( Inhibiting Invocation

Info Catalog ( Invocation ( Macros ( Macro Arguments
 3.2 Preventing macro invocation
 An innovation of the `m4' language, compared to some of its
 predecessors (like Stratchey's `GPM', for example), is the ability to
 recognize macro calls without resorting to any special, prefixed
 invocation character.  While generally useful, this feature might
 sometimes be the source of spurious, unwanted macro calls.  So, GNU
 `m4' offers several mechanisms or techniques for inhibiting the
 recognition of names as macro calls.
    First of all, many builtin macros cannot meaningfully be called
 without arguments.  For any of these macros, whenever an opening
 parenthesis does not immediately follow their name, the builtin macro
 call is not triggered.  This solves the most usual cases, like for
 `include' or `eval'.  Later in this document, the sentence "This macro
 is recognized only with parameters" refers to this specific provision.
    There is also a command line option (`--prefix-builtins', or `-P',
  Invoking m4) that renames all builtin macro with a prefix of
 `m4_' at startup.  The option has no effect whatsoever on user defined
 macros.  For example, with this option, one has to write `m4_dnl' and
 even `m4_m4exit'.  It also has no effect on whether a macro requires
    Another alternative is to redefine problematic macros to a name less
 likely to cause conflicts,  Definitions.
    If your version of GNU `m4' has the `changeword' feature compiled
 in, it offers far more flexibility in specifying the syntax of macro
 names, both builtin or user-defined.   Changeword, for more
 information on this experimental feature.
    Of course, the simplest way to prevent a name from being interpreted
 as a call to an existing macro is to quote it.  The remainder of this
 section studies a little more deeply how quoting affects macro
 invocation, and how quoting can be used to inhibit macro invocation.
    Even if quoting is usually done over the whole macro name, it can
 also be done over only a few characters of this name (provided, of
 course, that the unquoted portions are not also a macro).  It is also
 possible to quote the empty string, but this works only _inside_ the
 name.  For example:
 all yield the string `divert'.  While in both:
 the `divert' builtin macro will be called, which expands to the empty
    The output of macro evaluations is always rescanned.  The following
 example would yield the string `de', exactly as if `m4' has been given
 `substr(`abcde', `3', `2')' as input:
      define(`x', `substr(ab')
      define(`y', `cde, `3', `2')')
    Unquoted strings on either side of a quoted string are subject to
 being recognized as macro names.  In the following example, quoting the
 empty string allows for the second `macro' to be recognized as such:
      define(`macro', `m')
    Quoting may prevent recognizing as a macro name the concatenation of
 a macro expansion with the surrounding characters.  In this example:
      define(`macro', `di$1')
 the input will produce the string `divert'.  When the quotes were
 removed, the `divert' builtin was called instead.
Info Catalog ( Invocation ( Macros ( Macro Arguments
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