clojure if-then-else?

Question

This should be a very trivial question. i am new to Clojure and writing this if-then-else based on: http://clojure.org/special_forms#Special%20Forms--%28if%20test%20then%20else?%29

However, I keep getting this error:

java.lang.Exception: Too many arguments to if (NO_SOURCE_FILE:424)

// This code has infinite recursion bugs; but it should compile!
(defn sumdown [sum x]
    (
    if (foo x) 
     (do
     (recur (+ sum x) (dec x))
     )
     else do(
        (recur (+ sum x) (dec x))
     )

     )
) 

Answer 1

In the template:

(if test then else?)

both then and else don't represent keywords, but actual expressions. The ? indicates the else expression is optional.

The test condition is evaluated and based on its value, the appropriate branch expression is evaluated and "returned" as the value of the entire if expression.

For example, this would define an absolute value function:

(defn abs [x]
  (if (< x 0)
    (- x)
    x))

Answer 2

(defn sumdown [sum x]
  (if (foo x)
    (recur (+ sum x) (dec x))
    (recur (+ sum x) (dec x))))

This is the idiomatic way to write this code. I recommend a text editor / IDE with basic support for editing Lisp source (paren/bracket/brace matching).