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.
89 lines
3.2 KiB
Plaintext
89 lines
3.2 KiB
Plaintext
;; Function values, the non-escaping kind: a code address and no environment
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;; beside it. Capture does not exist, so nothing here can outlive anything.
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;;
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;; This is a Lisp-1 — one top-level namespace, enforced — so a bare function
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;; name *is* the function and there is no #' to write.
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(defn double [x i32] i32 (* x 2))
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(defn negate [x i32] i32 (- 0 x))
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(defn square [x i32] i32 (* x x))
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;; The shape map/filter/reduce want: the function arrives as a parameter, is
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;; called, and is never stored.
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(defn each [xs [i32] f (Fn [i32] i32)] ()
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(dotimes [i (length xs)]
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(set (at xs i) (f (at xs i)))))
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(defn fold [xs [i32] f (Fn [i32] i32)] i32
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(let [t 0]
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(dotimes [i (length xs)]
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(set t (+ t (f (at xs i)))))
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t))
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;; A comparator, which is the other half of what was blocked: a sort that is
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;; told the order rather than having it written in. Insertion sort, because the
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;; point here is the parameter and not the algorithm.
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(defn insertion-by [xs [i32] before? (Fn [i32 i32] bool)] ()
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(dotimes [i (length xs)]
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(let [j i]
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(while (and (> j 0) (before? (at xs j) (at xs (- j 1))))
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(swap xs j (- j 1))
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(set j (- j 1))))))
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(defn ascending [a i32 b i32] bool (< a b))
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(defn descending [a i32 b i32] bool (> a b))
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;; Returning one. A function value is a link-time constant with no environment,
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;; so handing it back up is no different from handing it down.
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(defn pick [up bool] (Fn [i32 i32] bool)
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(if up ascending descending))
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;; A function value calling another, and the transfer channel crossing an
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;; indirect call: a callee reached by pointer signals exactly as one reached by
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;; name, and the handler is established across the call.
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(defstruct TooBig [n i32])
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(defn checked [x i32] i32
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(when (> x 100) (signal (TooBig {.n x})))
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x)
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(defonce seen i32)
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;; A handler-bind and an fn literal in *one* function, which is the case that
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;; would catch the two lifted-function name sequences sharing a counter: both
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;; are lifted out of [handles] and both are numbered within it.
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(defn handles [] ()
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(handler-bind [(TooBig [c] (set seen (+ seen (.n c))))]
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(let [xs [5 200 7 300]]
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(println (fold (slice xs 0 4) checked))
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(println (fold (slice xs 0 4) (fn [x] (min x 10))))))
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(print "seen ") (print seen) (println ""))
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(defn main [] i32
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(let [xs [1 2 3 4]]
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;; A name in value position, passed down.
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(each (slice xs 0 4) double)
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(print (at xs 0)) (print " ") (print (at xs 3)) (println "")
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;; 2 + 4 + 6 + 8 negated
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(println (fold (slice xs 0 4) negate))
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;; An fn literal, whose parameter types come from the position it is in.
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(println (fold (slice xs 0 4) (fn [x] (+ x 1))))
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;; A let binding of function type, called by the name it is bound to.
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(let [f square]
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(println (f 9))))
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;; A comparator, and the same slice sorted both ways.
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(let [ys [3 1 4 1 5 9 2 6]
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s (slice ys 0 8)]
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(insertion-by s ascending)
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(print (at s 0)) (print " ") (print (at s 7)) (println "")
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(insertion-by s descending)
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(print (at s 0)) (print " ") (print (at s 7)) (println "")
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;; A returned function value, and a computed head calling it.
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(insertion-by s (pick true))
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(print (at s 0)) (println "")
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(println ((pick false) 1 2)))
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(handles)
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0)
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