README.nested-if

Nested If Patch
===============

    Allow complex nested conditions in format strings

Patch
-----

    To check if Mutt supports "Nested If", look for "patch-nested-if" in the
    mutt version.

    Dependencies
    * mutt-1.5.24

Introduction
------------

    Mutt's format strings can contain embedded if-then-else conditions. They
    are of the form:

        %?VAR?TRUE&FALSE?

    If the variable "VAR" has a value greater than zero, print the "TRUE"
    string, otherwise print the "FALSE" string.

    e.g. '%?S?Size: %S&Empty?'

    Which can be read as:

        if (%S > 0) {
            print "Size: %S"
        } else {
            print "Empty"
        }


    These conditions are useful, but in Mutt they cannot be nested within one
    another. This patch uses the notation '%<VAR?TRUE&FALSE>' and allows them
    to be nested.

    The '%<...>' notation was used to format the current local time. but that's
    not really very useful since mutt has no means of refreshing the screen
    periodically.

    A simple nested condition might be: (Some whitespace has been introduced
    for clarity)

        %<x? %<y? XY & X > & %<y? Y & NONE > >  Conditions
             %<y? XY & X >                      x>0
                  XY                            x>0,y>0
                       X                        x>0,y=0


        %<x? %<y? XY & X > & %<y? Y & NONE > >  Conditions
                             %<y? Y & NONE >    x=0
                                  Y             x=0,y>0
                                      NONE      x=0,y=0


    Equivalent to:

        if (x > 0) {
            if (y > 0) {
                print 'XY'
            } else {
                print 'X'
            }
        } else {
            if (y > 0) {
                print 'Y'
            } else {
                print 'NONE'
            }
        }


    Examples:

        set index_format='%4C %Z %{%b %d} %-25.25n %s%> %<M?%M Msgs &%<l?%l Lines&%c Bytes>>'

        if a thread is folded
            display the number of messages (%M)
        else if we know how many lines in the message
            display lines in message (%l)
        else
            display the size of the message in bytes (%c)


        set index_format='%4C %Z %{%b %d} %-25.25n %<M?[%M] %s&%s%* %<l?%l&%c>>'

        if a thread is folded
            display the number of messages (%M)
            display the subject (%s)
        else if we know how many lines in the message
            display lines in message (%l)
        else
            display the size of the message in bytes (%c)


Variables
---------

    The nested-if patch doesn't have any config of its own. It modifies the behavior of the
    format strings.

See Also
--------

    * NeoMutt project
    * cond-date patch
    * $index_format
    * $status_format

Known Bugs
----------

    Patch overwrites $<fmt> handler in
    $index_format

Credits
-------

    * David Champion <dgc@uchicago.edu>
    * Richard Russon <rich@flatcap.org>