next steps for first class iterators

compiler/ccgstmts.nim

@@ -114,13 +114,15 @@ proc genGotoState(p: BProc, n: PNode) =
 
 proc genBreakState(p: BProc, n: PNode) =
   var a: TLoc
-  initLocExpr(p, n.sons[0], a)
   if n.sons[0].kind == nkClosure:
     # XXX this produces quite inefficient code!
+    initLocExpr(p, n.sons[0].sons[1], a)
+    lineF(p, cpsStmts, "if (($1->Field0) < 0) break;$n", [rdLoc(a)])
+  else:
+    initLocExpr(p, n.sons[0], a)
     # the environment is guaranteed to contain the 'state' field at offset 0:
     lineF(p, cpsStmts, "if ((((NI*) $1.ClEnv)[0]) < 0) break;$n", [rdLoc(a)])
-  else:
+  #  lineF(p, cpsStmts, "if (($1) < 0) break;$n", [rdLoc(a)])
-    lineF(p, cpsStmts, "if (($1) < 0) break;$n", [rdLoc(a)])
 
 proc genSingleVar(p: BProc, a: PNode) =
   var v = a.sons[0].sym

compiler/lambdalifting.nim

@@ -692,6 +692,28 @@ 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)
+  let iter = n.sym
+  assert iter.kind == skIterator
+  var env = copySym(getHiddenParam(iter))
+  env.kind = skLet
+
+  var v = newNodeI(nkVarSection, n.info)
+  addVar(v, newSymNode(env))
+  result.add(v)
+  # add 'new' statement:
+  result.add(newCall(getSysSym"internalNew", env))
+  result.add makeClosure(iter, env, n.info)
+
 proc liftForLoop*(body: PNode): PNode =
   # problem ahead: the iterator could be invoked indirectly, but then
   # we don't know what environment to create here: 
@@ -763,10 +785,10 @@ proc liftForLoop*(body: PNode): PNode =
 
   loopBody.sons[0] = v2
   var bs = newNodeI(nkBreakState, body.info)
-  if not env.isNil:
+  #if not env.isNil:
-    bs.addSon(indirectAccess(env, 
+  #  bs.addSon(indirectAccess(env, 
-      newSym(skField, getIdent":state", env, env.info), body.info))
+  #    newSym(skField, getIdent":state", env, env.info), body.info))
-  else:
+  #else:
-    bs.addSon(call.sons[0])
+  bs.addSon(call.sons[0])
   loopBody.sons[1] = bs
   loopBody.sons[2] = body[L-1]

compiler/semstmts.nim

@@ -406,7 +406,10 @@ proc semFor(c: PContext, n: PNode): PNode =
   openScope(c.tab)
   n.sons[length-2] = semExprNoDeref(c, n.sons[length-2], {efWantIterator})
   var call = n.sons[length-2]
-  if call.kind notin nkCallKinds or call.sons[0].kind != nkSym or
+  if call.kind in nkCallKinds and call.sons[0].typ.callConv == ccClosure:
+    # first class iterator:
+    result = semForVars(c, n)
+  elif call.kind notin nkCallKinds or call.sons[0].kind != nkSym or
       call.sons[0].sym.kind != skIterator: 
     if length == 3:
       n.sons[length-2] = implicitIterator(c, "items", n.sons[length-2])

compiler/transf.nim

@@ -113,6 +113,8 @@ proc newAsgnStmt(c: PTransf, le: PNode, ri: PTransNode): PTransNode =
   result[1] = ri
 
 proc transformSymAux(c: PTransf, n: PNode): PNode =
+  if n.sym.kind == skIterator and n.sym.typ.callConv == ccClosure:
+    return liftIterSym(n)
   var b: PNode
   var tc = c.transCon
   if sfBorrow in n.sym.flags: 

tests/run/titer8.nim

@@ -3,9 +3,18 @@ discard """
 1
 2
 3
-ta da1
+ta da1 1
-2
+1 2
-3'''
+1 3
+2 1
+2 2
+2 3
+3 1
+3 2
+3 3
+0
+1
+2'''
 """
 # Test first class iterator:
 
@@ -44,8 +53,27 @@ proc inProc() =
     stdout.write(word)
 
   for c in count3():
-    echo c
+    for d in count3():
+      echo c, " ", d
 
 
 inProc()
 
+iterator count0(): int {.closure.} =
+  # note: doesn't require anything in its closure (except 'state')
+  yield 0
+ 
+iterator count2(): int {.closure.} =
+  # note: requires 'x' in its closure
+  var x = 1
+  yield x
+  inc x
+  yield x
+
+# a first class iterator has the type 'proc {.closure.}', but maybe
+# it shouldn't:
+proc invoke(iter: proc(): int {.closure.}) =
+  for x in iter(): echo x
+
+invoke(count0)
+invoke(count2)

todo.txt

@@ -53,7 +53,8 @@ version 0.9.XX
 - JS gen:
   - fix exception handling
 - object branch transitions can't work with the current 'reset'; add a 'reset'
-  with an additional parameter
+  with an additional parameter --> re-evaluate this issue after constructors
+  have been added
 - fix remaining closure bugs:
   - test evals.nim with closures
   - what about macros with closures?
@@ -143,7 +144,8 @@ Version 2 and beyond
   troublesome, but maybe we can come up with a simple heuristic. (All procs
   that `new` shared memory are syncGC() candidates...)
 
-- const ptr/ref
+- const ptr/ref  --> pointless because of aliasing; 
+  much better: 'writes: []' effect
 
 - language change: inheritance should only work with reference types, so that
   the ``type`` field is not needed for objects! --> zero overhead aggregation