Syntax question: to let or not to let

[nikomatsakis]

In the current dada syntax, if you use = you declare a new variable:

x = 22

and if you use :=, you can reassign an existing place:

x := 23
y.field := 23

I was going for an extremely "lightweight" syntax reminiscent of Python, but to be honest, I'm not sure I like it. I am thinking maybe it's better to follow Rust (and, I realize, Java/TypeScript?) precedent here and use let:

let x = 22

and then just use = for reassignment:

x = 23
y.field = 23

Thoughts?

[nikomatsakis]

This probably makes parsing easier too, as you would presumably write

let x: Type

and

let atomic x

Right now we need a bit of goofy lookahead to handle these cases.

[vemoo]

I prefer having let, it's easier to see where new bindings are being introduced.

[nikomatsakis]

@vemoo want to try implementing it?

[vemoo]

sure

[brson]

I also prefer keywords to introduce variables. I think it's because it's a strong visual indicator that new state is being created.

[vemoo]

this was implemented in #221