Need a way to pass parameters by reference in Calc

[rlwhitcomb]

Say I want to pass in a list/array or map/object to be modified inside a function. Currently that doesn't work:

list = [] -> [ ]
Defining function addTo(a, n) = {
   a += n
}
addTo(list, 1)
Error: Cannot change Parameter value a at line 3.

Suggest allowing var or const (default) as a modifier in front of the name, as in:

define a(var a, const n) = { ... }

where the default would be const (as now), but either one is allowed in order to be explicit.

Of course, this would imply that the actual value for a non-const parameter could not be a constant value...

[rlwhitcomb]

Okay, apart from the difficulties I'm having just implementing this, there is at least one (likely) insoluble problem: when an empty set/map is converted to one or the other when the first element is added. Even in the best case when I could get the real object and make a new one, the original reference (in the symbol table of one of the callers) is never referenced anywhere, so I could never update the original reference with the new object, unless I could pass in the original LValueContext of it ... (good luck with that). But, then again, maybe this is the crux of the whole situation: passing a valid LValueContext around as the "value" of the parameter. I don't seem to be "getting" it yet ....

[rlwhitcomb]

Questions:

• At what point do we find the actual symbol table reference(s) to the lvalue to do the assignment, += or whatever?
• What do we need to pass as the "value" in the ParameterValue to get that to happen?
• How to indicate the proper lookup context (i.e., say the "real" variable is named "s" in the global context, but the parameter name is "s" inside the function, how do we reference the "real" "s" value [that is, we need the caller's context to do the lookup)?
• And even more, it may be a complicated indexing, membership with multiple variables, and string expressions, etc. They all need the calling context to do the evaluation.
• But, at what point can later parameters reference earlier parameter values in our rules to this point?? Ever?? Need to figure out.