copilot-c99: Refactor variable update functionality. Refs #431.

The previous commit introduced functionality for handling array arguments in
trigger argument functions as a special case. The special-casing needed to
handle array arguments in trigger argument functions is nearly identical to the
special-casing needed in stream generator functions. This patch refactors the
code to share the special-casing in common between the two sorts of functions.

Author: RyanGlScott

copilot-c99/src/Copilot/Compile/C99/CodeGen.hs

@@ -163,17 +163,24 @@ mkStep cSettings streams triggers exts =
     (triggerDeclns, triggerStmts) =
       unzip $ map mkTriggerCheck triggers
 
+    -- Update the value of a variable with the result of calling a function that
+    -- generates the next value in a stream expression. If the type of the
+    -- variable is an array, then we cannot perform a direct C assignment, so
+    -- we instead pass the variable as an output array to the function.
+    updateVar :: C.Ident -> C.Ident -> Type a -> C.Expr
+    updateVar varName genName (Array _) =
+      C.Funcall (C.Ident genName) [C.Ident varName]
+    updateVar varName genName _ =
+      C.AssignOp C.Assign (C.Ident varName) (C.Funcall (C.Ident genName) [])
+
     -- Write code to update global stream buffers and index.
     mkUpdateGlobals :: Stream -> (C.Decln, C.Stmt, C.Stmt, C.Stmt)
     mkUpdateGlobals (Stream sId buff _expr ty) =
       (tmpDecln, tmpAssign, bufferUpdate, indexUpdate)
         where
           tmpDecln = C.VarDecln Nothing cTy tmpVar Nothing
 
-          tmpAssign = case ty of
-            Array _ -> C.Expr $ C.Funcall (C.Ident $ generatorName sId)
-                                          [ C.Ident tmpVar ]
-            _       -> C.Expr $ C.Ident tmpVar C..= val
+          tmpAssign = C.Expr $ updateVar tmpVar (generatorName sId) ty
 
           bufferUpdate = case ty of
             Array _ -> C.Expr $ memcpy dest (C.Ident tmpVar) size
@@ -193,7 +200,6 @@ mkStep cSettings streams triggers exts =
           tmpVar   = streamName sId ++ "_tmp"
           buffVar  = C.Ident $ streamName sId
           indexVar = C.Ident $ indexName sId
-          val      = C.Funcall (C.Ident $ generatorName sId) []
           cTy      = transType ty
 
     -- Make code that copies an external variable to its local one.
@@ -273,18 +279,11 @@ mkStep cSettings streams triggers exts =
 
                 assign :: C.Ident -> C.Ident -> UExpr -> C.Expr
                 assign aTempName aArgName (UExpr { uExprType = ty }) =
-                  case ty of
-                    Array _ -> argCall aArgName [C.Ident aTempName]
-                    _       -> C.AssignOp C.Assign
-                                          (C.Ident aTempName)
-                                          (argCall aArgName [])
+                  updateVar aTempName aArgName ty
 
                 aArgNames :: [C.Ident]
                 aArgNames = take (length args) (argNames name)
 
-                argCall :: C.Ident -> [C.Expr] -> C.Expr
-                argCall name' = C.Funcall (C.Ident name')
-
                 -- Build an expression to pass a temporary variable as argument
                 -- to a trigger handler.
                 --

copilot-c99/src/Copilot/Compile/C99/Compile.hs

@@ -119,9 +119,8 @@ compileC cSettings spec = C.TransUnit declns funs
         accessDecln (Stream sId buff _ ty) = mkAccessDecln sId ty buff
 
         streamGen :: Stream -> C.FunDef
-        streamGen (Stream sId _ expr ty@(Array _)) =
-          mkGenFunArray (generatorName sId) (generatorOutputArgName sId) expr ty
-        streamGen (Stream sId _ expr ty) = mkGenFun (generatorName sId) expr ty
+        streamGen (Stream sId _ expr ty) =
+          exprGen (generatorName sId) (generatorOutputArgName sId) expr ty
 
         triggerGen :: Trigger -> [C.FunDef]
         triggerGen (Trigger name guard args) = guardDef : argDefs
@@ -131,9 +130,18 @@ compileC cSettings spec = C.TransUnit declns funs
 
             argGen :: String -> UExpr -> C.FunDef
             argGen argName (UExpr ty expr) =
-              case ty of
-                Array _ -> mkGenFunArray argName (argName ++ "_output") expr ty
-                _       -> mkGenFun argName expr ty
+              exprGen argName (argName ++ "_output") expr ty
+
+        -- Create a function that calculates the current value generated by an
+        -- expression `expr` of type `ty`. The generator treats arrays
+        -- specially, and the function takes an output array as a parameter.
+        -- The second identifier `outputArrName` is not used if `expr` is not an
+        -- array.
+        exprGen :: C.Ident -> C.Ident -> Expr a -> Type a -> C.FunDef
+        exprGen funName outputArrName expr ty@(Array _) =
+          mkGenFunArray funName outputArrName expr ty
+        exprGen funName _ expr ty =
+          mkGenFun funName expr ty
 
 -- | Generate the .h file from a 'Spec'.
 compileH :: CSettings -> Spec -> C.TransUnit