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.
119 lines
5.4 KiB
Plaintext
119 lines
5.4 KiB
Plaintext
;;;; The prelude's in-place slice algorithms.
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;;;;
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;;;; Every input here is chosen so that a wrong implementation passes nothing.
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;;;; The sort input is unsorted, has duplicates, has negatives and has an odd
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;;;; length, so a comparison with the wrong sense, an off-by-one that drops the
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;;;; last element, and a swap that loses an equal key all show up. The second
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;;;; sort is reverse-sorted, which is the worst case for insertion sort and the
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;;;; case a no-op comparison would pass. The third sorts a *subslice* and then
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;;;; prints the whole owning array: a slice is ptr+len into its owner, so the
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;;;; five elements inside the range must be sorted and the three outside it
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;;;; must be untouched. That last one is the property that dies silently if a
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;;;; slice parameter ever starts being copied.
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(defonce xs [7 i32])
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(defonce ys [5 i32])
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(defonce zs [8 i32])
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(defn show [s [i32]] ()
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(dotimes [i (length s)]
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(when (> i 0) (print " "))
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(print (at s i)))
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(println ""))
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(defn load-xs [] ()
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(set (at xs 0) 5)
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(set (at xs 1) -3)
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(set (at xs 2) 5)
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(set (at xs 3) 0)
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(set (at xs 4) 12)
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(set (at xs 5) -3)
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(set (at xs 6) 7))
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(defn main [] i32
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(load-xs)
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(show (slice xs 0 (length xs))) ; 5 -3 5 0 12 -3 7
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;; Reading the whole slice, before anything reorders it.
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(print (sum-i32 (slice xs 0 (length xs)))) (println "") ; 23
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(print (match (min-of (slice xs 0 (length xs))) (Some v) v None 99))
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(println "") ; -3
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(print (match (max-of (slice xs 0 (length xs))) (Some v) v None 99))
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(println "") ; 12
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;; First index, not the last: 5 appears at 0 and at 2.
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(print (match (index-of (slice xs 0 (length xs)) 5) (Some v) v None -1))
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(println "") ; 0
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(print (match (index-of (slice xs 0 (length xs)) 4) (Some v) v None -1))
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(println "") ; -1
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;; An empty slice has no least element, and None is the answer.
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(print (match (min-of (slice xs 3 3)) (Some v) v None 99))
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(println "") ; 99
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;; Reverse of an odd-length slice: the middle element stays put.
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(reverse (slice xs 0 (length xs)))
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(show (slice xs 0 (length xs))) ; 7 -3 12 0 5 -3 5
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;; And of a two-element one, the smallest case that can actually move.
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(reverse (slice xs 0 2))
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(show (slice xs 0 (length xs))) ; -3 7 12 0 5 -3 5
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(load-xs)
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(sort (slice xs 0 (length xs)))
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(show (slice xs 0 (length xs))) ; -3 -3 0 5 5 7 12
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;; Reverse-sorted: the case a comparison that never fires would pass.
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(set (at ys 0) 5) (set (at ys 1) 4) (set (at ys 2) 3)
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(set (at ys 3) 2) (set (at ys 4) 1)
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(sort (slice ys 0 (length ys)))
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(show (slice ys 0 (length ys))) ; 1 2 3 4 5
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;; A subslice, with the elements on both sides left alone.
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(set (at zs 0) 100) (set (at zs 1) 9) (set (at zs 2) -1)
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(set (at zs 3) 9) (set (at zs 4) 4) (set (at zs 5) 0)
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(set (at zs 6) 200) (set (at zs 7) 300)
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(sort (slice zs 1 6))
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(show (slice zs 0 (length zs))) ; 100 -1 0 4 9 9 200 300
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;; Degenerate lengths must do nothing rather than run off an end.
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(sort (slice zs 0 0))
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(reverse (slice zs 0 0))
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(sort (slice zs 2 3))
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(reverse (slice zs 2 3))
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(show (slice zs 0 (length zs))) ; 100 -1 0 4 9 9 200 300
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;; ── The short arities ──────────────────────────────────────────────
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;; (slice a) and (slice a n) are (slice a 0 (length a)) and
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;; (slice a n (length a))
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;; written out in the checker, so each line here is read against the
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;; spelling above it that it stands for. A fixed array does not decay to a
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;; slice at a call, so passing one to a function over [$t] is what these
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;; exist for.
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(load-xs)
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(show (slice xs)) ; 5 -3 5 0 12 -3 7
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(show (slice xs 4)) ; 12 -3 7
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;; Of a slice rather than of an array: the length is the slice's own, so
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;; these index from where the previous one started, not from the array's 0.
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(show (slice (slice xs))) ; 5 -3 5 0 12 -3 7
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(show (slice (slice xs 2) 1)) ; 0 12 -3 7
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;; A literal array is nobody's named place, and it still slices: the two
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;; lines the author hit are these, one sorting through the prelude's
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;; generic [$t] sort and one over character literals.
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(sort (slice [6 2 4 9 1 9 4 5]))
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(let [a [6 2 4 9 1 9 4 5]]
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(sort (slice a))
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(show (slice a))) ; 1 2 4 4 5 6 9 9
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(let [cs [\I \N \S \E \R \T \I \O \N \S \O \R \T]]
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(sort (slice cs))
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(println (string (slice cs)))) ; EIINNOORRSSTT
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;; ── Strings ────────────────────────────────────────────────────────
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;; A string is ptr+len over bytes, so it indexes to a byte and slices to a
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;; string viewing the same bytes. No copy, and no route through [u8].
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(let [s "insertion"]
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(print (at s 0)) (println "") ; 105
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(println (slice s)) ; insertion
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(println (slice s 6)) ; ion
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(println (slice s 0 6))) ; insert
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(println (slice "sorted" 2 4)) ; rt
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0)
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