mirror of https://github.com/texmacs/doc.git
165 lines
6.0 KiB
Tcl
165 lines
6.0 KiB
Tcl
<TeXmacs|1.0.7.15>
|
|
|
|
<style|tmdoc>
|
|
|
|
<\body>
|
|
<tmdoc-title|Function definition and contextual overloading>
|
|
|
|
Conventional programming languages often provide mechanism to overload
|
|
certain functions depending on the types of the arguments. <TeXmacs>
|
|
provides additional context-based overloading mechanisms, which require the
|
|
use of the <scm|tm-define> construct for function declarations (and
|
|
<scm|tm-define-macro> for macro declarations). Furthermore, one may use
|
|
<scm|tm-define> for associating additional properties to a function, such
|
|
as documentation or default values for the arguments.
|
|
|
|
<\explain>
|
|
<scm|(tm-define <scm-arg|head> <scm-args|options>
|
|
<scm-args|body>)><explain-synopsis|<TeXmacs> function definition>
|
|
|
|
<scm|(tm-define-macro <scm-arg|head> <scm-args|options>
|
|
<scm-args|body>)><explain-synopsis|<TeXmacs> macro definition>
|
|
<|explain>
|
|
<TeXmacs> function and macro declarations are similar to usual
|
|
declarations based on <scm|define> and <scm|define-macro>, except for the
|
|
additional list of <scm-arg|options> and the fact that all functions and
|
|
macros defined using <scm|tm-define> and <scm|tm-define-macro> are
|
|
public. Each option is of the form <scm|(:<scm-arg|kind>
|
|
<scm-args|arguments>)> and the <scm-arg|body> starts at the first element
|
|
of the list following <scm-arg|head> which is not of this form.
|
|
</explain>
|
|
|
|
<paragraph*|Contextual overloading>
|
|
|
|
We will first describe the most important <scm|:require> option for
|
|
contextual overloading, which was already discussed
|
|
<hlink|before|../overview/overview-overloading.en.tm>.
|
|
|
|
<\explain>
|
|
<scm|(:require <scm-arg|cond>)><explain-synopsis|argument based
|
|
overloading>
|
|
<|explain>
|
|
This option specifies that one necessary condition for the declaration to
|
|
be valid is that the condition <scm-arg|cond> is met. This condition may
|
|
involve the arguments of the function.
|
|
|
|
As an example, let us consider the following definitions:
|
|
|
|
<\scm-code>
|
|
(tm-define (special t)
|
|
|
|
\ \ (and-with p (tree-outer t)
|
|
|
|
\ \ \ \ (special p)))
|
|
|
|
\;
|
|
|
|
(tm-define (special)
|
|
|
|
\ \ (:require (tree-is? t 'frac))
|
|
|
|
\ \ (tree-set! t `(frac ,(tree-ref t 1) ,(tree-ref t 0))))
|
|
|
|
\;
|
|
|
|
(tm-define (special)
|
|
|
|
\ \ (:require (tree-is? t 'rsub))
|
|
|
|
\ \ (tree-set! t `(rsup ,(tree-ref t 0))))
|
|
</scm-code>
|
|
|
|
The default implementation of <scm|special> is to apply <scm|special> to
|
|
the parent <scm|p> of <scm|t> as long as <scm|t> is not the entire
|
|
document itself. The two overloaded cases apply when <scm|t> is either a
|
|
fraction or a right subscript.
|
|
|
|
Assuming that your cursor is inside a fraction inside a subscript,
|
|
calling <scm|special> will swap the numerator and the denominator. On the
|
|
other hand, if your cursor is inside a subscript inside a fraction, then
|
|
calling <scm|special> will change the subscript into a superscript.
|
|
|
|
When the conditions of several (re)declarations are met, then the last
|
|
redeclaration will be used. Inside a redeclaration, one may also use the
|
|
<scm|former> keyword in order to explicitly access the former value of
|
|
the redefined symbol.
|
|
|
|
<\explain>
|
|
<scm|(:mode <scm-arg|mode>)><explain-synopsis|mode-based overloading>
|
|
<|explain>
|
|
This option is equivalent to <scm|(:require (<scm-arg|mode>))> and
|
|
specifies that the definition is only valid when we are in a given
|
|
<scm-arg|mode>. New modes are defined using <scm|texmacs-modes> and
|
|
modes can inherit from other modes.
|
|
</explain>
|
|
</explain>
|
|
|
|
<paragraph*|Other options for function and macro declarations>
|
|
|
|
Besides the contextual overloading options, the <scm|tm-define> and
|
|
<scm|tm-define-macro> primitives admit several other options for attaching
|
|
additional information to the function or macro. We will now describe these
|
|
options and explain how the additional information attached to functions
|
|
can be exploited.
|
|
|
|
<\warning>
|
|
A current limitation of the implementation is that functions overloaded
|
|
using <scm|:require> and <scm|:mode> cannot have different options. This
|
|
means in particular that you cannot specify different values for
|
|
<scm|:synopsis> depending on the context.
|
|
</warning>
|
|
|
|
<\explain>
|
|
<scm|(:synopsis <scm-arg|short-help>)><explain-synopsis|short
|
|
description>
|
|
<|explain>
|
|
This option gives a short discription of the function or macro, in the
|
|
form of a string <scm-arg|short-help>. As a convention, <scheme>
|
|
expressions may be encoded inside this string by using the
|
|
<verbatim|@>-prefix. For instance:
|
|
|
|
<\scm-code>
|
|
(tm-define (list-square l)
|
|
|
|
\ \ (:synopsis "Appends the list @l to itself")
|
|
|
|
\ \ (append l l))
|
|
</scm-code>
|
|
|
|
The synopsis of a function is used for instance in order to provide a
|
|
short help string for the function. In the future, we might also use it
|
|
for help balloons describing menu items.
|
|
</explain>
|
|
|
|
<\explain>
|
|
<scm|(:argument <scm-arg|var> <scm-arg|description>)><explain-synopsis|argument
|
|
description>
|
|
<|explain>
|
|
This option gives a short <scm-arg|description> of one of the arguments
|
|
<scm-arg|var> to the function or macro. Such a description is used for
|
|
instance for the prompts, when calling the function interactively.
|
|
</explain>
|
|
|
|
<\explain>
|
|
<scm|(:returns <scm-arg|description>)><explain-synopsis|return value
|
|
description>
|
|
<|explain>
|
|
This option gives a short <scm-arg|description> of the return value of
|
|
the function or macro.
|
|
</explain>
|
|
|
|
<tmdoc-copyright|2007--2010|Joris van der Hoeven>
|
|
|
|
<tmdoc-license|Permission is granted to copy, distribute and/or modify this
|
|
document under the terms of the GNU Free Documentation License, Version 1.1
|
|
or any later version published by the Free Software Foundation; with no
|
|
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
|
|
Texts. A copy of the license is included in the section entitled "GNU Free
|
|
Documentation License".>
|
|
</body>
|
|
|
|
<\initial>
|
|
<\collection>
|
|
<associate|language|english>
|
|
</collection>
|
|
</initial> |