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.
62 lines
2.6 KiB
Plaintext
62 lines
2.6 KiB
Plaintext
;;;; (slice-from-ptr p n) — NEXT.md, "a pointer from C needs a length before it
|
|
;;;; can be indexed". The motivating pointers come from C, but nothing about
|
|
;;;; the form does: a (Ptr T) is a (Ptr T) whoever made it, so this case makes
|
|
;;;; its own with (addr (at a 0)) and needs no library and no window.
|
|
;;;;
|
|
;;;; What is asserted, line by line:
|
|
;;;;
|
|
;;;; - the length is the one the caller stated, and (length s) answers it;
|
|
;;;; - the elements read through are the same storage, not a copy — the last
|
|
;;;; two lines write through the slice and read the array back, which is
|
|
;;;; the whole ptr+len claim;
|
|
;;;; - a shorter promise than the truth is legal and is what indexing then
|
|
;;;; believes, because the caller's number is the only length there is;
|
|
;;;; - the result is an ordinary [T]: it slices, it is passed to a function
|
|
;;;; that takes a slice, and the prelude's algorithms work on it.
|
|
;;;;
|
|
;;;; What is NOT here, and is in test_flan.ml's refusal table instead: a
|
|
;;;; negative literal length, a first argument that is not a pointer, and
|
|
;;;; (free (slice-from-ptr ...)) — a slice owns nothing, so free refuses it by
|
|
;;;; the rule it already had.
|
|
|
|
(defonce a [5 i32])
|
|
|
|
(defn total [s [i32]] i32
|
|
(let [acc 0]
|
|
(dotimes [i (length s)]
|
|
(set acc (+ acc (at s i))))
|
|
acc))
|
|
|
|
(defn main [] ()
|
|
(dotimes [i 5]
|
|
(set (at a i) (* (+ i 1) 10)))
|
|
|
|
;; The whole array, as the caller promises it: five elements behind the
|
|
;; address of the first.
|
|
(let [s (slice-from-ptr (addr (at a 0)) 5)]
|
|
(println (length s)) ; 5
|
|
(println (at s 0)) ; 10
|
|
(println (at s 4)) ; 50
|
|
(println (total s)) ; 150
|
|
;; An ordinary [i32] from here on: slice it, and the sub-view still points
|
|
;; into the same storage.
|
|
(println (total (slice s 1 3)))) ; 50
|
|
|
|
;; A promise shorter than the truth. Nothing complains — there is nothing to
|
|
;; complain with — and the length the caller gave is the length indexing and
|
|
;; the bounds check both use.
|
|
(let [s (slice-from-ptr (addr (at a 1)) 2)]
|
|
(println (length s)) ; 2
|
|
(println (total s))) ; 50
|
|
|
|
;; Zero is a length like any other. An empty slice is not a null pointer and
|
|
;; is not an error.
|
|
(println (length (slice-from-ptr (addr (at a 0)) 0))) ; 0
|
|
|
|
;; It is a view, not a copy: a write through the slice is a write to the
|
|
;; array, and this is what would fail if the form ever grew a memcpy.
|
|
(let [s (slice-from-ptr (addr (at a 0)) 5)]
|
|
(set (at s 2) 7)
|
|
(println (at a 2)) ; 7
|
|
(println (total s)))) ; 127
|