How <tt>define-text-object</tt> works

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How define-text-object works

  Lisp macro define-text-object is quite involved. In this overview, we use the call shown in fig:define-kronecker to illustrate the various steps. A call to macro define-text-object performs the following steps:

Define class:
Generate the class definition for the new object type. In our example, it produces:


If the corresponding macro takes [tex2html_wrap5500] arguments, i.e., [tex2html_wrap5502] in fig:define-kronecker, then the new object type is defined to have a slot arguments. This slot will hold a list containing the result of processing the [tex2html_wrap5504] arguments of the La)TeX macro call.

Define processing function:
Define a processing function that is called to process instances of the La)TeX macro call. The function applies the recursive-descent algorithm to the next number-args tokens from the input stream. In the current example, the function generated is:


where variable number-args is bound to the value of the number-args keyword argument in the lexical scope in which the function definition is evaluated. Functions process-argument-as-math and process-argument-as-text apply the recursive descent parser to their argument; the former parses mathematical content, the latter processes plain text.

Define accessor methods:
If [tex2html_wrap5506], accessor method argument is generated. Method argument takes two arguments, an instance [tex2html_wrap5508] of the new object and an integer [tex2html_wrap5510], and retrieves the result of processing argument [tex2html_wrap5512] of the corresponding call to the La)TeX macro. It is used in the rendering rules to retrieve different pieces of a La)TeX macro call. See s:sample-macro-reading for an example of its use. Assuming that [tex2html_wrap5514], this method looks like:


We take advantage of the generic dispatch provided by CLOS and define an instance of the above method with its arguments reversed -this avoids having to remember the order of arguments to function argument when writing rendering rules.

Define precedence:
If the precedence keyword argument is supplied, an appropriate call to define-precedence is generated:


Install macro definition:
Finally, the La)TeX macro is installed in a global table that records all known La)TeX macros.


This specifies that the macro being defined takes [tex2html_wrap5516] arguments and calls to it should be processed using function kronecker-expand.

The call to the Lisp macro define-text-object shown in this example produces [tex2html_wrap5518] lines of Lisp code.

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TV Raman
Thu Mar 9 20:10:41 EST 1995