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 #command | #translate 
 Specify a user-defined command or translation directive

     #command   <matchPattern> => <resultPattern>
     #translate   <matchPattern> => <resultPattern>


     <matchPattern> is the pattern the input text should match.

     <resultPattern> is the text produced if a portion of input text
     matches the <matchPattern>.

     The => symbol between <matchPattern> and <resultPattern> is, along with
     #command or #translate, a literal part of the syntax that must be
     specified in a #command or #translate directive.  The symbol consists of
     an equal sign followed by a greater than symbol with no intervening
     spaces.  Do not confuse the symbol with the >= or the <= comparison
     operators in the CA-Clipper language.


     #command and #translate are translation directives that define commands
     and pseudofunctions.  Each directive specifies a translation rule.  The
     rule consists of two portions:  a match pattern and a result pattern.
     The match pattern matches a command specified in the program (.prg) file
     and saves portions of the command text (usually command arguments) for
     the result pattern to use.  The result pattern then defines what will be
     written to the result text and how it will be written using the saved
     portions of the matching input text.

     #command and #translate are similar, but differ in the circumstance
     under which their match patterns match input text.  A #command directive
     matches only if the input text is a complete statement, while #translate
     matches input text that is not a complete statement.  #command defines a
     complete command and #translate defines clauses and pseudofunctions that
     may not form a complete statement.  In general, use #command for most
     definitions and #translate for special cases.

     #command and #translate are similar to but more powerful than the
     #define directive.  #define, generally, defines identifiers that control
     conditional compilation and manifest constants for commonly used
     constant values such as INKEY() codes.  Refer to any of the header files
     in the \CLIP53\INCLUDE directory for examples of manifest constants
     defined using #define.

     #command and #translate directives have the same scope as the #define
     directive.  The definition is valid only for the current program (.prg)
     file unless defined in Std.ch or the header specified with the /U option
     on the compiler command line.  If defined elsewhere, the definition is
     valid from the line where it is specified to the end of the program
     file.  Unlike #define, a #translate or #command definition cannot be
     explicitly undefined.  The #undef directive has no effect on a #command
     or #translate definition.

     As the preprocessor encounters each source line preprocessor, it scans
     for definitions in the following order of precedence: #define,
     #translate, and #command.  When there is a match, the substitution is
     made to the result text and the entire line is reprocessed until there
     are no matches for any of the three types of definitions.  #command and
     #translate rules are processed in stack-order (i.e., last in-first out,
     with the most recently specified rule processed first).

     In general, a command definition provides a way to specify an English
     language statement that is, in fact, a complicated expression or
     function call, thereby improving the readability of source code.  You
     can use a command in place of an expression or function call to impose
     order of keywords, required arguments, combinations of arguments that
     must be specified together, and mutually exclusive arguments at compile
     time rather than at runtime.  This can be important since procedures and
     user-defined functions can now be called with any number of arguments,
     forcing any argument checking to occur at runtime.  With command
     definitions, the preprocessor handles some of this.

     All commands in CA-Clipper are defined using the #command directive and
     supplied in the standard header file, Std.ch, located in the
     \CLIP53\INCLUDE directory.  The syntax rules of #command and #translate
     facilitate the processing of all CA-Clipper and dBASE-style commands
     into expressions and function calls.  This provides CA-Clipper
     compatibility, as well as avenues of compatibility with other dialects.

     When defining a command, there are several prerequisites to properly
     specifying the command definition.  Many preprocessor commands require
     more than one #command directive because mutually exclusive clauses
     contain a keyword or argument.  For example, the @...GET command has
     mutually exclusive VALID and RANGE clauses and is defined with a
     different #command rule to implement each clause.

     This also occurs when a result pattern contains different expressions,
     functions, or parameter structures for different clauses specified for
     the same command (e.g., the @...SAY command).  In Std.ch, there is a
     #command rule for @...SAY specified with the PICTURE clause and another
     for @...SAY specified without the PICTURE clause.  Each formulation of
     the command is translated into a different expression.  Because
     directives are processed in stack order, when defining more than one
     rule for a command, place the most general case first, followed by the
     more specific ones.  This ensures that the proper rule will match the
     command specified in the program (.prg) file.

     For more information and a general discussion of commands, refer to the
     "Basic Concepts" chapter in the Programming and Utilities Guide.

 Match Pattern

     The <matchPattern> portion of a translation directive is the pattern the
     input text must match.  A match pattern is made from one or more of the
     following components, which the preprocessor tries to match against
     input text in a specific way:

     .  Literal values are actual characters that appear in the match
        pattern.  These characters must appear in the input text, exactly as
        specified to activate the translation directive.

     .  Words are keywords and valid identifiers that are compared
        according to the dBASE convention (case-insensitive, first four
        letters mandatory, etc.).  The match pattern must start with a Word.

        #xcommand and #xtranslate can recognize keywords of more than four
        significant letters.

     .  Match markers are label and optional symbols delimited by
        angle brackets (<>) that provide a substitute (idMarker) to be used
        in the <resultPattern> and identify the clause for which it is a
        substitute.  Marker names are identifiers and must, therefore, follow
        the CA-Clipper identifier naming conventions.  In short, the name
        must start with an alphabetic or underscore character, which may be
        followed by alphanumeric or underscore characters.

        This table describes all match marker forms:

        Match Markers
        Match Marker             Name
        <idMarker>               Regular match marker
        <idMarker,...>           List match marker
        <idMarker:word list>     Restricted match marker
        <*idMarker*>             Wild match marker
        <(idMarker)>             Extended Expression match marker

        -  Regular match marker: Matches the next legal expression in the
           input text.  The regular match marker, a simple label, is the most
           general and, therefore, the most likely match marker to use for a
           command argument.  Because of its generality, it is used with the
           regular result marker, all of the stringify result markers, and
           the blockify result marker.

        -  List match marker: Matches a comma-separated list of legal
           expressions.  If no input text matches the match marker, the
           specified marker name contains nothing.  You must take care in
           making list specifications because extra commas will cause
           unpredictable and unexpected results.

           The list match marker defines command clauses that have lists as
           arguments.  Typically these are FIELDS clauses or expression lists
           used by database commands.  When there is a match for a list match
           marker, the list is usually written to the result text using either the
           normal or smart stringify result marker.  Often, lists are written
           as literal arrays by enclosing the result marker in curly ({ })

        -  Restricted match marker: Matches input text to one of the
           words in a comma-separated list.  If the input text does not match
           at least one of the words, the match fails and the marker name
           contains nothing.

           A restricted match marker is generally used with the logify result
           marker to write a logical value into the result text.  If there is
           a match for the restricted match marker, the corresponding logify
           result marker writes true (.T.) to the result text; otherwise, it
           writes false (.F.).  This is particularly useful when defining
           optional clauses that consist of a command keyword with no
           accompanying argument.  Std.ch implements the REST clause of
           database commands using this form.

        -  Wild match marker: Matches any input text from the current
           position to the end of a statement.  Wild match markers generally
           match input that may not be a legal expression, such as #command
           NOTE <*x*> in Std.ch, gather the input text to the end of the
           statement, and write it to the result text using one of the
           stringify result markers.

        -  Extended expression match marker: Matches a regular or
           extended expression, including a file name or path specification.
           It is used with the smart stringify result marker to ensure that
           extended expressions will not get stringified, while normal,
           unquoted string file specifications will.

     .  Optional match clauses are portions of the match pattern
        enclosed in square brackets ([ ]).  They specify a portion of the
        match pattern that may be absent from the input text.  An optional
        clause may contain any of the components allowed within a
        <matchPattern>, including other optional clauses.

        Optional match clauses may appear anywhere and in any order in the
        match pattern and still match input text.  Each match clause may
        appear only once in the input text.  There are two types of optional
        match clauses: one is a keyword followed by match marker, and the
        other is a keyword by itself.  These two types of optional match
        clauses can match all of the traditional command clauses typical of
        the CA-Clipper command set.

        Optional match clauses are defined with a regular or list match
        marker to match input text if the clause consists of an argument or a
        keyword followed by an argument (see the INDEX clause of the USE
        command in Std.ch).  If the optional match clause consists of a
        keyword by itself, it is matched with a restricted match marker (see
        the EXCLUSIVE or SHARED clause of the USE command in Std.ch).

        In any match pattern, you may not specify adjacent optional match
        clauses consisting solely of match markers, without generating a
        compiler error.  You may repeat an optional clause any number of
        times in the input text, as long as it is not adjacent to any other
        optional clause.  To write a repeated match clause to the result
        text, use repeating result clauses in the <resultPattern> definition.

See Also: #define #xcommand
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