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I'm working on a clojure program that includes these lines of code:

(defn makeStruct 
 "Take a line of input and return a starbucks-struct"
 [input]
 (let[(apply struct storeinfo (clojure.string/split input #","))]
 )

)

And am getting this compiler error:

Exception in thread "main" java.lang.IllegalArgumentException: let requires an even number of forms in binding vector (clojureHW.clj:24)

I am very new to clojure and am not entirely sure what I am doing, but in this case input is a string and I am splitting it into a vector to initialize my struct. Am I using the syntax of let incorrectly?

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3 Answers 3

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let requires an even numbers of forms, because it binds values to locals:

(let [x 10,
      y (+ x 20)]
   ; do something with x and y here
   (* x y))

Please read the documentation here: http://clojure.org/special_forms#Special%20Forms--(let%20%5Bbindings*%20%5D%20exprs*)

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5 Comments

Yes I understand that and have already been over that documentation page. I count two parts to the let statement (apply struct storeinfo) and (split input #",") What's wrong with it?
(apply struct storeinfo) is not a symbol, like x or y in the example I gave you. Btw, you have (apply struct storeinfo (clojure.string/split input #",")), not (apply struct storeinfo) and (split input #",").
The way I understood it, (apply struct storeinfo) would return a storeinfo struct that would then be split by the following statement, (split input #",") Is let the wrong keyword/operation to use here?
Yes. Maybe you mean something like -> or ->>, see for example blog.fogus.me/2009/09/04/understanding-the-clojure-macro. But if (apply struct storeinfo) is the first form that will be executed, I would expect storeinfo to be something you have defined before or a parameter of makeStruct.
Hey. If you're still watching this I posted another question about a clojure compiler error. No pressure if you can't answer. Thanks for your help.
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I think you still have misunderstanding on the lisp way handling return values and bindings.

Everything in a pair of parens an expression returns a value that value can be uses by a in a other expression or be bound to a symbol.

You have this

(apply struct storeinfo (clojure.string/split input #","))

This returnes on value because there is only one expression. Its quite simple just count the outher most parens.

And since you have nothing else in the let you have a odd number of forms (expression) in let.

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The "binding" side of a let expression may only have symbols and destructuring forms, such as vectors and maps. The binding side of let can't evaluate an expression like (apply struct storeinfo).

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