Joseph Ferano
242f8c2047
The refusal list was rewritten and the prologues that pointed at it were not, so prelude.ml claimed in three places that what it now contains is impossible: the splitting header said `split` is refused at the foot of the file, forty lines above `split`; the ASCII-case header said Odin's allocating to_lower is not available here, next to the one that was written; and the UTF-8 header said the rest of core/strings is refused rather than ported. Each keeps its point rather than losing it. The iterator is still the shape that owns nothing and still the right call when there is no result to own; lower-ascii and bytes-ci=? are still the right calls when a copy is not wanted, since folding a comparison over two inputs beats lowering both. What changed is the reason, which used to be the absence of an allocator and is now a choice between two shapes that both exist. And strings.flan told the reader the opposite of what it did -- "not freed", on the line above the free. vec.flan already had the right framing: the free is written, it keeps the block because an arena cannot release one, and that is the difference the capability set exists to state.
155 lines
6.5 KiB
Plaintext
155 lines
6.5 KiB
Plaintext
;;;; The prelude's second tier: the functions that return new storage.
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;;;;
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;;;; Every one of these was refused by name in prelude.ml until there was an
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;;;; allocator to return a Vec from, and this file is the corpus that says the
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;;;; refusals are lifted. The cases are chosen the way the slice-algorithm
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;;;; tests were: each is an input a plausible wrong version gets wrong.
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;;;;
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;;;; Everything allocated here is freed, even though leaking is defined
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;;;; behaviour (spec-memory.md), because this file is the example people copy.
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;;; A (Vec u8) printed as text, without the caller writing the two-step every
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;;; time. as-slice borrows -- it copies ptr+len and never the elements -- so v
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;;; is still the owner afterwards and is still free-able.
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(defn show [v (Ptr (Vec u8))]
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(println (string (as-slice (deref v)))))
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(defn main [] i32
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;; The builder. Three appends and two numbers into one Vec, which is the
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;; case the shared static scratch buffer in the runtime makes impossible for
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;; i64->bytes on its own: two of its results cannot be held at once, and
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;; these two numbers are both in the answer.
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(let [b (vec-new u8)]
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(append! (addr b) (bytes "x="))
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(append-i64! (addr b) 42)
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(append! (addr b) (bytes " y="))
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(append-i64! (addr b) -7)
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(append! (addr b) (bytes " r="))
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(append-f64! (addr b) 1.5)
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(show (addr b)) ; x=42 y=-7 r=1.5
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(free b))
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;; concat over three parts, and over none -- the empty result rather than a
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;; trap.
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(let [parts [(bytes "one") (bytes "") (bytes "two")]]
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(let [c (concat (slice parts 0 3))]
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(show (addr c)) ; onetwo
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(free c)))
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(let [parts [(bytes "unused")]]
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(let [c (concat (slice parts 0 0))]
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(println (len c)) ; 0
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(free c)))
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;; join: n parts, n-1 separators. The one-part case is the one that must not
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;; emit a separator at all, and the zero-part case is the one a "append then
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;; chop the tail" join gets wrong because there is no tail.
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(let [parts [(bytes "a") (bytes "b") (bytes "c")]]
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(let [j (join (slice parts 0 3) (bytes ", "))]
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(show (addr j)) ; a, b, c
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(free j))
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(let [j (join (slice parts 0 1) (bytes ", "))]
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(show (addr j)) ; a
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(free j))
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(let [j (join (slice parts 0 0) (bytes ", "))]
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(println (len j)) ; 0
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(free j))
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;; An empty separator is concat.
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(let [j (join (slice parts 0 3) (bytes ""))]
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(show (addr j)) ; abc
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(free j)))
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;; repeat, including zero times.
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(let [r (repeat-bytes (bytes "ab") 3)]
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(show (addr r)) ; ababab
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(free r))
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(let [r (repeat-bytes (bytes "ab") 0)]
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(println (len r)) ; 0
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(free r))
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;; The allocating case pair. The input is a string literal, which lives in
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;; .rodata -- an in-place lower would either segfault at -O0 or be deleted at
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;; -O2, and that is exactly why these exist. Digits and punctuation pass
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;; through untouched, which is the range check a table-free version gets
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;; wrong by shifting every byte.
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(let [l (to-lower (bytes "Hello, World 42!"))]
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(show (addr l)) ; hello, world 42!
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(free l))
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(let [u (to-upper (bytes "Hello, World 42!"))]
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(show (addr u)) ; HELLO, WORLD 42!
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(free u))
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;; replace. "aaa" with "aa" -> "b" is the non-overlapping rule: the answer is
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;; "ba", because the match consumes both a's and the scan resumes after them.
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(let [r (replace-bytes (bytes "aaa") (bytes "aa") (bytes "b"))]
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(show (addr r)) ; ba
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(free r))
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;; A replacement longer than what it replaces, and one that is empty.
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(let [r (replace-bytes (bytes "a,b,c") (bytes ",") (bytes " -- "))]
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(show (addr r)) ; a -- b -- c
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(free r))
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(let [r (replace-bytes (bytes "a,b,c") (bytes ",") (bytes ""))]
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(show (addr r)) ; abc
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(free r))
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;; No occurrence is a copy, and an empty `from` is a copy -- the reading
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;; where it matches everywhere is an infinite loop.
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(let [r (replace-bytes (bytes "abc") (bytes "z") (bytes "!"))]
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(show (addr r)) ; abc
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(free r))
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(let [r (replace-bytes (bytes "abc") (bytes "") (bytes "!"))]
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(show (addr r)) ; abc
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(free r))
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;; split. n separators, n+1 fields, always -- so the trailing empty field is
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;; present, which is where Odin's own iterator and its allocating split
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;; disagree with each other.
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(let [f (split (bytes "a,b,c") \,)]
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(println (len f)) ; 3
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(println (string (at f 0))) ; a
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(println (string (at f 2))) ; c
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(free f))
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(let [f (split (bytes "a,b,") \,)]
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(println (len f)) ; 3
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(println (len (at f 2))) ; 0
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(free f))
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(let [f (split (bytes ",a") \,)]
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(println (len f)) ; 2
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(println (len (at f 0))) ; 0
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(free f))
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;; No separator at all is one field, and the empty input is one empty field.
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(let [f (split (bytes "abc") \,)]
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(println (len f)) ; 1
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(println (string (at f 0))) ; abc
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(free f))
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(let [f (split (bytes "") \,)]
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(println (len f)) ; 1
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(println (len (at f 0))) ; 0
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(free f))
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;; The fields are slices of the input and nothing was copied: this one
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;; round-trips through join, and the separator it rebuilds with is a
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;; different one, so an implementation that handed back the original slice
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;; would print the original string.
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(let [f (split (bytes "a,b,c") \,)]
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(let [j (join (as-slice f) (bytes "/"))]
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(show (addr j)) ; a/b/c
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(free j))
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(free f))
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;; The allocator is the context's, so with-allocator moves the whole tier
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;; into an arena -- which is the answer to the fixed arity of a defn, and the
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;; reason none of these takes an allocator argument. free-all is what
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;; releases the region, and arena-destroy hands it back.
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(let [a (arena-new 4096)]
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(with-allocator a
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(let [parts [(bytes "in") (bytes "arena")]]
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(let [j (join (slice parts 0 2) (bytes "-"))]
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(show (addr j)) ; in-arena
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;; The free is written because the binding is dead after it either
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;; way, and it keeps the block: an arena cannot release one, which
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;; is the difference the capability set exists to state. free-all
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;; below is what actually releases this.
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(free j))))
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(free-all a)
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(arena-destroy a))
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0)
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