Difference between revisions of "Commands with KeyVal arguments"

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< [[Inside ConTeXt]]
 
< [[Inside ConTeXt]]
  
−
(a post on the mailing list by Taco Hoekwater from [[http://www.mail-archive.com/ntg-context@ntg.nl/msg03235.html 2004-06-28]]:)
+
This article is based on a post on the mailing list by Taco Hoekwater from [[http://www.mail-archive.com/ntg-context@ntg.nl/msg03235.html 2004-06-28]].
 +
 
 +
== Example code ==
 +
 
 +
<texcode>
 +
\unprotect % enable exclamations in macro names
 +
 
 +
% Helper function: if the user specifies nothing, throw an error
 +
\def\errorDir{%
 +
  \def\Dir{0}% error recovery
 +
  \message{Please supply "Dir" argument}%
 +
}
 +
 
 +
% Helper function: process Dir=... other than Up/Down/Left/Right
 +
% Accept numbers, else throw an error
 +
\def\checkDir#1{%
 +
  \doifnumberelse {#1}
 +
                  {\def\Dir{#1}}
 +
                  {\message{Invalid "Dir" argument! (#1)}}
 +
}
 +
 
 +
% Defining our command that accepts key=val
 +
\def\MyZigzag#1[#2]{%
 +
  % the #1 makes sure we allow a space before the bracket
 +
 
 +
  % create commands \ZZDir, \ZZLinewidth (default 1pt), etc.
 +
  \getparameters[ZZ][Dir=,Linewidth=1pt,Color=Red,Width=3em,#2]
 +
 
 +
  % define an alias
 +
  \edef\mywidth{\ZZWidth}%
 +
 
 +
  % accept keywords for Dir= (and map those keywords to numbers)
 +
  %\expandafter\processaction\expandafter[\ZZDir] % mkii
 +
  \processaction[\ZZDir]                          % mkiv
 +
[      Down=>\def\Dir{270},
 +
      Left=>\def\Dir{180},
 +
          Up=>\def\Dir{90},
 +
      Right=>\def\Dir{0},
 +
\s!default=>\errorDir,
 +
\s!unknown=>\checkDir{\ZZDir}]
 +
} % this brace belongs to \def!
 +
 
 +
\protect % end of definitions
 +
</texcode>
 +
 
 +
== Same example with commentary ==
  
 
The 'key' to the keyval functionality in ConTeXt are two macros called
 
The 'key' to the keyval functionality in ConTeXt are two macros called
 
{{cmd|getparameters}} and {{cmd|processaction}}.
 
{{cmd|getparameters}} and {{cmd|processaction}}.
−
 
−
Here is a 'quickstart', assuming you want to define <tt>\MyZigzag</tt>. The code example is interrupted with explantory running text.
 
  
 
<texcode>
 
<texcode>
Line 28: Line 71:
  
 
<texcode>
 
<texcode>
−
   \expandafter\processaction\expandafter[\ZZDir]
+
   %\expandafter\processaction\expandafter[\ZZDir] % mkii
−
[Down       =>\def\Dir{270},
+
  \processaction[\ZZDir]                          % mkiv
−
Left       =>\def\Dir{180},
+
[     Down=>\def\Dir{270},
−
  Up         =>\def\Dir{90},
+
      Left=>\def\Dir{180},
−
Right     =>\def\Dir{0},
+
          Up=>\def\Dir{90},
−
\s!default =>\errorDir,  
+
      Right=>\def\Dir{0},
−
\s!unknown =>\checkDir{\ZZDir}]
+
\s!default=>\errorDir,  
 +
\s!unknown=>\checkDir{\ZZDir}]
 
} % this brace belongs to \def!
 
} % this brace belongs to \def!
 
</texcode>
 
</texcode>
Line 40: Line 84:
 
<tt>\s!default</tt> may be triggered because <tt>\ZZDir</tt>'s expansion is empty unless the user supplied something.
 
<tt>\s!default</tt> may be triggered because <tt>\ZZDir</tt>'s expansion is empty unless the user supplied something.
  
−
The first argument to {{cmd|processaction}} has to be expanded, so you need the {{cmd|expandafter}}s.
+
In MkII, the first argument to {{cmd|processaction}} has to be expanded, so you need the {{cmd|expandafter}}s. In MkIV, {{cmd|processaction|link=no}} does this automatically.
  
−
for completeness, here is an example definition of <tt>\checkDir</tt> and <tt>\errorDir</tt>:
+
For completeness, here is an example definition of <tt>\checkDir</tt> and <tt>\errorDir</tt>:
  
 
<texcode>
 
<texcode>

Revision as of 09:15, 23 August 2012

< Inside ConTeXt

This article is based on a post on the mailing list by Taco Hoekwater from [2004-06-28].

Example code

\unprotect % enable exclamations in macro names

% Helper function: if the user specifies nothing, throw an error
\def\errorDir{%
   \def\Dir{0}% error recovery
   \message{Please supply "Dir" argument}%
}

% Helper function: process Dir=... other than Up/Down/Left/Right
% Accept numbers, else throw an error
\def\checkDir#1{%
  \doifnumberelse {#1}
                  {\def\Dir{#1}}
                  {\message{Invalid "Dir" argument! (#1)}}
}

% Defining our command that accepts key=val
\def\MyZigzag#1[#2]{%
  % the #1 makes sure we allow a space before the bracket

  % create commands \ZZDir, \ZZLinewidth (default 1pt), etc.
  \getparameters[ZZ][Dir=,Linewidth=1pt,Color=Red,Width=3em,#2]

  % define an alias
  \edef\mywidth{\ZZWidth}%

  % accept keywords for Dir= (and map those keywords to numbers)
  %\expandafter\processaction\expandafter[\ZZDir] % mkii
  \processaction[\ZZDir]                          % mkiv
	[      Down=>\def\Dir{270},
	       Left=>\def\Dir{180},
   	         Up=>\def\Dir{90},
 	      Right=>\def\Dir{0},
	 \s!default=>\errorDir, 
	 \s!unknown=>\checkDir{\ZZDir}]
} % this brace belongs to \def!

\protect % end of definitions

Same example with commentary

The 'key' to the keyval functionality in ConTeXt are two macros called \getparameters and \processaction. 

\unprotect % enable exclamations in macro names

\def\MyZigzag#1[#2]{% % This brace is closed below, after the \expandafter block
  % the #1 makes sure we allow a space before the bracket

  \getparameters[ZZ][Dir=,Linewidth=1pt,Color=Red,Width=3em,#2]

Now you have a set of new macros that all start with ZZ. At least there are \ZZDir,\ZZLinewidth, \ZZColor and \ZZWidth (these have default values) but possibly others as well, depending on user input. In the next lines you make use of these variables, for example as follows: 

 \edef\mywidth{\ZZWidth}%

If you want some of the variables to accept keyword values, then you also need to use \processaction on the ZZ variable in question to map the keywords onto actual values.

Say you want "Dir" to be mandatory and that it accepts 4 directional keywords, as well as a direct angle specification. I've used all mixed case keywords, because otherwise you might run into conflicts with the multilingual interface: 

  %\expandafter\processaction\expandafter[\ZZDir] % mkii
  \processaction[\ZZDir]                          % mkiv
	[      Down=>\def\Dir{270},
	       Left=>\def\Dir{180},
   	         Up=>\def\Dir{90},
 	      Right=>\def\Dir{0},
	 \s!default=>\errorDir, 
	 \s!unknown=>\checkDir{\ZZDir}]
} % this brace belongs to \def!

\s!default may be triggered because \ZZDir's expansion is empty unless the user supplied something.

In MkII, the first argument to \processaction has to be expanded, so you need the \expandafters. In MkIV, \processaction does this automatically.

For completeness, here is an example definition of \checkDir and \errorDir: 

\def\errorDir{%
   \def\Dir{0}% error recovery
   \message{Please supply "Dir" argument}%
}

\def\checkDir#1{%
  \doifnumberelse {#1}
                  {\def\Dir{#1}}
                  {\message{Invalid "Dir" argument! (#1)}}
}

\protect % end of definitions
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