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.
72 lines
2.8 KiB
Plaintext
72 lines
2.8 KiB
Plaintext
;;;; A macro's parameter list: positional names, [ ] patterns, and &.
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;;;;
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;;;; macros.flan is the other half of this and is deliberately not merged with
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;;;; it: everything there is written [& args] and picks its arguments apart by
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;;;; hand, which is what every macro in the tree looked like before this. Here
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;;;; the parameter list does the picking, and the two files together are the
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;;;; claim that both spellings are the same grammar rather than two.
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;;;;
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;;;; Nothing below checks its own arity. It cannot be reached with the wrong
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;;;; one: lib/expand.ml's check_call runs over the call *before* the macro is
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;;;; expanded, so a miscount is refused at the call with the call's own
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;;;; location — see macro-arity.flan and the three beside it.
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;; The shape the feature was asked for (DISCUSS.org): a binding vector
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;; destructured in the signature, and & for the body. Without a parameter list
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;; this is (at args 0), a match on Form.Vec to unwrap it, four more (at ...)
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;; inside that, and (form-rest args 1) for the body.
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(defmacro do-grid [[r rows c cols] & body]
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`(dotimes [~r ~rows]
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(dotimes [~c ~cols]
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~@body)))
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;; One positional parameter, which is where the grammar changed: [x] used to
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;; bind the whole argument list and now binds the first argument. The gensym is
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;; the ordinary reason it is there — expansion is not hygienic — and not
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;; anything to do with the parameter list.
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(defmacro doubled [x]
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(let [v (gensym)]
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`(let [~v ~x] (+ ~v ~v))))
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;; Patterns nest, because a pattern's elements are patterns. And & is not only
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;; the top level's: the tail of a pattern is the tail of that vector.
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(defmacro nested [[a [b c]] & body]
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`(do (print ~a) (print ~b) (print ~c) ~@body))
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;; & inside a pattern, which is the same & and means the same thing one level
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;; down: the tail of the vector written at the call.
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(defmacro first-of [[a & more]]
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`(do (print ~a) ~@more))
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;; & with nothing after it at the call: the rest is an empty slice, ~@ splices
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;; nothing, and the expansion is the wrapper alone. The arity check says "at
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;; least 1" and one is what this is given.
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(defmacro shout [label & body]
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`(do (print ~label) ~@body (println "!")))
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;; The whole argument list, which is what [args] used to mean and is now spelled
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;; [& args]. Every macro in the tree was migrated to this line, so it is the
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;; one that has to keep working unchanged.
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(defmacro all-of [& args]
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(if (= (length args) 0)
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`true
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`(if ~(at args 0) (all-of ~@(form-rest args 1)) false)))
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(defn main [] i32
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(do-grid [i 2 j 3]
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(print i) (print j))
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(println "")
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(print (doubled 21)) (println "")
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(nested [1 [2 3]] (println " nested"))
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(first-of [4 (print " and") (println " more")])
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(shout "alone")
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(shout "with" (print " body"))
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(print (all-of)) (print " ")
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(print (all-of true true true)) (print " ")
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(print (all-of true false true)) (println "")
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0)
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