advanced ffl: conditional expression then-expressions activation - conditional-statements

Question

Here is a snippet from https://github.com/anura-engine/anura/blob/55bc02244f0faba5e0831578a3c1c9a82e7bf569/src/formula_function.cpp#L923-L931:
FUNCTION_DEF(if, 2, -1, "if(a,b,c)")
const int nargs = static_cast<int>(NUM_ARGS);
for(int n = 0; n < nargs-1; n += 2) {
const bool result = EVAL_ARG(n).as_bool();
if(result) {
return EVAL_ARG(n+1);
}
}
As we can see, if there is more than one condition evaluating as true, only the then-expression corresponding to the first condition evaluating as true is returned.
Actually, only the first condition evaluating as true gets to be evaluated as true.
Meta discussing FFL, (1) would it make sense that the expression should evaluate all the conditions and return a list of all then-expressions corresponding to true conditions, as long as the inside of the whole conditional expression is free from execution triggers (bind_command, ;, etc.)? Also (2) does this exist already (obviously with a different signature)?

Answer 1

I think it could make sense for the if function to evaluate and return passing. I've only seen the 2- and 3-parameter if functions used in the wild, so I can't comment on the n-parameter version as I just found out about it. (It seems to be equivalent to "if, else if, …, else". Hunh.)
The closest syntax I know of for the list of condition/statements is something like:
on_create: "filter([
true and debug('cmd 1'),
false and debug('cmd 2'),
true and debug('cmd 3'),
], value)",
This will print 'cmd 1' and 'cmd 3' to screen.
This works because and short-circuits, and only returns the first thing to pass or the last thing to fail. The filter() call is required only if you want to use true and false, otherwise you can use true and null and drop filter(). Note that you can also use ; with this construct, I think it evaluates to a command sequence which you can use and process like a normal command. For example:
on_create: "filter([
true and debug('cmd 1'),
false and (debug('cmd 2'); debug('cmd 3')),
true and (debug('cmd 4'); debug('cmd 5')),
], value)",
Prints 'cmd 1', 'cmd 4', and 'cmd 5' to screen.
This is equivalent to:
on_create: "[
if(true, debug('cmd 1')),
if(false, debug('cmd 2'); debug('cmd 3')),
if(true, debug('cmd 4'); debug('cmd 5')),
]",
Which also prints 'cmd 1', 'cmd 4', and 'cmd 5' to screen. If you need to eliminate the null elements from the list, filter can be used as in the first example.

Answer 2

What you want is a chain of if statements. That is already easily achieved by putting multiple if statements in a row. And it is very clear and common to see in other languages. Having a custom structure for this would thus be redundant and only reduce clarity.
On the other hand, a structure to implement repeated else-if's is very useful to reduce nesting. (Excessive nesting causes readability issues and creates opportunities for confusion.)
if condition, then action
else-if condition, then action (optional)
...
else-if condition, then action (optional)
else action (optional)