (Number start), (Number end)] =
do let slength = fromInteger $ end - start
let begin = fromInteger start
return $ String $ (take slength . drop begin) s
substring [badType] = throwError $ TypeMismatch "string number number" badType
substring badArgList = throwError $ NumArgs 3 badArgList
stringCIEquals :: [LispVal] -> ThrowsError LispVal
stringCIEquals [(String str1), (String str2)] = do
if (length str1) /= (length str2)
then return $ Bool False
else return $ Bool $ ciCmp str1 str2 0
where ciCmp s1 s2 idx = if idx == (length s1)
then True
else if (toLower $ s1 !! idx) == (toLower $ s2 !! idx)
then ciCmp s1 s2 (idx + 1)
else False
stringCIEquals [badType] = throwError $ TypeMismatch "string string" badType
stringCIEquals badArgList = throwError $ NumArgs 2 badArgList
stringCIBoolBinop :: ([Char] -> [Char] -> Bool) -> [LispVal] -> ThrowsError LispVal
stringCIBoolBinop op [(String s1), (String s2)] = boolBinop unpackStr op [(String $ strToLower s1), (String $ strToLower s2)]
where strToLower str = map (toLower) str
stringCIBoolBinop _ [badType] = throwError $ TypeMismatch "string string" badType
stringCIBoolBinop _ badArgList = throwError $ NumArgs 2 badArgList
stringAppend :: [LispVal] -> ThrowsError LispVal
stringAppend [(String s)] = return $ String s -- Needed for "last" string value
stringAppend (String st:sts) = do
rest <- stringAppend sts
-- TODO: I needed to use <- instead of "let = " here, for type problems. Why???
-- TBD: this probably will solve type problems when processing other lists of objects in the other string functions
case rest of
String s -> return $ String $ st ++ s
other -> throwError $ TypeMismatch "string" other
stringAppend [badType] = throwError $ TypeMismatch "string" badType
stringAppend badArgList = throwError $ NumArgs 1 badArgList
-- This could be expanded, for now just converts integers
-- TODO: handle a radix param
stringToNumber :: [LispVal] -> ThrowsError LispVal
stringToNumber [(String s)] = do
result <- (readExpr s) -- result <- parseExpr s
case result of
n@(Number _) -> return n
n@(Rational _) -> return n
n@(Float _) -> return n
n@(Complex _) -> return n
_ -> return $ Bool False
stringToNumber [badType] = throwError $ TypeMismatch "string" badType
stringToNumber badArgList = throwError $ NumArgs 1 badArgList
stringToList :: [LispVal] -> ThrowsError LispVal
stringToList [(String s)] = return $ List $ map (Char) s
stringToList [badType] = throwError $ TypeMismatch "string" badType
stringToList badArgList = throwError $ NumArgs 1 badArgList
listToString :: [LispVal] -> ThrowsError LispVal
listToString [(List [])] = return $ String ""
listToString [(List l)] = buildString l
listToString [badType] = throwError $ TypeMismatch "list" badType
listToString [] = throwError $ NumArgs 1 []
listToString args@(_ : _) = throwError $ NumArgs 1 args
stringCopy :: [LispVal] -> ThrowsError LispVal
stringCopy [String s] = return $ String s
stringCopy [badType] = throwError $ TypeMismatch "string" badType
stringCopy badArgList = throwError $ NumArgs 2 badArgList
isDottedList :: [LispVal] -> ThrowsError LispVal
isDottedList ([DottedList _ _]) = return $ Bool True
-- Must include lists as well since they are made up of 'chains' of pairs
isDottedList ([List []]) = return $ Bool False
isDottedList ([List _]) = return $ Bool True
isDottedList _ = return $ Bool False
isProcedure :: [LispVal] -> ThrowsError LispVal
isProcedure ([Continuation _ _ _ _ _]) = return $ Bool True
isProcedure ([PrimitiveFunc _]) = return $ Bool True
isProcedure ([Func _ _ _ _]) = return $ Bool True
isProcedure ([IOFunc _]) = return $ Bool True
isProcedure _ = return $ Bool False
isVector, isList :: LispVal -> ThrowsError LispVal
isVector (Vector _) = return $ Bool True
isVector _ = return $ Bool False
isList (List _) = return $ Bool True
isList _ = return $ Bool False
isNull :: [LispVal] -> ThrowsError LispVal
isNull ([List []]) = return $ Bool True
isNull _ = return $ Bool False
isSymbol :: [LispVal] -> ThrowsError LispVal
isSymbol ([Atom _]) = return $ Bool True
isSymbol _ = return $ Bool False
symbol2String :: [LispVal] -> ThrowsError LispVal
symbol2String ([Atom a]) = return $ String a
symbol2String [notAtom] = throwError $ TypeMismatch "symbol" notAtom
symbol2String [] = throwError $ NumArgs 1 []
symbol2String args@(_ : _) = throwError $ NumArgs 1 args
string2Symbol :: [LispVal] -> ThrowsError LispVal
string2Symbol ([String s]) = return $ Atom s
string2Symbol [] = throwError $ NumArgs 1 []
string2Symbol [notString] = throwError $ TypeMismatch "string" notString
string2Symbol args@(_ : _) = throwError $ NumArgs 1 args
isChar :: [LispVal] -> ThrowsError LispVal
isChar ([Char _]) = return $ Bool True
isChar _ = return $ Bool False
isString :: [LispVal] -> ThrowsError LispVal
isString ([String _]) = return $ Bool True
isString _ = return $ Bool False
isBoolean :: [LispVal] -> ThrowsError LispVal
isBoolean ([Bool _]) = return $ Bool True
isBoolean _ = return $ Bool False
-- end Eval section
{- Should not need this function, since we are using Haskell
trampoline :: Env -> LispVal -> IOThrowsError LispVal
trampoline env val = do
result <- eval env val
case result of
-- If a form is not fully-evaluated to a value, bounce it back onto the trampoline...
func@(Func params vararg body closure True) -> trampoline env func -- next iteration, via tail call (?)
val -> return val
-}
{- My original notes about implementing continuations
-
- TODO: write a wiki page about continuations once everything is implemented.
- maybe use some of this as background material for the article.
-
- Changes will be required to eval to support continuations. According to original wiki book:
- TBD
-
-
- Need to rethink below and come up with a clear, top-level design approach. Some starting points
- for this are:
- http://c2.com/cgi/wiki?ContinuationImplementation
- http://c2.com/cgi/wiki?CallWithCurrentContinuation (the link to this book may be helpful as well: http://c2.com/cgi/wiki?EssentialsOfProgrammingLanguages - apparently if the interpreter is written using CPS, then call/cc is free)
- http://tech.phillipwright.com/2010/05/23/continuations-in-scheme/
- http://community.schemewiki.org/?call-with-current-continuation
-
- ALSO, consider the following quote:
- "CPS is a programming style where no function is ever allowed to return."
- So, this would mean that when evaluating a simple integer, string, etc eval should call into
- the continuation instead of just returning.
- Need to think about how this will be handled, how functions will be called using CPS, and what
- the continuation data type needs to contain.
-
-
-
-
-
- Some of my notes:
- as simple as using CPS to evaluate lists of "lines" (body)? Then could pass the next part of the CPS as the cont arg to eval. Or is this too simple to work? need to think about this - http://en.wikipedia.org/wiki/Continuation-passing_style
-
- Possible design approach:
-
- * thread cont through eval
- * instead of returning, call into next eval using CPS style, with the cont parameter.
- this replaces code in evalBody (possibly other places?) that uses local CPS to execute a function
- * parameter will consist of a lisp function
- * eval will call into another function to deal with details of manipulating the cont prior to next call
- need to work out details of exactly how that would work, but could for example just go to the next line
- of body.
- * To continue above point, where is eval'd value returned to? May want to refer to R5RS section that describes call/cc:
- A common use of call-with-current-continuation is for structured, non-local exits from loops or procedure bodies, but in fact call-with-current-continuation is extremely useful for implementing a wide variety of advanced control structures.
-
- Whenever a Scheme expression is evaluated there is a continuation wanting the result of the expression. The continuation represents an entire (default) future for the computation. If the expression is evaluated at top level, for example, then the continuation might take the result, print it on the screen, prompt for the next input, evaluate it, and so on forever. Most of the time the continuation includes actions specified by user code, as in a continuation that will take the result, multiply it by the value stored in a local variable, add seven, and give the answer to the top level continuation to be printed. Normally these ubiquitous continuations are hidden behind the scenes and programmers do not think much about them. On rare occasions, however, a programmer may need to deal with continuations explicitly. Call-with-current-continuation allows Scheme programmers to do that by creating a procedure that acts just like the current continuation.
-
- Most programming languages incorporate one or more special-purpose escape constructs with names like exit, return, or even goto. In 1965, however, Peter Landin [16] invented a general purpose escape operator called the J-operator. John Reynolds [24] described a simpler but equally powerful construct in 1972. The catch special form described by Sussman and Steele in the 1975 report on Scheme is exactly the same as Reynolds's construct, though its name came from a less general construct in MacLisp. Several Scheme implementors noticed that the full power of the catch construct could be provided by a procedure instead of by a special syntactic construct, and the name call-with-current-continuation was coined in 1982. This name is descriptive, but opinions differ on the merits of such a long name, and some people use the name call/cc instead.
-
- * need to consider what would be passed when evaluating via a REPL, at top-level, via haskell entry points, etc...
-
- -}