let-in if do-expr is problematic? (was: Re: proposal: let in if parentheses)

[Claude Pache]

> Le 21 août 2018 à 21:20, Herbert Vojčík <herby at mailbox.sk> a écrit :
> 
> Hi!
> 
> It would be nice to know if do expressions have some a chance, otherwise some other syntax for let-in would be really helpful, especially now that we have arrow functions.
> 
> I would propose to use different variant of let (maybe also const):
> 
> OP 1:
> 
>  let in a = b(), if (a) a.c();
> 
> OP 2:
> 
>  let in a = b(), if (a) c(a);
> 
> Instead of
>  const big = raw => {
>    let cooked = cook(raw);
>    return consumer => {
>      // do things with consumer and cooked
>    };
>  };
> 
>  const big = raw =>
>    let in cooked = cook(raw), consume => {
>      // do things with consumer and cooked
>    };
> 
> In short,
> 
>  let in binding = expr, stmt|expr
> 
> It may work for `const in` as well.
> 
> Herby
> 
> P.S.: Alternative syntax is "let a=3, b=4, ..., in foo(a,b,c,d)" but this can only tell late if it is plain let-up-to-end-of-scope or local-scope-let, so not sure if that may be a problem; OTOH you can chain more of them and resembles classical let-in better.

Please, don’t take it too seriously: but have you thought about resuscitating the (in)famous `with` statement?

```js
const big = raw => 
    do with ({cooked: cook(raw)})
        consumer => {
            // do things with consumer and cooked
        };;
```

And no the two ”;”s are not a typo: I need to end both the `with` statement and the `const` declaration.

But more seriously... those sorts of “clever” syntaxes (`let-in` or `do-with` or whatever), apart from complicating the language, are in danger of raising as much issues than they’re resolving; the double-semicolon oddity is one of them.

—Claude