Quick Review 1¶

Expressions¶

ClojureScript programs consist of expressions. An expression is made up of an open parenthesis, a function name, the function’s arguments, and a closing parenthesis. You may nest expressions as deeply as you wish, though the more deeply you nest them, the harder your code may be to read and understand.

Examples:

• (+ 3 5)
• (* 3 (+ 4 5))
• (/ (+ 3 4) (* (- 5 6) (+ 7 8)))

Arithmetic Functions¶

Here are the arithmetic functions:

Arithmetic functions other than quot and rem can take more than two arguments:

• (+ 3 4 5) evaluates to 12
• (- 10 3 2) evaluates to 5
• (* 3 4 5 6) evaluates to 360
• (/ 168 3 8 2) evaluates to 3.5

Numbers¶

You can write numbers in many different ways:

• 2 (integer)
• 2.3 (decimal)
• 2.345e02 (scientific notation)
• 0x1af (hexadecimal—base 16 integers)
• 017 (octal—base 8 integers)
• 2r1001 (binary—base 2 integers)

Negative numbers start with a - as the first character.

Octal doesn’t have an identifying letter like hexadecimal, so if you try to write a number like 009, ClojureScript will complain. The last form lets you specify the number base—2 in the example—followed by the letter r, followed by the number. You can explicitly specify an octal integer as 8r017.

Binding Symbols and Values¶

You bind a value and a symbol with def; the general form is

(def symbol value)

Symbols consist of letters, digits, and any of *, +, !, -, _, ‘, and ?—but they cannot begin with a numeric. The value may be an expression and may use previously bound symbols:

(def seconds-per-min 60)
(def min-per-hour 60)
(def seconds-per-hour (* seconds-per-min min-per-hour))

Defining Functions¶

You define functions with defn. The general form for defining a function is:

(defn function-name [parameter1 parameter2 ...]
  (expression))

You can create local bindings within a function with the let construct:

(defn function-name [parameter1 parameter2 ...]
  (let [symbol1 value1
        symbol2 value2
        ...]
    (expression))

The value of the last expression in the function is the value that the function yields.