!if(4)

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NAME

!if, !elif, !else, !endif - Conditional statements

SYNOPSIS

!if condition

... condition body ...

!elif

condition

... condition body ...

!else

... condition body ...

!endif

!iif condition body

DESCRIPTION

The conditional directives allow statements to be executed only if a condition specified in the directive is met, as follows:-

Every line following the !if directive, until the first !elif, !else or !endif directive, is only executed if the expression following the !if directive evaluates to a TRUE value (non-zero).
If the !if evaluates to FALSE and a !elif directive is next then the expression following the !if is evaluated and following statements are executed if TRUE.
If no !if or !elif is found to be TRUE and a !else is found then the statements following it are executed.

The condition may be any logical condition as evaluated by the variable functions (e.g. &equal(4)) returning TRUE or FALSE. An integer value, non-zero evaluates TRUE, zero evaluates to FALSE. A non-numerical argument, such as a string is always FALSE.

The conditional body may be any MicroEmacs function, macro or directive with the exception of define-macro and !emacro. All directives that alter the execution of the macro are handled correctly within the !if statement (e.g. !goto, !return etc).

!iif provides an optimal way to write an !if statement with exactly one body line and no !elif or !else statements.

EXAMPLE

The following macro segment creates the portion of a text file automatically. (yes believe me, this will be easier to understand then that last explanation....)

!if &sequal %curplace "timespace vortex" 
    insert-string "First, rematerialize\n" 
!endif 
!if &sequal %planet "earth"	;If we have landed on earth... 
    !if &sequal %time "late 20th century"  ;and we are then 
        ml-write "Contact U.N.I.T." 
    !elif &sequal %time "pre 20th century" 
        ml-write "start praying for a miracle" 
    !else 
        insert-string "Investigate the situation....\n" 
        insert-string "(SAY 'stay here Sara')\n" 
    !endif 
!else 
    set-variable %conditions @ml"Atmosphere conditions outside? " 
    !if &sequal %conditions "safe" 
        insert-string &cat "Go outside......" "\n" 
        insert-string "lock the door\n" 
    !else 
        insert-string "Dematerialize..try somewhere else" 
        newline 
    !endif 
!endif

The first !if statement in the above example can be optimised to:-

!iif &sequal %curplace "timespace vortex"  insert-string "First, rematerialize\n"

NOTES

There is a convention in MicroEmacs macro code of using 2 spaces to separate the condition from the body of an !iif statement making it easier to locate the start of the body.

!if(4)

NAME

SYNOPSIS

DESCRIPTION

EXAMPLE

NOTES

SEE ALSO