Joseph Ferano
9a820d86cd
The script is in tools/ rather than thrown away, because two lanes are
writing Flan in the old spelling right now and their files need the same
pass at merge.
It works on forms, not on text: a keyword becomes a dot only where it sits
in a field-label position inside a brace, so an enum member in value
position, a map key inside an EDN string and a type-position {K V} are all
left alone. :keys keeps its colon -- it names no field.
110 lines
3.9 KiB
Plaintext
110 lines
3.9 KiB
Plaintext
;;;; (Vec T) — spec-memory.md, "The four container types" and "Allocators".
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;;;;
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;;;; ptr + len + cap + allocator, owning and move-only, over one type-erased
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;;;; runtime. The element type appears nowhere in that runtime: size_of and
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;;;; align_of are produced at the call site, which without generics is simply
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;;;; the concrete call site. So this file being two element types with one
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;;;; runtime behind them is the whole claim.
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(defstruct Point [x i32 y i32])
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;;; Ownership transfers on the call. The caller's binding is dead after this,
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;;; which is what the refusal cases in test_acceptance assert.
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(defn consume [v (Vec i32)] i32
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(let [n (len v)]
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(free v)
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n))
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;;; A Vec is returned by moving it out, so the callee's binding is the
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;;; caller's. Nothing is released at function exit — there is no scope-end
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;;; anything in this language.
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(defn make [n i32] (Vec i32)
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(let [v (vec-new i32)]
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(dotimes [i n] (push v (* i i)))
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v))
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(defn sum [xs [i32]] i32
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(let [total 0]
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(dotimes [i (len xs)] (set total (+ total (at xs i))))
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total))
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(defn main [] i32
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(let [v (vec-new i32)]
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(println (len v)) ; 0
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(push v 10)
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(push v 20)
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(push v 30)
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(println (len v)) ; 3
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(println (at v 0)) ; 10
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(println (at v 2)) ; 30
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;; A Vec element is a place, and the same bounds and epoch check stands
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;; behind the value form and the place form.
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(set (at v 1) 99)
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(println (at v 1)) ; 99
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;; as-slice is a non-owning view: it copies ptr+len and never the
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;; elements, and it carries no allocator, so nothing can be freed through
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;; one. [at] and [len] over it are the array operations, unchanged.
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(println (sum (as-slice v))) ; 139
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(println (len (as-slice v 1 3))) ; 2
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(println (at (as-slice v 1 3) 0)) ; 99
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;; clone is the only copy: assignment moves. The copy is independent, and
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;; freeing it leaves the original alone.
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(let [w (clone v)]
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(set (at w 0) -1)
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(println (at w 0)) ; -1
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(println (at v 0)) ; 10
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(free w))
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;; reserve does not change the length, only the capacity, so a reserve
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;; that succeeds is invisible except that the pushes after it do not grow.
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(reserve v 64)
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(println (len v)) ; 3
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(push v 40)
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(println (len v)) ; 4
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;; The structural printer reaches both new types. Neither is followed: a
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;; Vec's elements are printed through (as-slice v), which says at the call
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;; site that it borrowed, and an allocator's contents are the runtime's and
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;; its address is not stable across runs.
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(println v) ; <vec>
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(println context/allocator) ; <allocator>
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(free v))
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;; A second element type over the same runtime, and a struct element, so
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;; that size_of and align_of are doing work rather than both being 4.
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(let [ps (vec-new Point)]
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(push ps (Point {.x 1 .y 2}))
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(push ps (Point {.x 3 .y 4}))
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(println (len ps)) ; 2
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(println (.y (at ps 1))) ; 4
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(free ps))
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;; A Vec made against an explicit allocator records it, so free and clone
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;; never need it named again. An arena cannot free one block, so this free
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;; keeps the block — releasing it is free-all's job, and that is the
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;; difference the capability set exists to state.
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(let [a (arena-new 4096)]
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(let [v (vec-new i32 a)]
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(push v 7)
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(println (at v 0)) ; 7
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(free v))
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(println (can-free? a)) ; false
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(free-all a)
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(arena-destroy a))
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;; The pushes go into whatever the context names, with nothing passed.
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(let [a (arena-new 4096)]
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(with-allocator a
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(let [v (vec-new i32)]
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(push v 5)
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(push v 6)
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(println (+ (at v 0) (at v 1))) ; 11
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(free v)))
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(arena-destroy a))
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(println (consume (make 5))) ; 5
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0)
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