No-space arguments

I believe have agreed that

f r.x

(with no spaces around the dot, and no parens around r.x) means

f (r.x)

That is, treat it consistently with qualified names. I asked everyone to express a view; Iavor, Eric, Arnaud, Joachim, and Richard all said it was at least acceptable; others expressed no view. So let’s take that as a decision, at least for now.

Naked selectors

Next question: how should we treat a “naked selector”, namely .x where there is no space after the dot, but there is a space before. I think there are three viable choices:

It’s simply illegal. This defers the choice; perhaps later we will have more experience to go on.
It’s a postfix operator, binding less tightly than function application, but more tightly than any infix operator. So then (r .x) means r.x, and (r .x .y) means r.x.y. But (f r .x) means (f r).x.

This choice naturally supports chaining (nice to have, but not essential). We can write

f .map double

.filter isEven

meaning (f.map double).filter isEven

It’s a postfix operator, binding more tightly than function application, just as record update does. So then (f r .x) means (f r.x), and (f r .x .y s .z) means (f r.x.y s.z).

This choice allows us to regard our decision about (f r.x) as what naturally happens if we parse it as three lexemes: f, r, and .x. But it also breaks the “function application binds more tightly than anything else” rule, just as (f r {x=3}) sadly does already.

It does not permit chaining, at least not without stacked-up parens.

In all three cases we allow (.x), meaning (\r. r.x). For (2) and (3) we can regard it as a “section”, like infix operators only simpler because there is no argument.

I think this is the last major question we have to answer.

What are your views? Personally I lean towards (2), but I could certainly live with (1). I’m a bit reluctant to adopt (3).

Simon