-- mget m k ?? d — one-line extract-with-default for map lookup.
--
-- `mget` returns an Optional (nil if the key is missing). Combined with
-- `??` you get a terse default in a single statement:
--
-- v = mget m k ?? 0
--
-- The parser is arity-aware: `mget` takes exactly 2 args, so `??` binds
-- to the whole `(mget m k)` result, not to the key. No need to bind the
-- raw lookup into a temporary first. Works for literal keys, variable
-- keys, path-access keys, call-result keys, parenthesised keys, and any
-- value type (numbers, text, lists, maps).
-- Literal key, value present.
hit>n;m=mset mmap "k" 5;mget m "k" ?? 0
-- Literal key, value missing — default applies.
miss>n;m=mmap;mget m "missing" ?? 99
-- Variable key, value present.
varkey>n;m=mset mmap "k" 5;k="k";mget m k ?? 0
-- Variable key, missing — default applies.
varkey-miss>n;m=mmap;k="missing";mget m k ?? 7
-- Text-typed value with a text default.
textval>t;m=mset mmap "k" "hi";mget m "k" ?? "default"
-- Text default reached when the key is absent.
textval-miss>t;m=mmap;mget m "absent" ?? "default"
-- Path-access key — `ks.0` is evaluated as the key, then `?? 0` applies
-- to the whole `mget` result.
pathkey>n;m=mset mmap "k" 5;ks=["k"];mget m ks.0 ?? 0
-- run: hit
-- out: 5
-- run: miss
-- out: 99
-- run: varkey
-- out: 5
-- run: varkey-miss
-- out: 7
-- run: textval
-- out: hi
-- run: textval-miss
-- out: default
-- run: pathkey
-- out: 5