Hi, Racket Discourse.
I was browsing the examples of the proposed conditional syntax in this paper, [The Ultimate Conditional Syntax](https://dl.acm.org/doi/pdf/10.1145/3689746).
I have not read the formal claims and proofs they make, but the shape of things is intriguing, and it got me wondering about what I would like from the "ultimate conditional".
Arguably, `match` and friends, not to forget the behemoth, `cond`, are already more than any programmer might ask for; it is, however, fun to speculate.
So, stealing some ideas from the paper, and without stating that this is necessarily _better_, I would propose something like this:
```scheme
; cond-case, which is like `cond`
(choose
[is (blue? x) and is (red? y)
then (orange)]
[is (red? x) and is (blue? y)
then (purple)]
[else (yellow)])
; match-case, which is like `match`
(choose
[(choose
[is (odd? a) then (list 1 2)]
[else (list 2 1)]
) is (list x y)
and
b is (list u v)
then (list x u)]
[(choose
[is (even? a) then (cons 1 2)]
[else (cons 2 1)]
) is (cons x y)
and
b is (cons u v)
then (list y v)]
[else (list a b)])
```
The basic form of `choose` is:
```scheme
(choose ...+)
```
where `` is of the form `[ then ]`, or possibly in the final branch, of the form `[else ]`. Finally, each `` is of the form ` {and } ...`. The `` would be the same as with `cond` and so on.
Each `` can be one of two flavors:
- `is x` (where `x` is either true-thy or false)
- `x is y` (where `x` is some value and `y` is a `match` pattern)
What I like about this, is that it reads quite easily (in these simple cases) and it combines `cond` and `match` quite elegantly, **but** it seems like it could become a soup of words quite quickly.
* * *
Edit: what about plurals, eh?
```scheme
(choose
[are (even? x y z) then 'all-even])
; is synonym to something like
(choose
[is (even? x) and is (even? y) and is (even? z) then 'all-even])
(choose
[(x y z) are ((? integer?) (? symbol?) (? string?))
then 'integer-symbol-string])
; is synonym to
(choose
[x is (? integer?) and y is (? symbol?) and z is (? string?)
then 'integer-symbol-string])
```
* * *
Edit: and then you could specialize on the verb! [Latin](https://users.monash.edu/~damian/papers/HTML/Perligata.html), anyone?
```scheme
(choose
[is-list (even? xs) then 'all-even])
; is synonym to
(choose
[xs is (list (? even?) ...) then 'all-even])
```
Edit: instead
```scheme
(choose
[is list of (blue? '(blue blue blue))
then 'blues]
[else
'sunshine])
;=> 'blues
```
which expands into a `for/and` in terms of the `` to range over, being `list` in this case, thus:
```scheme
(for/and ([tmp (in-list vals)]) (pred? tmp))
```
* * *
What do you think about this, and more interestingly, what would _your_ fantasy conditional look like, if any?
* * *
Edit: _chef's kiss_
* * *
## Edit: it's alive!
>
---
Enough faffing about with the original post; I apologize if this is poor taste, I have been having quite the blast.
```scheme
#lang racket
(require rackunit choose)
(check-equal?
(choose
[is (integer? 1) then 'integer]
[else
#false])
'integer
"cond-like: `is` ")
(check-equal?
(choose
[are (integer? 1 2 3) then 'integers]
[else
#false])
'integers
"cond-like: `are` ")
(define x #s(node inside))
(check-equal?
(choose
[x is `#s(node ,inside) then inside]
[else
#false])
'inside
"match-like: `is`