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Pattern grammar: _, symbol, atom (number/string/keyword/bool), (), and (p1 ... pn) list patterns (recursive). Symbols become fresh vars in a fresh form, atoms become literals to unify against, lists recurse position-wise. Repeated names produce the same fresh var (so they unify by ==). Macro is built with explicit cons/list rather than a quasiquote because the quasiquote expander does not recurse into nested lambda bodies — the natural `\`(matche-clause (quote ,target) cl)` spelling left literal `(unquote target)` forms in the output. 14 tests, 222/222 cumulative. Phase 5 done (project, conda, condu, onceo, nafc, matche all green).
75 lines
2.3 KiB
Plaintext
75 lines
2.3 KiB
Plaintext
;; lib/minikanren/matche.sx — Phase 5 piece D: pattern matching over terms.
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;;
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;; (matche TARGET
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;; (PATTERN1 g1 g2 ...)
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;; (PATTERN2 g1 ...)
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;; ...)
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;;
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;; Each clause unifies TARGET with PATTERN, introducing a fresh variable
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;; for every plain symbol in the pattern, and runs its goal body. The
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;; pattern grammar:
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;;
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;; _ wildcard — fresh anonymous var
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;; x plain symbol — fresh var, bind by name
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;; ATOM literal (number, string, keyword, boolean) — must equal
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;; () empty list — must equal
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;; (p1 p2 ... pn) list pattern — recurse on each element
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;;
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;; The macro expands to a `conde` whose clauses are
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;; `((fresh (vars...) (== target pat-expr) body...))`.
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;;
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;; Fixed-length list patterns only — no rest patterns. To match "head + rest",
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;; use `(fresh (a d) (conso a d target) body)` directly.
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;;
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;; Note: the macro builds the expansion via `cons` / `list` rather than a
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;; quasiquote — the quasiquote expander does not recurse into lambda
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;; bodies, which broke the natural `\`(matche-clause (quote ,target) cl)`
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;; spelling.
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(define matche-symbol-var? (fn (s) (symbol? s)))
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(define
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matche-collect-vars
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(fn (pat) (matche-collect-vars-acc pat (list))))
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(define
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matche-collect-vars-acc
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(fn
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(pat acc)
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(cond
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((matche-symbol-var? pat)
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(if (some (fn (s) (= s pat)) acc) acc (append acc (list pat))))
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((and (list? pat) (not (empty? pat)))
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(reduce (fn (a p) (matche-collect-vars-acc p a)) acc pat))
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(:else acc))))
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(define
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matche-pattern->expr
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(fn
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(pat)
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(cond
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((matche-symbol-var? pat) pat)
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((and (list? pat) (empty? pat)) (list (quote list)))
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((list? pat) (cons (quote list) (map matche-pattern->expr pat)))
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(:else (list (quote quote) pat)))))
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(define
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matche-clause
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(fn
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(target cl)
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(let
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((pat (first cl)) (body (rest cl)))
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(let
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((vars (matche-collect-vars pat)))
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(let
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((pat-expr (matche-pattern->expr pat)))
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(list
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(cons
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(quote fresh)
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(cons vars (cons (list (quote ==) target pat-expr) body)))))))))
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(defmacro
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matche
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(target &rest clauses)
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(cons (quote conde) (map (fn (cl) (matche-clause target cl)) clauses)))
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