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if
Special FormA third special form, in addition to defun
and let
, is the
conditional if
. This form is used to instruct the computer to
make decisions. You can write function definitions without using
if
, but it is used often enough, and is important enough, to be
included here. It is used, for example, in the code for the
function beginning-of-buffer
.
The basic idea behind an if
, is that if a test is true,
then an expression is evaluated. If the test is not true, the
expression is not evaluated. For example, you might make a decision
such as, “if it is warm and sunny, then go to the beach!”
• if in more detail: | ||
• type-of-animal in detail: | An example of an if expression.
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