void type for generics

compiler/semexprs.nim

@@ -36,16 +36,6 @@ proc semExprWithType(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
     GlobalError(n.info, errExprXHasNoType, 
                 renderTree(result, {renderNoComments}))
 
-proc semExprWithTypeNoDeref(c: PContext, n: PNode, 
-                            flags: TExprFlags = {}): PNode = 
-  result = semExpr(c, n, flags)
-  if result.kind == nkEmpty: 
-    # do not produce another redundant error message:
-    raiseRecoverableError()
-  if result.typ == nil:
-    GlobalError(n.info, errExprXHasNoType, 
-                renderTree(result, {renderNoComments}))
-
 proc semSymGenericInstantiation(c: PContext, n: PNode, s: PSym): PNode =
   result = symChoice(c, n, s)
   

compiler/semtypes.nim

@@ -581,8 +581,12 @@ proc semProcTypeNode(c: PContext, n, genericParams: PNode,
       addSon(result.n, newSymNode(arg))
       addSon(result, typ)
   if n.sons[0].kind != nkEmpty: 
-    result.sons[0] = paramType(c, n.sons[0], genericParams, cl)
-    res.typ = result.sons[0]
+    var r = paramType(c, n.sons[0], genericParams, cl)
+    # turn explicit 'void' return type into 'nil' because the rest of the 
+    # compiler only checks for 'nil':
+    if skipTypes(r, {tyGenericInst}).kind != tyEmpty:
+      result.sons[0] = r
+      res.typ = result.sons[0]
 
 proc semStmtListType(c: PContext, n: PNode, prev: PType): PType = 
   checkMinSonsLen(n, 1)

tests/accept/compile/tvoid.nim

@@ -0,0 +1,13 @@
+discard """
+  output: "he, no return type; a string"
+"""
+
+proc ReturnT[T](): T =
+  when T is void:
+    echo "he, no return type;"
+  else:
+    result = " a string"
+
+ReturnT[void]()
+echo ReturnT[string]()
+

todo.txt

@@ -6,7 +6,12 @@ Version 0.8.14
   * add ``modGet`` for generics
   * documentation
   * provide ``mod`` as an alternative syntax for ``var``
-- document Nimrod's two phase symbol lookup for generics
+- document:
+  * Nimrod's two phase symbol lookup in generics
+  * type constraints for generics
+  * void type
+  * ``is`` operator for type equivalence
+  
 - optional indentation for 'case' statement
 - make threadvar efficient again on linux after testing
 - test the sort implementation again

web/news.txt

@@ -39,6 +39,8 @@ Language Additions
 ------------------
 
 - Added new ``is`` and ``of`` operators.
+- The built-in type ``void`` can be used to denote the absense of any type.
+  This is only needed in generic contexts.
 
 
 Compiler Additions