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A key concept in Scheme is that code is represented the same way as data and that data can be evaluated as code (this property is called homoiconicity, and is a large part of the language's expressive power). When a Scheme interpreter reads a list, it tries to interpret the first value in the list as a function call. For example,
(list 1 2)
is interpreted as a call to the built-in function '(list)', which reads two or more atoms and returns a list. The function would return
(1 2)
as its evaluation.
With a handful of exceptions, all Scheme operations are performed in the form of a function call. For example, to add 2 to 3, you would write:
(+ 2 3)
An extended equation would be written as nested calls:
(/ (- 3 #i3.14) (* (+ 1000 56) 5))
Since Scheme code is freeform, it can be written in a more readable manner like this:
(/ (- 3 #i3.14)
(* (+ 1000 56)
5))