feature request: if function with only "then" in expr

[porres]

the if function in expr needs two arguments, one for "then" and other for "else"

I was hoping for the option of just having the "then" function with only one argument. In this case, the "else" expression would be inexistent and ignored, that is it won't have any output.

[porres]

maybe a new "ifthen" function?

something:

[expr ifthen($f1 > 0, 1)]

would then only output a "1" if the input is > 0

[umlaeute]

if it doesn't generate any output, then it's no longer an expression.
quoting wikipedia:

An expression in a programming language is a combination of one or more constants, variables, operators, and functions that the programming language interprets [...] and computes to produce ("to return", in a stateful environment) another value.

[danfuzz]

I'd like to petition for this issue to be reopened. I understand that there is a "mathematical purity" to guaranteeing that all expr outlets emit values. However, as a practical matter, it would be very useful to have this functionality, thereby being able to avoid a bunch of boilerplate off of an expr output (e.g. having two outputs, one a boolean, and using that to perform a select).

[porres]

there's a new issue now: #663

[danfuzz]

Thanks. I saw #663, but I think doing this original issue would be better: What I find myself wanting is, for example, things like a three-output expr where just one of them is possibly not output per incoming execution.