The author: "I think I prefer length over len, because then I'll use len as
the variable name". One arm in check.ml, one row in the table beside it, and
every (len x) in lib, test, examples, vendor, spike, docs, web, emacs,
plan.org and NEXT.md rewritten.
Shadowing and builtin/ had already taken most of the sting out: a (defn len
...) was legal and won in its own file, and builtin/len reached past it. What
was left is that len was still a builtin — the defn earned a warning, and a
wrapper had to say builtin/ at every inner call. Now there is nothing under
the short name: len is an ordinary identifier in every position, which is
what (let [len (length xs)] ...) wants.
length takes over as shadowing's worked example rather than the feature
losing one. shadow-builtin.flan, builtin-qualified.flan, pkgs/shadowed and the
builtin/ rows in test_flan move to it and go on testing shadowing.
A call to a len nothing defines is answered where an unknown function is,
after every table and after the shadowing guard, so a program with its own len
never reaches it. The sentence is said rather than guessed at — len and length
are three edits apart and the did-you-mean's net is one — and the call is
written back out through spell_arg, as-slice's spelling lifted out of it and
now shared, so what is printed compiles.
sand.flan:33 still calls the old name and is the author's to change; until it
does, test_acceptance and test_session abort there. Both were run green
against a copy with that one line changed. FIX.org says so.
A type-changing (map f) is the case into's single shadowed element name
would break if the shadowing were a trick rather than the language's
rule; it is not, because each stage is a fresh slot at its own type, and
into.flan now runs an i32 source into a (Vec f32) to say so.
A move-only accumulator carried round by recur is the shape BUILT.md
pitches the form on and was untested. It works, and recur.flan now
carries a Vec three times round and answers with it.
block's empty-body arm returned before the loop that distributes the
tail, so (do) in a tail position left ctx.tail set for whatever was
checked next. Latent rather than live — every consumer sets it
immediately before use, and the leaking form is always Unit-typed — but
it is one line to close and the invariant is easier to state closed.
Also the PORTING.md line listing loop/recur among the things with no
customer: it was built, and the half of that finding that still stands is
tail calls, which were not.
There is no TCO here and recur is not a cheaper substitute for one: the
compiler verifies the call is in the loop body's tail position, so the
mistake is a compile error where it was written rather than a stack
overflow somewhere else. A loop is a let, a While whose condition is
true, and two jumps — emit.ml is untouched, and the barrier question
recur asks is the one labelled break already answered.
Tail position is a permission that is withdrawn at the top of check, the
same read-and-withdraw defer_ok does, handed back only by a block's last
form, both arms of an if and a match arm. So nothing enumerates the forms
that are not tails, which a pre-pass over the Ast would have had to, and
would have had to keep doing.
loop is also a barrier for break and continue, which is added rather than
inherited: a loop answers with the value of its body and a jump out has
no value to give. That is also why it takes no label. A while inside a
loop keeps its own break.
Two things the shape forced. A loop binding is a plain name, because
destructuring would make recur's argument count unreadable off the
binding vector. And in_loop's "moves a value bound outside the loop"
rule had to be told about the loop's own names, or (loop [v (vec-new
i32)] ...) would have been refused for doing the ordinary thing.
