mirror of https://github.com/texmacs/doc.git
220 lines
8.4 KiB
Tcl
220 lines
8.4 KiB
Tcl
<TeXmacs|1.99.8>
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<style|<tuple|tmdoc|english|old-spacing>>
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<\body>
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<tmdoc-title|Function definition and contextual overloading>
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Conventional programming languages often provide some means to overload
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certain functions depending on the types of the arguments. <TeXmacs>
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provides additional context-based overloading mechanisms, which require the
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use of the <scm|tm-define> construct for function definitions (and
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<scm|tm-define-macro> for macro definitions). Definition with
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<scm|tm-define> also allows the specification of properties of the
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function/macro: arguments, synopsis, etc.
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Furthermore, one may use <scm|tm-property> for associating additional
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properties, such as interactivity or default values for the arguments, of a
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function <em|which is already defined>, specifically functions exported
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from <c++> code through the glue.
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<\explain>
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<scm|(tm-define <scm-arg|head> <scm-args|options>
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<scm-args|body>)><explain-synopsis|<TeXmacs> function definition>
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<scm|(tm-define-macro <scm-arg|head> <scm-args|options>
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<scm-args|body>)><explain-synopsis|<TeXmacs> macro definition>
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<|explain>
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<TeXmacs> function and macro declarations are similar to usual
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declarations based on <scm|define> and <scm|define-macro>, except for the
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additional list of <scm-arg|options> and the fact that all functions and
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macros defined using <scm|tm-define> and <scm|tm-define-macro> are
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public. Each option is of the form <scm|(:<scm-arg|kind>
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<scm-args|arguments>)> and the <scm-arg|body> starts at the first element
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of the list following <scm-arg|head> which is not of this form. Available
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options are <scm|:type>, <scm|:synopsis>, <scm|:returns>, <scm|:note>,
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<scm|:argument>, <scm|:default>, <scm|:proposals>, <scm|:secure>,
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<scm|:check-mark>, <scm|:interactive> and <scm|:balloon>.
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</explain>
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<\explain>
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<scm|(tm-property <scm-arg|head> <scm-args|options>)><explain-synopsis|<TeXmacs>
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properties definition>
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<|explain>
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<scm|tm-property> allows the declaration of <TeXmacs> properties for
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functions which have already been defined, specifically for functions
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exported through the glue. Available options are <scm|:type>,
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<scm|:synopsis>, <scm|:returns>, <scm|:note>, <scm|:argument>,
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<scm|:default>, <scm|:proposals>, <scm|:secure>, <scm|:check-mark>,
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<scm|:interactive> and <scm|:balloon>.
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</explain>
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<paragraph*|Contextual overloading>
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We will first describe the most important <scm|:require> option for
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contextual overloading, which was already discussed
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<hlink|before|../overview/overview-overloading.en.tm>.
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<\explain>
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<scm|(:require <scm-arg|cond>)><explain-synopsis|argument based
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overloading>
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<|explain>
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This option specifies that one necessary condition for the declaration to
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be valid is that the condition <scm-arg|cond> is met. This condition may
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involve the arguments of the function.
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As an example, let us consider the following definitions:
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<\scm-code>
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(tm-define (special t)
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\ \ (and-with p (tree-outer t)
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\ \ \ \ (special p)))
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\;
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(tm-define (special)
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\ \ (:require (tree-is? t 'frac))
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\ \ (tree-set! t `(frac ,(tree-ref t 1) ,(tree-ref t 0))))
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\;
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(tm-define (special)
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\ \ (:require (tree-is? t 'rsub))
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\ \ (tree-set! t `(rsup ,(tree-ref t 0))))
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</scm-code>
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The default implementation of <scm|special> is to apply <scm|special> to
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the parent <scm|p> of <scm|t> as long as <scm|t> is not the entire
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document itself. The two overloaded cases apply when <scm|t> is either a
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fraction or a right subscript.
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Assuming that your cursor is inside a fraction inside a subscript,
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calling <scm|special> will swap the numerator and the denominator. On the
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other hand, if your cursor is inside a subscript inside a fraction, then
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calling <scm|special> will change the subscript into a superscript.
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When the conditions of several (re)declarations are met, then the last
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redeclaration will be used. Inside a redeclaration, one may also use the
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<scm|former> keyword in order to explicitly access the former value of
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the redefined symbol.
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</explain>
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<\explain>
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<scm|(:mode <scm-arg|mode>)><explain-synopsis|mode-based overloading>
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<|explain>
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This option is equivalent to <scm|(:require (<scm-arg|mode>))> and
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specifies that the definition is only valid when we are in a given
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<scm-arg|mode>. New modes are defined using <scm|texmacs-modes> and modes
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can inherit from other modes.
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</explain>
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<\explain>
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<scm|(texmacs-modes . <scm-arg|modedefs>)> <explain-synopsis|define new
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texmacs modes>
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<|explain>
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Use this macro to define new modes that you can use for contextual
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overloading, for instance in <scm|kbd-map>. Modes may be made dependent
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on other modes. This macro takes a variable number of definitions as
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arguments, each of the form <scm|(mode-name conditions . dependencies)>.
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End your <scm|mode-name> and any dependencies with one <scm|%>, like
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this:
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<\scm-code>
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(texmacs-modes
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\ \ (in-verbatim% (inside? 'verbatim) in-text%)
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\ \ (in-tt% (inside? 'tt)))
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</scm-code>
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When creating new modes remember to place first the faster checks
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(against booleans, etc.) for speed.
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</explain>
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<paragraph*|Other options for function and macro declarations>
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Besides the contextual overloading options, the <scm|tm-define> and
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<scm|tm-define-macro> primitives admit several other options for attaching
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additional information to the function or macro. We will now describe these
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options and explain how the additional information attached to functions
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can be exploited.
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<\warning>
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A current limitation of the implementation is that functions overloaded
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using <scm|:require> and <scm|:mode> cannot have different options. This
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means in particular that you cannot specify different values for
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<scm|:synopsis> depending on the context.
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</warning>
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<\explain>
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<scm|(:synopsis <scm-arg|short-help>)><explain-synopsis|short
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description>
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<|explain>
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This option gives a short description of the function or macro, in the
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form of a string <scm-arg|short-help>. As a convention, <scheme>
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expressions may be encoded inside this string by using the
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<verbatim|@>-prefix. For instance:
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<\scm-code>
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(tm-define (list-square l)
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\ \ (:synopsis "Appends the list @l to itself")
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\ \ (append l l))
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</scm-code>
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The synopsis of a function is used for instance in order to provide a
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short help string for the function. In the future, we might also use it
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for help balloons describing menu items.
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</explain>
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<\explain>
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<scm|(:argument <scm-arg|var> <scm-arg|description>)>
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<scm|(:argument <scm-arg|var> <scm-arg|type>
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<scm-arg|description>)><explain-synopsis|argument description>
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<|explain>
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This option gives a short <scm-arg|description> of one of the arguments
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<scm-arg|var> to the function or macro. Such a description is used for
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instance for the prompts, when calling the function interactively. For
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these uses, the second format allows for the specification of a
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<scm-arg|type> which changes how the widgets/prompts work. Some allowed
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values are <scm|"string">, the default, and <scm|"file"> and
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<scm|"directory">. If any of the last two is specified, tab completion in
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the interactive prompt will traverse the file system.
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</explain>
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<\explain>
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<scm|(:returns <scm-arg|description>)><explain-synopsis|return value
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description>
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<|explain>
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This option gives a short <scm-arg|description> of the return value of
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the function or macro.
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</explain>
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<\explain>
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<scm|(:type (-\<gtr\> <scm-arg|from> <scm-arg|to>))><explain-synopsis|type
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conversion description>
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<|explain>
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This option specifies that a function or macro performs a conversion from
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the data type <scm-arg|from> to the data type <scm-arg|to>.
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</explain>
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<tmdoc-copyright|2007--2010|Joris van der Hoeven>
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<tmdoc-license|Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version 1.1
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or any later version published by the Free Software Foundation; with no
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Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled "GNU Free
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Documentation License".>
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</body>
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<initial|<\collection>
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</collection>> |