Macro
Generic switch/case macro. 'fcase' is short for 'function case'.
The 'compare-fn' is a fn of two arguments.
The 'test-expr-clauses' are value-expression pairs without surrounding parentheses, like in Clojure's 'cond'.
The 'case-value' is evaluated once and cached. Then, 'compare-fn' is called once for each clause, with the clause's test value as its first argument and 'case-value' as its second argument. If 'compare-fn' returns logical true, the clause's expression is evaluated and returned. If 'compare-fn' returns false/nil, we go to the next test value.
If 'test-expr-clauses' contains an odd number of items, the last item is the default expression evaluated if no case-value matches. If there is no default expression and no case-value matches, fcase returns nil.
See specific forms of this macro in 'case' and 're-case'.
The test expressions in 'fcase' are always evaluated linearly, in order. For a large number of case expressions it may be more efficient to use a hash lookup.
; clojure/contrib/fcase.clj:38 (defmacro fcase [compare-fn case-value & test-expr-clauses] (let [test-val-sym (gensym "test_val") test-fn-sym (gensym "test_fn") cond-loop (fn this [clauses] (cond (>= (count clauses) 2) (list 'if (list test-fn-sym (first clauses) test-val-sym) (second clauses) (this (rest (rest clauses)))) (= (count clauses) 1) (first clauses)))] (list 'let [test-val-sym case-value, test-fn-sym compare-fn] (cond-loop test-expr-clauses))))
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