*in*, read-line, read, with-in-str, and line-seq land as a new overlay IO
tier (core/50-io.clj). *in* is a dynamic var holding a reader — a plain map
of two closures, :read-line-fn (next line, nil at EOF) and :read-fn (next
form, advancing past exactly that form). The default *in* reads real stdin
with a shared leftover buffer, so read and read-line interleave correctly;
with-in-str rebinds *in* to a string reader over one atom-held buffer —
(read) consumes its form, a following (read-line) returns the rest of that
line, as in Clojure. read has the 0/1/3 arities (EOF throws, or returns
eof-value when eof-error? is false).
The Janet seed grows two seams next to read-string: __stdin-read-line (one
line off stdin, newline stripped) and __parse-next (one form off a string ->
[form rest], nil at end of input) — and loses the line-seq stub.
Two traps hit and documented for future tiers: a map LITERAL with :jolt/type
as a key is read as a tagged form (don't tag overlay value maps), and a
leftover seed stub holding the same name breaks direct-linked self-recursion
— the overlay line-seq's recursive call bound to the stub's root, truncating
after one line. The stub's string-splitting behavior is kept as a documented
extension.
20 new io-spec rows (read-line EOF/interleave, read arities + eval round-trip,
line-seq incl. real-stdin paths). Gate green: conformance 326x3, suite 4577,
full jpm test.
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