Joel de Guzman: ...
This:
lambda( _x, _y, _z = 123 )[ ... ]
will be transformed to this:
lambda( _x = _1, _y = _2, _z = 123 )[ ... ]
I wonder though if it's a good idea to separate the signature from the locals:
lambda( _x, _y )[ let( _z = 123 )[ ... ] ]
seems to be more "idiomatic"? No?
Under my mental model of the "new lambda", these two are not the same. _z = 123 in the lambda initializes _z to 123 once when the lambda is defined; let _z = 123 declares _z to be 123 each time the lambda is called. That is, the outer _z is a member variable, the inner _z is a local temporary. So, if we return to my generator example that was to yield 1, 2, 3 on successive calls, it would be spelled lambda( _a = 0 )[ ++_a ] as I first expected. Incidentally, you might consider supporting a scopeless let (if it doesn't already work): lambda(_x, _y)[ let( _z = _x + _y ), _z * _z ] analogous to a C++ local variable: auto _z = _x + _y; return _z * _z; and maybe even dispense with the let at all: lambda(_x, _y)[ _z = _x + _y, _z * _z ] although this has the usual drawback with being ambiguous with an assignment to an outer-scope _z: lambda( _x, _y, _z = 0 )[ _z = _x + _y, _z * _z ]