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Allow rest-patterns in pattern2 and prevent unification with nil

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Jeremy Dormitzer 2019-09-11 00:45:03 -04:00
parent ff302d078a
commit 06a7bc3c60
1 changed files with 6 additions and 0 deletions
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src/sicp_logic/match.clj
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@ -54,10 +54,16 @@
;; If the patterns are already equal, the frame already ;; If the patterns are already equal, the frame already
;; has the correct bindings ;; has the correct bindings
(= pattern1 pattern2) frame (= pattern1 pattern2) frame
;; Nothing should unify with nil
(or (nil? pattern1) (nil? pattern2)) :failed
;; If pattern1 is a rest-pattern (e.g. [& ?rest]), unify its rest ;; If pattern1 is a rest-pattern (e.g. [& ?rest]), unify its rest
;; part with pattern2 in the current frame ;; part with pattern2 in the current frame
(and (sequential? pattern1) (= (first pattern1) '&)) (and (sequential? pattern1) (= (first pattern1) '&))
(unify-match (second pattern1) pattern2 frame) (unify-match (second pattern1) pattern2 frame)
;; If pattern2 is a rest-pattern, unify its rest part with pattern1
;; in the current frame
(and (sequential? pattern2) (= (first pattern2) '&))
(unify-match (second pattern2) pattern1 frame)
;; If pattern1 is a variable, try to bind it to pattern2 ;; If pattern1 is a variable, try to bind it to pattern2
(var? pattern1) (extend-if-possible pattern1 pattern2 frame) (var? pattern1) (extend-if-possible pattern1 pattern2 frame)
;; If pattern1 is not a variable but pattern2 is, try to bind ;; If pattern1 is not a variable but pattern2 is, try to bind