------------------------------------------------------------------------------ --- A simple interpreter for ICurry based on the a small-step semantics. --- --- The following invariants are required for ICurry programs: --- 1. No nested case expression --- 2. If there is a case expression, it is on some argument and the --- argument index is contained in the demand information of the function. --- --- @author Michael Hanus, Sascha Ecks --- @version October 2022 ------------------------------------------------------------------------------ module ICurry.Interpreter where import Control.Monad ( when, unless ) import Data.List ( init, isPrefixOf, last, replace ) import System.Process ( sleep, system ) import ICurry.Types import ICurry.Graph import ICurry.Compiler ( icCompile ) import ICurry.Options ( ICOptions(..), defaultICOptions ) import qualified TermGraph.XML as TG ------------------------------------------------------------------------------ -- The options of the ICurry interpreter. data IOptions = IOptions { icOptions :: ICOptions -- inherit options of the ICurry compiler , showAllExps :: Bool -- show all expressions represented by the graph , waitTime :: Int -- seconds to wait in non-interactive mode , stepNum :: Int -- step number (internal) } -- Default options: quiet non-interactive mode defOpts :: IOptions defOpts = IOptions defaultICOptions False 0 0 withGraph :: IOptions -> Int withGraph opts = optShowGraph (icOptions opts) ------------------------------------------------------------------------------ -- The finger print is a partial mapping from choice identifiers to integers. type FingerPrint = [(ChoiceID,Int)] data Control = CNode NodeID | IBlockEnv IBlock IEnv deriving Show -- An environment is a mapping from IVars to node identifiers. type IEnv = [(IVarIndex, NodeID)] lookupInEnv :: IVarIndex -> IEnv -> NodeID lookupInEnv v env = maybe (error "Variable not found in environment") id (lookup v env) updateEnv :: IEnv -> IVarIndex -> NodeID -> IEnv updateEnv [] v n = [(v,n)] updateEnv ((v',m) : env) v n = if v==v' then (v,n) : env else (v',m) : updateEnv env v n -- A task of the execution contains the control, -- a stack of function nodes together with the index of the demanded argument, -- and a finger print. data Task = Task Control [(NodeID,Int)] FingerPrint deriving Show -- Returns the root node of the expression to be evaluated by a task. rootOfTask :: Task -> NodeID rootOfTask (Task ctrl stk _) | null stk = case ctrl of CNode nid -> nid IBlockEnv _ env -> lookupInEnv 0 env | otherwise = fst (last stk) -- Returns the node currently evaluated. currentNodeOfTask :: Task -> NodeID currentNodeOfTask (Task (CNode nid) _ _) = nid currentNodeOfTask (Task (IBlockEnv _ env) _ _) = lookupInEnv 0 env ------------------------------------------------------------------------------ -- The state of an ICurry program under evaluation as described in the -- WFLP'19 paper. -- The auxiliary component `currResult` is set in a step when a new result -- has been computed. data State = State { program :: [IFunction] , graph :: Graph , tasks :: [Task] , results :: [NodeID] , currResult :: Maybe NodeID } deriving Show -- Initial state for a program, graph, and root node id. initState :: [IFunction] -> Graph -> NodeID -> State initState prog graph nid = State prog graph [Task (CNode nid) [] []] [] Nothing -- Returns the root nodes of all results and all expressions. rootsOfState :: State -> [NodeID] rootsOfState st = results st ++ map rootOfTask (tasks st) -- Show all results stored in a state. showResults :: State -> String showResults st = unlines (map (showGraphExp (graph st)) (results st)) -- Adds a result to a program state. addResult :: NodeID -> State -> State addResult nid st = st { results = results st ++ [nid], currResult = Just nid } addTGState :: ICOptions -> State -> [TG.State] -> [TG.State] addTGState icopts st states | optTermGraph icopts = case (tasks st) of -- also return state when only IReturn is currently in Tasks IBlock? -- or always return state and only append it in runWith if it changed tsk : _ -> if (not (null states)) && ((nstate) == (last states)) then states else states ++ [nstate] where nstate = TG.State rgraph (currentNodeOfTask tsk) (results st) (fp tsk) [] -> states ++ [ TG.State rgraph 0 (results st) [] ] | otherwise = states where rgraph = reachableGraph (graph st) [graphRoot (graph st)] fp (Task _ _ fingerprint) = fingerprint -- Print the current state of the interpreter according to the given options. printState :: IOptions -> State -> IO () printState opts st = do when (verb > 2) $ putStr $ unlines [ "RAW GRAPH : " ++ show (graph st) , "TASKS : " ++ show tsks ] when (showAllExps opts) $ putStr $ unlines $ "ALL EXPRESSIONS:" : map (showGraphExp (graph st)) (rootsOfState st) when (verb == 1) $ case tsks of [] -> putStrLn "NO TASK" tsk:_ -> putStr $ unlines $ [ "CURRENT EXPR: " ++ showGraphExp (graph st) (rootOfTask tsk) ] when (verb > 1) $ case tsks of [] -> putStrLn "NO TASK" tsk@(Task ctrl _ fp) : _ -> putStr $ unlines $ [ "CURRENT TASK:" , "MAIN EXPR : " ++ showGraphExp (graph st) (rootOfTask tsk) ] ++ if verb > 2 then [ "CONTROL : " ++ showControl ctrl , "FINGER PRINT: " ++ show fp ] else [] when (withGraph opts > 0 || not (null (optOutput (icOptions opts)))) $ showStateGraph when (waitTime opts > 0 && not (optInteractive (icOptions opts))) $ sleep (waitTime opts) when (verb > 1) $ putStrLn "" where verb = optVerb (icOptions opts) tsks = tasks st showControl (CNode nid) = "NODE: " ++ show nid showControl (IBlockEnv b e) = "BLOCK: " ++ show b ++ "\n ENV: " ++ show e -- Visualize the graph contained in the current state as a dot graph. showStateGraph = do let ndcolors = (if null tsks then id else markCurrent (currentNodeOfTask (head tsks))) (map (\ (i,t) -> (rootOfTask t, [("color",if i==1 then "red" else "blue")])) (zip [1..] tsks)) ++ map (\n -> (n,[("color","green"),("style","filled")])) (results st) viewDot Nothing (stepNum opts) (graphToDot (graph st) ndcolors (withGraph opts > 2) (withGraph opts > 1)) where markCurrent cn [] = [(cn, yellowFill)] markCurrent cn ((nid,nas) : ncs) | nid == cn = (nid, nas ++ yellowFill) : ncs | otherwise = (nid, nas): markCurrent cn ncs yellowFill = [("fillcolor","yellow"),("style","filled")] {- The following coloring is used in the graph: - red node: root of the active task - blue node: root of an inactive task - green node: root of a computed result - yellow filled node: root of the current contol -} askProceed :: IOptions -> IO Bool askProceed opts = if optInteractive (icOptions opts) then do putStr "Proceed () or abort (a)? " ans <- getLine if null ans then return True else if ans `isPrefixOf` "abort" then putStrLn "Execution aborted!" >> return False else askProceed opts else return True ------------------------------------------------------------------------------ -- An interpreter for a single Curry program based on translating -- them into ICurry. -- The program name and the unqualified name of the main function -- must be provided as string arguments. -- It also prints intermediate steps, PDFs, etc. accordding to the options. execProg :: IOptions -> String -> String -> IO ([TG.State]) execProg opts progname fname = do iprog <- icCompile defaultICOptions progname execIProg opts iprog fname -- An interpreter for ICurry programs. -- Executes a program with a main function where the name is provided -- as a string. -- It also prints intermediate steps, PDFs, etc. accordding to the options. execIProg :: IOptions -> IProg -> String -> IO ([TG.State]) execIProg opts (IProg _ _ _ ifuns) f = do let (g,ni) = addNode (FuncNode f []) emptyGraph pdfmain = optOutput (icOptions opts) opts1 = if null pdfmain then opts else opts { icOptions = (icOptions opts) { optShowGraph = 0 } , stepNum = 1 } when (withGraph opts1 > 0) $ viewDot (Just $ optViewPDF (icOptions opts)) 0 (graphToDot g [] (withGraph opts1 > 2) (withGraph opts1 > 1)) let allfuns = ifuns ++ standardFuncs unless (arityOf f allfuns == 0) $ error $ "Main function '" ++ f ++ "' has non-zero arity!" (opts2,states) <- runWith opts1 (initState allfuns g ni) [] unless (null pdfmain) $ do -- Concatenate all step PDFs into on PDF: let pdffiles = map (\i -> "ICURRYDOT" ++ show i ++ ".pdf") [1 .. stepNum opts2] system $ unwords $ "pdftk" : pdffiles ++ ["cat", "output", pdfmain] system $ unwords $ "/bin/rm -f" : pdffiles putStrLn $ "PDFs of all steps written to '" ++ pdfmain ++ "'." return states where checkMainFunc ifs f = do let IFunction _ ar _ _ _ = funcOf f ifs unless (ar == 0) $ error $ "Function '" ++ f ++ "' has non-zero arity!" runWith :: IOptions -> State -> [TG.State] -> IO (IOptions, [TG.State]) runWith opts st states | optMaxSteps (icOptions opts) == length states = do printState opts st return (opts, states) | null (tasks st) = do printState opts st let nstates = addTGState (icOptions opts) st states return (opts, nstates) | otherwise = do printState opts st let nstates = addTGState (icOptions opts) st states procstep <- if optVerb (icOptions opts) > 0 then askProceed opts else return True if not procstep then return (opts, nstates) else do let num = stepNum opts nopts = if num==0 then opts else opts { stepNum = num + 1 } nst = step st maybe (runWith nopts nst nstates) (\nid -> do putStrLn $ "RESULT: " ++ showGraphExp (graph nst) nid proceed <- askProceed opts if proceed then runWith nopts (nst {currResult = Nothing}) nstates else return (opts, nstates)) (currResult nst) -- Evaluates a 0-ary function w.r.t. an ICurry program and returns -- the list of all results formatted as strings. -- Used for testing. evalFun :: IProg -> String -> [String] evalFun (IProg _ _ _ ifuns) f = let (g,ni) = addNode (FuncNode f []) emptyGraph in evaluate (initState ifuns g ni) where evaluate st | null (tasks st) = [] | otherwise = let st' = step st in maybe (evaluate st') (\nid -> showGraphExp (graph st') nid : evaluate st' {currResult = Nothing}) (currResult st') ------------------------------------------------------------------------------ -- Implementation of the small-step semantics. -- The small step. step :: State -> State step st = evalFirstTask st (tasks st) -- The small step on the first task. evalFirstTask :: State -> [Task] -> State evalFirstTask _ [] = error "step: empty tasks" evalFirstTask st (Task (CNode nid) stk fp : tsks) = case lookupNode nid (graph st) of ConsNode _ _ -> case stk of [] -> addResult nid (st { tasks = tsks }) ((fnid,_) : rstk) -> let st1 = st { tasks = Task (CNode fnid) rstk fp : tsks } in invokeFunction st1 (tasks st1) -- partial calls are treated as constructors: PartNode _ _ _ -> case stk of [] -> addResult nid (st { tasks = tsks }) ((fnid,_) : rstk) -> let st1 = st { tasks = Task (CNode fnid) rstk fp : tsks } in invokeFunction st1 (tasks st1) FuncNode f _ -> case demandOf f (program st) of Nothing -> invokeFunction st (tasks st) Just di -> let ni = followPath (graph st) nid [di] in st { tasks = Task (CNode ni) ((nid,di) : stk) fp : tsks } ChoiceNode cid n1 n2 -> case stk of [] -> case lookup cid fp of Just c -> let ns = if c==1 then n1 else n2 in st { tasks = Task (CNode ns) stk fp : tsks } Nothing -> let newtasks = [Task (CNode n1) [] ((cid,1) : fp), Task (CNode n2) [] ((cid,2) : fp)] in st { tasks = tsks ++ newtasks } ((fnid,di) : nids) -> -- pull-tab step: let g0 = graph st in case lookupNode fnid g0 of FuncNode f ns -> let (g1,n1') = addNode (FuncNode f (replace n1 di ns)) g0 (g2,n2') = addNode (FuncNode f (replace n2 di ns)) g1 in st { graph = updateNode g2 fnid (ChoiceNode cid n1' n2') , tasks = Task (CNode fnid) nids fp : tsks } _ -> error "step: stack does not refer to function node" FreeNode -> case stk of [] -> addResult nid (st { tasks = tsks }) ((fnid,_) : rstk) -> -- bind free node to choice structure corresponding to case expression maybe (let newtsks = Task (CNode fnid) rstk fp : tsks in invokeFunction (st { tasks = newtsks }) newtsks) (\chexp -> let (gr1,nd) = extendGraph (graph st) [] chexp chnd = either (error "evalFirstTask: no choice") id nd in st { graph = updateNode gr1 nid chnd }) (choiceOfDemand st fnid) evalFirstTask st (Task (IBlockEnv (IBlock vs asgns stm) ienv) stk fp : tsks) = let (g0,ienv0) = addVarDecls (graph st) ienv vs (g1,ienv1) = addAssigns g0 ienv0 asgns in case stm of IExempt -> st { tasks = tsks } -- failure: remove current task IReturn iexp -> -- return statement: replace current ROOT node let (g2,nexp) = extendGraph g1 ienv1 iexp rootid = lookupInEnv 0 ienv in either (\ni -> st { graph = replaceNode g2 rootid ni, tasks = Task (CNode ni) stk fp : tsks }) (\nd -> st { graph = updateNode g2 rootid nd, tasks = Task (CNode rootid) stk fp : tsks }) nexp ICaseCons cv branches -> -- constructor case: select branch let bn = lookupInEnv cv ienv1 sb = selectConsBranch (lookupNode bn g1) branches in st { graph = g1 , tasks = Task (IBlockEnv sb ienv1) stk fp : tsks } ICaseLit cv branches -> -- literal case: select branch let bn = lookupInEnv cv ienv1 sb = selectLitBranch (lookupNode bn g1) branches in st { graph = g1 , tasks = Task (IBlockEnv sb ienv1) stk fp : tsks } -- This operation is used when the control of the first task contains -- a function node ready for execution, i.e., a possibly demanded argument -- has been evaluated. -- Then the control is replaced by the body of the function -- (or by the result of executing some external operation). invokeFunction :: State -> [Task] -> State invokeFunction _ [] = error "invokeFunction: empty tasks" invokeFunction st (Task (CNode nid) stk fp : tsks) = case lookupNode nid gr of FuncNode f ns -> case bodyOf f (program st) of IFuncBody blck -> let ienv = [(0, nid)] in st { tasks = Task (IBlockEnv blck ienv) stk fp : tsks } IExternal en -> case en of "normalForm" -> let nfarg = ns !! 0 in case lookupNode nfarg gr of ConsNode c cargs -> let argsenv = zip [1..] cargs evalcargs = foldl (\xs x -> IFCall ("","$$!",0) [xs, IFCall ("","normalForm",0) [IVar (fst x)]]) (ICPCall ("",c,0) (length cargs) []) argsenv (gr1,nexp) = extendGraph gr argsenv evalcargs in st { graph = either (error "Internal error in normalForm") (updateNode gr1 nid) nexp } FreeNode -> -- Warning: this does not work of free variable will be -- later instantiated! st { graph = replaceNode gr nid nfarg , tasks = Task (CNode nfarg) stk fp : tsks } _ -> error "step: use of 'normalForm' without constructor argument" _ -> st { graph = updateNode gr nid (evalExternal gr en ns) } _ -> error "invokeFunction: no function node in control" where gr = graph st invokeFunction _ (Task (IBlockEnv _ _) _ _ : _) = error "invokeFunction: no function node in control" -- Evaluates an external function to a node containing the evaluated value. -- The arguments are the current graph, the external name, -- and the argument nodes. evalExternal :: Graph -> String -> [NodeID] -> Node evalExternal gr ename ns = case unQName ename of "apply" -> addPartialArg (lookupNode (ns!!0) gr) (ns!!1) "$!" -> FuncNode "apply" ns "$#" -> FuncNode "apply" ns "prim_Int_plus" -> ConsNode (show (lookupIntNode (ns!!0) gr + lookupIntNode (ns!!1) gr)) [] "prim_Int_mult" -> ConsNode (show (lookupIntNode (ns!!0) gr * lookupIntNode (ns!!1) gr)) [] _ -> error $ "step: unknown external function: " ++ ename where unQName s = let (mn,ufn) = break (=='.') s in if null ufn then mn else unQName (tail ufn) lookupIntNode :: NodeID -> Graph -> Int lookupIntNode nid gr = case lookupNode nid gr of ConsNode c [] -> read c :: Int _ -> error "lookupIntNode: no integer found" -- Selects the constructor branch corresponding to some constructor node. selectConsBranch :: Node -> [IConsBranch] -> IBlock selectConsBranch nd [] = error $ "selectConsBranch: no branch for node: " ++ show nd selectConsBranch nd (IConsBranch (_,c,_) _ blck : branches) = case nd of ConsNode nc _ -> if nc == c then blck else selectConsBranch nd branches _ -> error $ "selectConsBranch: unevaluated branch node: " ++ show nd -- Selects the literal branch corresponding to some literal node. selectLitBranch :: Node -> [ILitBranch] -> IBlock selectLitBranch nd [] = error $ "selectLitBranch: no branch for node: " ++ show nd selectLitBranch nd (ILitBranch l blck : branches) = case nd of ConsNode nc _ -> if nc == showILit l then blck else selectLitBranch nd branches _ -> error $ "selectLitBranch: unevaluated branch node: " ++ show nd -- Adds variable declarations to the graph and environment. addVarDecls :: Graph -> IEnv -> [IVarDecl] -> (Graph,IEnv) addVarDecls g env [] = (g,env) addVarDecls g env (IVarDecl v : vdecls) = addVarDecls g ((v,0) : env) vdecls addVarDecls g env (IFreeDecl v : vdecls) = let (g1,fn) = addNode FreeNode g in addVarDecls g1 ((v,fn) : env) vdecls -- Adds assignments to the graph and environment. addAssigns :: Graph -> IEnv -> [IAssign] -> (Graph,IEnv) addAssigns g env [] = (g,env) addAssigns g env (IVarAssign v e : asgns) = let (g1,ne) = extendGraph g env e (g2,nid) = either (\ni -> (g1,ni)) (\nd -> addNode nd g1) ne in addAssigns g2 (updateEnv env v nid) asgns addAssigns _ _ (INodeAssign _ [] _ : _) = error "addAssigns: empty path" addAssigns g env (INodeAssign v path@(_:_) e : asgns) = let n = followPath g (lookupInEnv v env) (init path) (g1,ne) = extendGraph g env e (g2,nid) = either (\ni -> (g1,ni)) (\nd -> addNode nd g1) ne in addAssigns (replaceNodeArg g2 n (last path) nid) env asgns -- Replaces the i-th successor of node `nid` by node `narg`. replaceNodeArg :: Graph -> NodeID -> Int -> NodeID -> Graph replaceNodeArg g nid i narg = case lookupNode nid g of ConsNode c ns -> updateNode g nid (ConsNode c (replace narg i ns)) FuncNode f ns -> updateNode g nid (FuncNode f (replace narg i ns)) PartNode f m ns -> updateNode g nid (PartNode f m (replace narg i ns)) ChoiceNode _ _ _ -> error "replaceNodeArg: ChoiceNode" FreeNode -> error "replaceNodeArg: FreeNode" -- Follows a path from a given node. followPath :: Graph -> NodeID -> [Int] -> NodeID followPath _ n [] = n followPath g n (i:is) = case lookupNode n g of ConsNode _ ns -> followPath g (selectArg ns) is FuncNode _ ns -> followPath g (selectArg ns) is PartNode _ _ ns -> followPath g (selectArg ns) is ChoiceNode _ n1 n2 -> followPath g (selectArg [n1,n2]) is FreeNode -> error "followPath: FreeNode" where selectArg ns | i >= length ns = error "followPath: argument does not exist!" | otherwise = ns !! i -- Extends a graph w.r.t. a given environment and ICurry expression -- so that a expression is represented in the graph. -- The result is either a node identifier of an existing node (if the -- expression already exists in graph) or the contents of a new node -- to be added. -- Used for assignments and return statements (ISimpleBlock). extendGraph :: Graph -> IEnv -> IExpr -> (Graph, Either NodeID Node) extendGraph g0 env (IVar v) = (g0, Left $ lookupInEnv v env) extendGraph g0 env (IVarAccess v path) = (g0, Left $ followPath g0 (lookupInEnv v env) path) extendGraph g0 _ (ILit l) = (g0, Right $ ConsNode (showILit l) []) extendGraph g0 env (IFCall (mn,c,_) es) | mn == "Prelude" && c == "unknown" && null es = (g0, Right FreeNode) | otherwise = let (g1,ns) = extendGraphL g0 env es in (g1, Right $ FuncNode c ns) extendGraph g0 env (ICCall (_,c,_) es) = let (g1,ns) = extendGraphL g0 env es in (g1, Right $ ConsNode c ns) extendGraph g0 env (IFPCall (_,c,_) m es) = let (g1,ns) = extendGraphL g0 env es in (g1, Right $ PartNode c (PartFuncCall m) ns) extendGraph g0 env (ICPCall (_,c,_) m es) = let (g1,ns) = extendGraphL g0 env es in (g1, Right $ PartNode c (PartConsCall m) ns) extendGraph g0 env (IOr e1 e2) = let (g1,[n1,n2]) = extendGraphL g0 env [e1,e2] in (g1, Right $ ChoiceNode (maxNodeID g1) n1 n2) -- TODO: better choice ids extendGraphL :: Graph -> IEnv -> [IExpr] -> (Graph,[NodeID]) extendGraphL g0 _ [] = (g0,[]) extendGraphL g0 env (e:es) = let (g1,n1) = extendGraph g0 env e (g2,n ) = either (\nid -> (g1,nid)) (\nd -> addNode nd g1) n1 (g3,ns) = extendGraphL g2 env es in (g3, n:ns) -- Shows a literal as a string. Used in the interpreter to avoid -- specific graph nodes for literal values. showILit :: ILiteral -> String showILit (IInt n) = show n showILit (IChar c) = show c showILit (IFloat f) = show f ------------------------------------------------------------------------------ -- The following operations retrieves some static information of programs. -- In principle, they can be evaluated at compile time. -- Since efficiency is not the objective of this interpreter, -- we compute everything at run time. -- Returns the function with a given (unqualified) name. funcOf :: String -> [IFunction] -> IFunction funcOf fn [] = error $ "Function '" ++ fn ++ "' not found!" funcOf fn (fd@(IFunction (_,f,_) _ _ _ _) : funs) = if fn==f then fd else funcOf fn funs -- Returns the arity of a given function name. arityOf :: String -> [IFunction] -> Int arityOf fn prog = let IFunction _ ar _ _ _ = funcOf fn prog in ar -- Returns the body of a given function name. bodyOf :: String -> [IFunction] -> IFuncBody bodyOf fn prog = let IFunction _ _ _ _ b = funcOf fn prog in b -- Returns the demanded argument of a given function name. demandOf :: String -> [IFunction] -> Maybe Int demandOf fn prog = case d of [] -> Nothing [i] -> Just i _ -> error $ "Function '" ++ fn ++ "' has more than one demanded argument (not yet supported)" where IFunction _ _ _ d _ = funcOf fn prog -- Computes an expression representing the choice structure demanded -- by the function of the given node id. choiceOfDemand :: State -> NodeID -> Maybe IExpr choiceOfDemand st nid = case lookupNode nid (graph st) of FuncNode f _ -> choiceOfBody (bodyOf f (program st)) _ -> error "choiceOfDemand: no function node in control" where choiceOfBody (IFuncBody (IBlock _ _ stm)) = choiceOfStmt stm choiceOfBody (IExternal _) = Nothing choiceOfStmt stm = case stm of ICaseCons _ bs -> if null bs then Nothing else Just (foldr1 (\e1 e2 -> IOr e1 e2) (map branchesToConsFree bs)) _ -> error "choiceOfDemand: function without constructor demand in control" where branchesToConsFree (IConsBranch c ar _) = ICCall c (map (\_ -> IFCall ("Prelude","unknown",0) []) [1 .. ar]) ------------------------------------------------------------------------------ -- Some standard functions which are usually defined in the prelude. -- For the moment, when we compile single modules only, we define -- them here since they are required for interpreter examples. -- apply f x: demands f and returns (f x) funApply :: IFunction funApply = IFunction ("Prelude","apply",0) 2 Public [0] (IExternal "apply") -- seq x y: demands x and returns y funSeq :: IFunction funSeq = IFunction ("Prelude","seq",0) 2 Public [0] $ IFuncBody $ IBlock [] [] (IReturn (IVarAccess 0 [1])) -- f $! x: demands x and returns (f x) funDollarBang :: IFunction funDollarBang = IFunction ("Prelude","$!",0) 2 Public [1] (IExternal "$!") -- f $$! x = f (id $! x), i.e., first f and then x is demanded, returns (f x). -- Used for computations of normal forms with left to right argument evaluation. funDollarDollarBang :: IFunction funDollarDollarBang = IFunction ("Prelude","$$!",0) 2 Public [0] $ IFuncBody $ IBlock [IVarDecl 1,IVarDecl 2] [IVarAssign 1 (IVarAccess 0 [0]),IVarAssign 2 (IVarAccess 0 [1])] (IReturn (IFCall ("Prelude","$!",0) [IVar 1, IVar 2])) -- f $# x: demands x and returns (f x) (and suspends on a free variable -- which is not yet implemented) funDollarHash :: IFunction funDollarHash = IFunction ("Prelude","$#",0) 2 Public [1] (IExternal "$#") -- normalForm x: demands x and returns the normal form of x funNormalForm :: IFunction funNormalForm = IFunction ("Prelude","normalForm",0) 1 Public [0] (IExternal "normalForm") standardFuncs :: [IFunction] standardFuncs = [ funApply, funSeq, funDollarBang, funDollarDollarBang , funDollarHash, funNormalForm ] ------------------------------------------------------------------------------