Code refactoring

README.md

@@ -55,6 +55,13 @@ In the following, we describe various uses of the `icurry` tool.
    
        > icurry -v Prog
 
+   As a default, the ICurry compiler lifts all nested case/let expressions,
+   i.e., it transforms them into auxiliary top-level operations.
+   This is also necessary for the simple interpreter contained in this
+   package (see below).
+   If an implementation of ICurry can deal with nested case/let expressions,
+   one can use the option `--nolifting` to supress this lifting.
+
 2. One can also use a simple (i.e., not efficient) interpreter
    to execute ICurry programs and visualize their behavior.
    In this case, one has to provide the name of a 0-ary function `mymain`

src/ICurry/Compiler.curry

@@ -157,14 +157,12 @@ trFunc opts (Func qn@(mn,fn) ar vis _ rule) =
  where
   optsf = opts { optFun = qn }
 
-  demandOf (External _) = [] -- TODO
-  demandOf (Rule args rhs) = case rhs of
-    Case _ ce _ -> case ce of
-      Var v -> maybe (funError optsf "case variable not in left-hand side")
-                     (\i -> [i])
-                     (elemIndex v args)
-      _     -> []
-    _ -> []
+-- Computes (approximates) the arguments demanded by a rule.
+demandOf :: Rule -> [Int]
+demandOf (External _) = [] -- TODO
+demandOf (Rule args rhs) = case rhs of
+  Case _ (Var v) _ -> maybe [] (: []) (elemIndex v args)
+  _                -> []
 
 trRule :: ICOptions -> Rule -> IFuncBody
 trRule _ (External s) = IExternal s

src/ICurry/Main.curry

@@ -30,7 +30,7 @@ testI p =
 banner :: String
 banner = unlines [bannerLine,bannerText,bannerLine]
  where
-   bannerText = "ICurry Compiler (Version of 09/02/20)"
+   bannerText = "ICurry Compiler (Version of 13/02/20)"
    bannerLine = take (length bannerText) (repeat '=')
 
 main :: IO ()
@@ -74,7 +74,7 @@ processOptions argv = do
          (putStr (unlines opterrors) >> printUsage >> exitWith 1)
   when (optHelp opts) (printUsage >> exitWith 0)
   when (not (null (optMain opts)) && not (optLift opts)) $ error
-    "Incompatible options: nested case/let must be lifted for the interpreter"
+    "Incompatible options: interpreter requires case/let lifting!"
   return (opts, map stripCurrySuffix args)
  where
   printUsage = putStrLn (banner ++ "\n" ++ usageText)
@@ -106,7 +106,7 @@ options =
            "command to view PDF files (default: 'evince')"
   , Option "i" ["interactive"]
            (NoArg (\opts -> opts { optInteractive = True }))
-           "interactive execution (ask after each result or step)"
+           "interactive execution (ask after each step/result)"
   , Option "" ["nolifting"]
            (NoArg (\opts -> opts { optLift = False }))
            "do not lift nested case/let expressions"

src/ICurry/Types.curry

@@ -41,9 +41,12 @@ data IProg = IProg String [String] [IDataType] [IFunction]
 data IDataType = IDataType IQName [(IQName,IArity)]
   deriving (Show, Read)
 
---- An ICurry function declaration consisting of the function's name, arity,
---- the positions of always demandeded arguments (0 = first argument),
---- and a body.
+--- An ICurry function declaration consisting of the function's name,
+--- arity, visibility, the positions of always demandeded arguments
+--- (where 0 denotes the first argument), and a body.
+--- Note that the demanded arguments are definitely required to
+--- evaluate the function. In some situations (e.g., complex nested case
+--- statements), more arguments might be demanded.
 data IFunction = IFunction IQName IArity IVisibility [Int] IFuncBody
   deriving (Show, Read)
 
@@ -71,12 +74,13 @@ data IBlock = IBlock [IVarDecl] [IAssign] IStatement
 --- In the subsequent assignments, graph nodes will be assigned to
 --- these variables. Instead of explicitly handling free variables,
 --- one could also use local variables and assign a node representing
---- a value generator operation. Since different implementations
---- might you different strategies to deal with free variables,
---- ICurry supports both options.
+--- a value generator operation for this free variable.
+--- Since different implementations might use different strategies
+--- to deal with free variables, ICurry supports both options.
 ---
---- NOTE: The ICurry variable with index 0 always points to the root
---- of the left-hand side when an ICurry function is invoked.
+--- NOTE: The ICurry code assumes that the ICurry variable with index 0
+--- always points to the root of the left-hand side when an ICurry function
+--- is invoked. This invariant must be ensured by the ICurry application!
 data IVarDecl = IVarDecl  IVarIndex
               | IFreeDecl IVarIndex
   deriving (Show, Read)