clojure

问题 Instead of zip-mapping two lists to get: (zipmap ["a","b","c"] ["c","d","e"]) = {"c" "e", "b" "d", "a" "c"} I want to concatenate the first element of the first list with the first element of the second list and so on to get: ("ce","bd","ac") or in the reverse order. 回答1: You can do that with map . map can take multiple collections, it takes the next element from each collection and passes them into the function passed as the first argument (stopping when one of the collections runs out). So

问题 Probably an easy one for anyone who actually knows how to write macros in any Lisp. I want to be able to define synonyms for function names. I've been copy-and-paste hacking core.clj to do this, but I don't want to be such a dunce forever! It seems obvious a macro that rewrites the call to a synoym-function into a call to the original function is the right way to do it. 回答1: If I understand your question, there's an easier way: def the new symbol to the old function. user=> (def foo +) #'user

问题 How to cast a character to int in Clojure? I am trying to write a rot 13 in clojure, so I need to have something to cast my char to int. I found something called (int), so I put: (int a) Get: CompilerException java.lang.RuntimeException: Unable to resolve symbol: a in this context, compiling:(NO_SOURCE_PATH:13:1) Then I put: (int 'a) Get: ClassCastException clojure.lang.Symbol cannot be cast to `java.lang.Character clojure.lang.RT.intCast (RT.java:1087) Then: (rot13 ''a') Get:

问题 How to cast a character to int in Clojure? I am trying to write a rot 13 in clojure, so I need to have something to cast my char to int. I found something called (int), so I put: (int a) Get: CompilerException java.lang.RuntimeException: Unable to resolve symbol: a in this context, compiling:(NO_SOURCE_PATH:13:1) Then I put: (int 'a) Get: ClassCastException clojure.lang.Symbol cannot be cast to `java.lang.Character clojure.lang.RT.intCast (RT.java:1087) Then: (rot13 ''a') Get:

问题 In Clojure, if I have a function f , (defn f [& r] ... ) and I have a seq args with the arguments I want to call f with, I can easily use apply : (apply f args) Now, say I have another function g , which is designed to take any of a number of optional, named arguments - that is, where the rest argument is destructured as a map: (defn g [& {:keys [a b] :as m}] ... ) I'd normally call g by doing something like (g :a 1 :b 2) but if I happen to have a map my-map with the value {:a 1 :b 2}, and I

问题 Every so often I find myself wanting to apply a collection of functions on several collections of parameters. It's easy to do with map and a very simple function. (map (fn invoke [f & args] (apply f args)) [- + *] [1 2 3] [1 2 3] [1 2 3]) (-1 6 27) Searching the web turns up quite a few libraries that define a similar function, often called funcall or invoke. Because of Clojure's penchant for variadic functions, I cannot help but think there should already be a default version of this

问题 Every so often I find myself wanting to apply a collection of functions on several collections of parameters. It's easy to do with map and a very simple function. (map (fn invoke [f & args] (apply f args)) [- + *] [1 2 3] [1 2 3] [1 2 3]) (-1 6 27) Searching the web turns up quite a few libraries that define a similar function, often called funcall or invoke. Because of Clojure's penchant for variadic functions, I cannot help but think there should already be a default version of this

问题 If I do this: ('a 'b 'c) I get this: c Why? 回答1: The link Hauleth posted is a good overview to symbols but the answer to your question is that calling a symbol as a function is equivalent to looking that symbol up in the first argument. ('a 'b) is equivalent to (get 'b 'a) The documentation for get shows that you can pass an optional third argument as the default. In your example 'c is treated as the default and returned since 'b is not a map and 'a can't be found. 来源： https://stackoverflow

问题 Say I have the sequence: [1 2 3 4 5] And I want to map over them in the pairs: [(1, 2), (2, 3), (3, 4), (4, 5)] I have tried: (map f (partition 2 [1 2 3 4])) But this results in the sequence of pairs: [(1, 2), (3, 4)] How can I get the desired functionality? 回答1: By default partiton returns non-overlapping partitions, but you can supply a step argument to provide the offset at which partitions are created: clojure.core/partition ([n coll] [n step coll] [n step pad coll]) Returns a lazy

问题 Is it possible to append a value to an attribute using enlive? example: I have this <a href="/item/edit/">edit</a> and would like this <a href="/item/edit/123">edit</a> I am currently doing this: (html/defsnippet foo "views/foo.html" [:#main] [ctxt] [:a] (html/set-attr :href (str "/item/edit/" (ctxt :id)))) But I would prefer not to embed the URL into my code, by just appending the id to the existing URL (html/defsnippet foo "views/foo.html" [:#main] [ctxt] [:a@href] (html/append (ctxt :id)))