"Calling a function with a bad signature!" when I forget to specify iter's out type

[jruderman]

Assertion failed: ((i >= FTy->getNumParams() || FTy->getParamType(i) == Params[i]->getType()) && "Calling a function with a bad signature!"), function init, file /Users/graydon/src/llvm/lib/VMCore/Instructions.cpp, line 191.

iter z() {
    put 0u;
}