Joseph Ferano
d6fc15474b
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.
77 lines
3.7 KiB
Plaintext
77 lines
3.7 KiB
Plaintext
;;;; The clock and the environment.
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;;;;
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;;;; Every line of output here is an invariant and not a reading, and that is
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;;;; forced rather than chosen: this file is in the corpus @x86 builds twice
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;;;; and diffs, and the acceptance table matches its stdout exactly, so a
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;;;; timestamp or an elapsed count would fail a correct compiler on the second
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;;;; run. What is left is what a clock actually has to promise — that it does
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;;;; not go backwards, that a sleep does not return early, that the two faces
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;;;; of one clock describe one instant — and those are the properties worth
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;;;; pinning anyway. A test that asserted "this took under 3ms" would be a
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;;;; test of the machine's load.
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(defn main [] i32
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;; Monotonic, twice. The whole contract in one line: it never goes
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;; backwards. Equal is allowed and is not a bug — two reads inside one tick
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;; of a coarse timer are the same nanosecond.
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(let [t1 (monotonic-ns)
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t2 (monotonic-ns)]
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(println (>= t2 t1)))
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;; And the origin is the first read rather than boot, so the first readings
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;; a program takes are small. Bounded rather than pinned, and the bound is
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;; deliberately loose: what separates this clock from a boot-relative one is
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;; hours, so a minute proves it and a second only proved it on hardware. The
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;; tighter bound was a reading after all — memcheck runs this program on a
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;; synthetic CPU tens of times slower than the metal, the second genuinely
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;; elapsed, and the line went false under a tool that has nothing to say
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;; about clocks. A minute is past anything a simulator adds and still short
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;; of the smallest thing the assertion is meant to catch.
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(println (< (monotonic-ns) (* 60 ns-per-second)))
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;; The f64 face is the i64 one divided, and what is checked is that the two
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;; describe the same instant: a later reading in seconds is at or past an
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;; earlier reading in nanoseconds converted the same way. A clock whose two
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;; faces came from different sources fails this.
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(let [a (/ (f64 (monotonic-ns)) 1000000000.0)
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b (monotonic-seconds)]
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(println (>= b a)))
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;; The wall clock is a date, so the invariant is a date one: it is after
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;; 2020 and before 2100. That pins the epoch and the unit at once — a clock
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;; counting microseconds, or counting from boot, fails both halves.
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(let [now (unix-seconds)]
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(println (and (> now 1577836800.0) (< now 4102444800.0))))
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;; Sleep is specified as *at least*, so at-least is what is asserted; the
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;; upper bound belongs to the scheduler and not to this language. Two
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;; milliseconds because the shortest sleep a default kernel actually
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;; performs is a timer tick, and a shorter request would make this a test of
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;; how that kernel was configured.
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(let [before (monotonic-ns)]
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(sleep-ns (* 2 ns-per-millisecond))
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(println (>= (- (monotonic-ns) before) (* 2 ns-per-millisecond))))
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;; Zero and negative return at once rather than being refused, which is what
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;; a deadline already passed produces. That they return at all is the
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;; assertion; nothing here is timed.
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(sleep-ns 0)
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(sleep-ns -1)
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(sleep-seconds 0.0)
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(println "slept")
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;; ── The environment ──────────────────────────────────────────────
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;; A variable nothing sets. None is the answer, and it is a different answer
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;; from a variable set to nothing.
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(match (getenv "FLAN_NO_SUCH_VARIABLE_AT_ALL")
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(Some v) (println "unexpectedly set")
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None (println "unset"))
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;; PATH is set for every process that gets as far as running this, and the
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;; only portable thing about its contents is that there are some.
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(match (getenv "PATH")
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(Some v) (println (> (length v) 0))
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None (println "no PATH"))
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0)
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