Clojure简单模式匹配
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作为我上一个问题的跟进，我试图在Clojure中实现一个简单的模式匹配。
我想要以下内容：
(match target
[ub] expr1 ; ub should be bound to actual value in expr1
[\'< ub] expr2 ; match the literal less-than symbol
; and ub should be bound to actual value in expr2
[lb ub] expr3 ; lb and ub should be bound to actual values in expr3
:else expr4 ; default case if none match
)
(match [< 5.0] ...)
expr2
let
\'<
[\'< ub]
(let [[sym1 ub] pattern]
(if (= \'< sym1)
expr1)
(range-case target
[0.0 < 1.0] :greatly-disagree
[< 2.0] :disagree
[< 3.0] :neutral
[< 4.0] :agree
[5.0] :strongly-agree
42 :the-answer
:else :do-not-care)
[...]
[ub] (if previous-ub `(and (<= ~previous-ub ~target) (<= ~target ~ub))
`(< ~target ~ub))
[\'< ub] (if previous-ub `(and (<= ~previous-ub ~target) (< ~target ~ub))
`(< ~target ~ub))
[lb ub] `(and (<= ~lb ~target) (<= ~target ~ub))
[\'< lb ub] `(and (< ~lb ~target) (<= ~target ~ub))
[lb \'< ub] `(and (<= ~lb ~target) (< ~target ~ub))
[\'< lb \'< ub] `(and (< ~lb ~target) (< ~target ~ub))
cond
没有找到相关结果
已邀请:
1 个回复
版萍层分
和，因为两者都不包含可能会失败的支票。因此，始终会选择第一个。 这是代码：(defn make-clause [expr-g [spec expr & more :as clause]] (when (seq clause) (let [tests-and-bindings (map (fn [x] (if-not (symbol? x) (let [x-g (gensym \"x\")] [`(= ~x ~x-g) x-g]) [nil x])) spec) tests (keep first tests-and-bindings) bindings (map second tests-and-bindings)] `(let [[~@bindings] ~expr-g] (if (and (= (count ~expr-g) ~(count spec)) ~@tests) ~expr ~(make-clause expr-g more)))))) (defmacro match [expr & clauses] (let [expr-g (gensym \"expr\")] `(let ~[expr-g expr] ~(make-clause expr-g clauses))))(let [expr98 [(quote <) 3.0]] (let [[ub] expr98] (if (and (= (count expr98) 1)) (if previous-ub (and (<= previous-ub target) (<= target ub)) (< target ub)) (let [[x99 ub] expr98] (if (and (= (count expr98) 2) (= (quote <) x99)) (if previous-ub (and (<= previous-ub target) (< target ub)) (< target ub)) (let [[lb ub] expr98] (if (and (= (count expr98) 2)) (and (<= lb target) (<= target ub)) nil)))))))(match [\'< 3.0] [ub] (if previous-ub (and (<= previous-ub target) (<= target ub)) (< target ub)) [\'< ub] (if previous-ub (and (<= previous-ub target) (< target ub)) (< target ub)) [lb ub] (and (<= lb target) (<= target ub))))