Table of Contents

1. If statement in elisp
   1. To remember
      1. Consider the following examples:

TODO If statement in elisp

To remember

According to emacs manual if statement has the following form:

(if nil
    (print 'true)
  'very-false)
⇒ very-false

It is important to remember that this statement has the form: if condition then-form else-forms ... i.e. if condition is fulfilled then-form is evaluated, otherwise the rest of the lines inside external parenthesis.

This means that:

• if you have more than one commands to evaluate in case

condition is fulfilled they need to be embraced by parenthesis and add a special keyword progn (see Sequencing in emacs manual)!!!

• if you have more more than one commands to evaluate in case

condition is not fulfilled they shouldn’t be embraced by parenthesis, because otherwise they are treated as a function! According to emacs manual: ‘‘The else part of if is an example of an implicit progn. See Sequencing.’’

Consider the following examples:

1. Working as intended

   (if t
       (progn
        (print "TRUE: The condition ...")
        (print "... is fulfilled")
       )
        (print "FALSE: The condition ...")
        (print "... is not fulfilled")      
   )
   
   (if nil
       (progn
        (print "TRUE: The condition ...")
        (print "... is fulfilled")
       )
        (print "FALSE: The condition ...")
        (print "... is not fulfilled")      
   )
   

2. Unexpected behaviour

   (if nil
        (print "TRUE: The condition ...")
        (print "... is fulfilled")
        (print "FALSE: The condition ...")
        (print "... is not fulfilled")      
   )
   
   (if t
        (print "TRUE: The condition ...")
        (print "... is fulfilled")
        (print "FALSE: The condition ...")
        (print "... is not fulfilled")      
   )