A File is a path-backed jfile record: (instance? java.io.File f) is true,
str/slurp coerce it to its path, and the File method surface (getName/
getPath/exists/isDirectory/isFile/listFiles/getParent) dispatches through
record-method-dispatch. slurp/spit/flush run over Chez's filesystem
primitives; file-seq's dir primitives (__file?/__dir?/__list-dir) and the
overlay's File branch (.isDirectory/.listFiles, which emit to jolt-host-call)
are jfile-aware. clojure.java.io/file + as-file are def-var!'d natively.
New host/chez/io.ss, a Chez-native implementation -- the seed's
clojure.java.io (io.clj) is a Janet-backed shim over janet.*/janet.file, so
it can't be reused. The analyzer resolves io/file because the seed ctx has
clojure.java.io loaded; only a runtime def-var! is needed. type/instance-
check/str-render/jolt-host-call are extended via the set!-wrap pattern (type
also re-def-var!'d since the var cell captured the old value).
Reader/StringReader-coupled io (io/reader, line-seq over a file, .toURL,
slurp over a reader) deferred to jolt-at0a.
Parity 2176 -> 2191, 0 new divergences. New test/chez/_io.janet 20/20.
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