Expressions

Expressions

Lisp code is entirely composed of expressions. This means every import, variable declaration, function definition, and if statement evaluates to a value. Expressions are written using either axioms (simple elements, like value literals) or lists, which represent function calls.

Here are some examples of expressions that evaluate to true:

# logic operators are written like function calls.
# While this is confusing at first, this gives every construct the same syntax and helps to mainstream the structure of code
(and (not (<= 1 2)) true)
(= nil (define x 5))
(if (= x 5)  # if is also written with parenthesis
  true
  false)
(= if if)  # if is a first-class citizen
(= () nil)  # nil is the empty list
(= 'x (quote x))  # ' is just a shortcut for (quote)
(or true (do-heavy-stuff))  # or does not evaluate beyond the first true value
# if is a function, although it works differently and can choose how to evaluate its arguments:
(is-instance if function)
(= -14 (+ 1 2 (- 3 (* 4 5))))