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eintr: if

 
 3.7 The ‘if’ Special Form
 =========================
 
 A 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!”
 

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· if in more detail
· type-of-animal in detail    An example of an ‘if’ expression.
 

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