bug#66816: [PATCH] Delete redundant lambdas around unary functions

[Stefan Monnier]

The patch looks good to me.

> We could also have the compiler η-reduce automatically. I investigated this
> very briefly some time ago. Maybe I can dig up the patch.
> One problem is that the arity isn't necessarily preserved.

And even if we check the arity before performing the rewrite, the arity
at compile-time may be different from the arity at run-time, so it's not
a safe optimization.

OTOH we could emit a warning :-)

> Most of the time this isn't a problem but it could be something to
> watch out for if doing the η-reduction by hand.

I've been bitten a few times, indeed.


        Stefan