added system.finished for first class iterators

compiler/ast.nim

@@ -344,7 +344,7 @@ type
     nfSem       # node has been checked for semantics
 
   TNodeFlags* = set[TNodeFlag]
-  TTypeFlag* = enum   # keep below 15 for efficiency reasons (now: 14)
+  TTypeFlag* = enum   # keep below 17 for efficiency reasons (now: 16)
     tfVarargs,        # procedure has C styled varargs
     tfNoSideEffect,   # procedure type does not allow side effects
     tfFinal,          # is the object final?

compiler/lambdalifting.nim

@@ -692,13 +692,6 @@ proc liftIterator*(iter: PSym, body: PNode): PNode =
   stateAsgnStmt.add(newIntTypeNode(nkIntLit, -1, getSysType(tyInt)))
   result.add(stateAsgnStmt)
 
-# TODO:
-# - nested iterators
-# - arglist as a type
-# - tyIterator everywhere
-# - 'finished' builtin
-# - 'start' builtin (XXX copy Lua's terminology?)
-
 proc liftIterSym*(n: PNode): PNode =
   # transforms  (iter)  to  (let env = newClosure[iter](); (iter, env)) 
   result = newNodeIT(nkStmtListExpr, n.info, n.typ)

compiler/parser.nim

@@ -1473,7 +1473,7 @@ proc simpleStmt(p: var TParser): PNode =
   case p.tok.tokType
   of tkReturn: result = parseReturnOrRaise(p, nkReturnStmt)
   of tkRaise: result = parseReturnOrRaise(p, nkRaiseStmt)
-  of tkYield: result = parseYieldOrDiscard(p, nkYieldStmt)
+  of tkYield: result = parseReturnOrRaise(p, nkYieldStmt)
   of tkDiscard: result = parseReturnOrRaise(p, nkDiscardStmt)
   of tkBreak: result = parseBreakOrContinue(p, nkBreakStmt)
   of tkContinue: result = parseBreakOrContinue(p, nkContinueStmt)

compiler/semexprs.nim

@@ -1173,6 +1173,8 @@ proc SemYield(c: PContext, n: PNode): PNode =
       SemYieldVarResult(c, n, restype)
     else:
       localError(n.info, errCannotReturnExpr)
+  elif c.p.owner.typ.sons[0] != nil:
+    localError(n.info, errGenerated, "yield statement must yield a value")
 
 proc lookUpForDefined(c: PContext, i: PIdent, onlyCurrentScope: bool): PSym =
   if onlyCurrentScope: 

compiler/semstmts.nim

@@ -818,7 +818,7 @@ proc semIterator(c: PContext, n: PNode): PNode =
   result = semProcAux(c, n, skIterator, iteratorPragmas)
   var s = result.sons[namePos].sym
   var t = s.typ
-  if t.sons[0] == nil:
+  if t.sons[0] == nil and s.typ.callConv != ccClosure:
     LocalError(n.info, errXNeedsReturnType, "iterator")
   # iterators are either 'inline' or 'closure'; for backwards compatibility,
   # we require first class iterators to be marked with 'closure' explicitly