fixes #404

compiler/lowerings.nim

@@ -0,0 +1,52 @@
+#
+#
+#           The Nimrod Compiler
+#        (c) Copyright 2014 Andreas Rumpf
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## This module implements common simple lowerings.
+
+const
+  genPrefix* = ":tmp"         # prefix for generated names
+
+import ast, types, idents, magicsys
+
+proc newTupleAccess*(tup: PNode, i: int): PNode =
+  result = newNodeIT(nkBracketExpr, tup.info, tup.typ.skipTypes(
+                     abstractInst).sons[i])
+  addSon(result, copyTree(tup))
+  var lit = newNodeIT(nkIntLit, tup.info, getSysType(tyInt))
+  lit.intVal = i
+  addSon(result, lit)
+
+proc addVar*(father, v: PNode) = 
+  var vpart = newNodeI(nkIdentDefs, v.info, 3)
+  vpart.sons[0] = v
+  vpart.sons[1] = ast.emptyNode
+  vpart.sons[2] = ast.emptyNode
+  addSon(father, vpart)
+
+proc newAsgnStmt(le, ri: PNode): PNode =
+  result = newNodeI(nkAsgn, le.info, 2)
+  result.sons[0] = le
+  result.sons[1] = ri
+
+proc lowerTupleUnpacking*(n: PNode; owner: PSym): PNode =
+  assert n.kind == nkVarTuple
+  let value = n.lastSon
+  result = newNodeI(nkStmtList, n.info)
+
+  var temp = newSym(skTemp, getIdent(genPrefix), owner, value.info)
+  temp.typ = skipTypes(value.typ, abstractInst)
+  incl(temp.flags, sfFromGeneric)
+
+  var v = newNodeI(nkVarSection, value.info)
+  v.addVar(newSymNode(temp))
+  result.add(v)
+  
+  result.add newAsgnStmt(newSymNode(temp), value)
+  for i in 0 .. n.len-3:
+    result.add newAsgnStmt(n.sons[i], newTupleAccess(value, i))