How to convert a string to a function in Clojure?

Question

I've been working on Clojure question 135 Infix Calculator, basically a simplified infix to prefix arithmetic calculator:

(= 7  (__ 2 + 5))

I solved the problem as specified. But that got me wondering - what if the argument had been supplied as a string - how would I get it to work?

(= 7  (__ "2 + 5"))

Obviously I'd start with a split, then munch through the result:

(clojure.string/split "2 + 5" #"\s")
user=> ["2" "+" "5"]

But how would I convert the "+" to a function call? This isn't going to work:

("+" 2 5)
user=> java.lang.ClassCastException: java.lang.String cannot be 
cast to clojure.lang.IFn <snip>

Enlightenment sought....

DanLebrero · Accepted Answer · 2012-06-10 10:13:15Z

17

Look at the resolve function

((resolve (symbol "+")) 1 2)

answered Jun 10, 2012 at 10:13

DanLebrero

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Randall · Accepted Answer · 2012-07-12 10:31:12Z

2

you can use load-string or read-string. That's something like READ-FROM-STRING in common lisp, which adhere to the principle of 'Code is Data', treats the string as codes - evaluate and return the value.

user=> (class (load-string "+"))
clojure.core$_PLUS_
user=> (read-string "+")
+
user=>

then you can simply use it.

answered Jul 12, 2012 at 10:31

Randall

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