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System Macros/Action Processing (view source)
Revision as of 09:24, 1 August 2006
, 09:24, 1 August 2006split off section
[[System_Macros]]
ConTeXt makes extensive use of a sort of case or switch command. Depending of the presence of one or more provided items, some actions is taken. These macros can be nested without problems.
<texcode>
\processaction [x] [a=>\a,b=>\b,c=>\c]
\processfirstactioninset [x,y,z] [a=>\a,b=>\b,c=>\c]
\processallactionsinset [x,y,z] [a=>\a,b=>\b,c=>\c]
</texcode>
This macro is most often used in the <code>key-value</code> parser, like in this (simplified) example, where the user has said width=small or something similar:
<texcode>
\processaction
[\TESTwidth] % should expand to 'small'
[small=>\message{small was chosen},
medium=>\message{medium was chosen}]
</texcode>
You can supply both a <code>default</code> action and an action to be undertaken when an <code>unknown</code> value is met:
<texcode>
\processallactionsinset
[x,y,z]
[a=>\a,
b=>\b,
c=>\c,
default=>\default,
unknown=>\unknown{... \commalistelement ...}]
</texcode>
If the first argument is empty, this macro scans the list for the keyword <code>default</code> and executes the related action, if present. If the first argument is not empty but also not in the list, the action related to <code>unknown</code> is executed. Both keywords must be at the end of list <code>#2</code>. Afterwards, the actually found keyword is available in <code>\commalistelement</code>.
Sometimes an action needs to be undertaken that depends only on the first character of something (for instance, checking if some string represents a number or not). This macro get this character and puts it in <code>\firstcharacter</code>.
<texcode>
\getfirstcharacter {string}
</texcode>
ConTeXt makes extensive use of a sort of case or switch command. Depending of the presence of one or more provided items, some actions is taken. These macros can be nested without problems.
<texcode>
\processaction [x] [a=>\a,b=>\b,c=>\c]
\processfirstactioninset [x,y,z] [a=>\a,b=>\b,c=>\c]
\processallactionsinset [x,y,z] [a=>\a,b=>\b,c=>\c]
</texcode>
This macro is most often used in the <code>key-value</code> parser, like in this (simplified) example, where the user has said width=small or something similar:
<texcode>
\processaction
[\TESTwidth] % should expand to 'small'
[small=>\message{small was chosen},
medium=>\message{medium was chosen}]
</texcode>
You can supply both a <code>default</code> action and an action to be undertaken when an <code>unknown</code> value is met:
<texcode>
\processallactionsinset
[x,y,z]
[a=>\a,
b=>\b,
c=>\c,
default=>\default,
unknown=>\unknown{... \commalistelement ...}]
</texcode>
If the first argument is empty, this macro scans the list for the keyword <code>default</code> and executes the related action, if present. If the first argument is not empty but also not in the list, the action related to <code>unknown</code> is executed. Both keywords must be at the end of list <code>#2</code>. Afterwards, the actually found keyword is available in <code>\commalistelement</code>.
Sometimes an action needs to be undertaken that depends only on the first character of something (for instance, checking if some string represents a number or not). This macro get this character and puts it in <code>\firstcharacter</code>.
<texcode>
\getfirstcharacter {string}
</texcode>
