Wherever an example of evaluating a Lisp form is shown it will be formatted like this,
(+ 1 2) ⇒ 3
The glyph ‘⇒’ is used to show the computed value of a form. 1
When two forms are shown as being exactly equivalent to one another the glyph ‘≡’ is used, for example,
(car some-variable) ≡ (nth 0 some-variable)
Evaluating some forms result in an error being signalled, this is denoted by the ‘error→’ glyph.
(open-file "/tmp/foo" 'read) error→ File error: No such file or directory, /tmp/foo
In this case the list ‘(+ 1 2)’ (i.e. the list
containing three elements, the symbol
+ and, the numbers 1 and
2), represents a function application. The first element in the list is
the name of the function to be called, all other elements are the
arguments to apply to it. Since the
+ function adds a series of
numbers, the above function call is actually performing the computation
‘1 + 2’.