Tracking issue: If/else (ternary operator)

[casey]

I propose adding an if construct, restricted by the parser to equality tests:

foo := if A == B { THEN } else { ELSE }

A, B, THEN, and ELSE are all arbitrary expressions. If A equal to B then it will evaluate as THEN, otherwise it will evaluate as ELSE.

The reason I propose adding if, restricted to equality testing, instead of a more general if, is because if, in some future in which Just get's a type system, I would like the condition, A == B above, of if to be a bool. By restricting if to equality testing, a future enhancement which adds boolean and relaxes `if's condition to be any expression would not be a breaking change.

I added the good first issue tag to this. It's tough, but I think doable for someone that's interested in learning how the lexer and parser work. The only complication I see is making sure that if isn't always parsed as a keyword, so that having a recipe named if doesn't become an error.

(See prior discussion in #262 and #674.)

[mortoray]

Perhaps an if-equal would also be useful and also be forwards compatible. Making it string based would also include the if-empty logic in it's coverage.

foo := if-equal {{bar}} "hi" { first } else { other }
nothing := if-equal {{value}} "" {first} else { other }

[casey]

I think if if-equal were introduced, it might be good to give it the fixed syntax if A == B { THAN } else { ELSE }. Since I can't imagine any syntax other than == for equality, this would also be forward compatible.

[mortoray]

I agree. It would also satisfy the if-empty need, if A == "" { THEN } else { ELSE }

[casey]

I think adding if A == B ... is definitely the right way to go. I rewrite the original post and removed mention of if-empty.

[casey]

It is done! (#714) I added both equality and inequality conditionals:

foo := if "a" == "a" { "xyz" } else { "abc" }

bar := if "a" != "b" { "xyz" } else { "abc" }

They can be used in any context where an expression was valid, so both at the top level and inside recipe interpolations.

The can only be used in expression contexts, so they can't be used to conditionally enable different parts of a justfile, like an #ifdef

I just released v0.8.2 that includes the new feature.

Thanks everyone for requesting this feature and discussing how it should work!

[mortoray]

Excellent! Thank you for adding this support.