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@node Grammar and Parser
@appendix Grammar and Parser
@cindex grammar rules
@cindex language definition

This appendix will eventually contain a semi-formal description of
Octave's language.

@menu
* Keywords::
* Parser::
@end menu

@node Keywords
@section Keywords
@cindex keywords

The identifiers below are keywords, and may not be used as variable
or function names:

@subsubheading Categories:

@ref{XREFkwcategoryUtilityFunctions,,@w{Utility Functions}}@: |
@ref{XREFkwcategoryVariableDeclaration,,@w{Variable Declaration}}@: |
@ref{XREFkwcategoryFunctionDefinition,,@w{Function Definition}}@: |
@ref{XREFkwcategoryControlStructures,,@w{Control Statements}}@: |
@ref{XREFkwcategoryIteratingStructures,,@w{Iterating Structures}}@: |
@ref{XREFkwcategoryClassdefStructures,,@w{Classdef Structures}}@: |
@ref{XREFkwcategoryExecutionEnvironment,,@w{Execution Environment}}@:

@subsubheading Alphabetical keyword listing:

@ref{XREF__FILE__,,__FILE__}@: |
@ref{XREF__LINE__,,__LINE__}@: |
@ref{XREFbreak,,break}@: |
@ref{XREFcase,,case}@: |
@ref{XREFcatch,,catch}@: |
@ref{XREFclassdef,,classdef}@: |
@ref{XREFcontinue,,continue}@: |
@ref{XREFdo,,do}@: |
@ref{XREFelse,,else}@: |
@ref{XREFelseif,,elseif}@: |
@ref{XREFend,,end}@: |
@ref{XREFend_try_catch,,end_try_catch}@: |
@ref{XREFend_unwind_protect,,end_unwind_protect}@: |
@ref{XREFendclassdef,,endclassdef}@: |
@ref{XREFendenumeration,,endenumeration}@: |
@ref{XREFendevents,,endevents}@: |
@ref{XREFendfor,,endfor}@: |
@ref{XREFendfunction,,endfunction}@: |
@ref{XREFendif,,endif}@: |
@ref{XREFendmethods,,endmethods}@: |
@ref{XREFendparfor,,endparfor}@: |
@ref{XREFendproperties,,endproperties}@: |
@ref{XREFendswitch,,endswitch}@: |
@ref{XREFendwhile,,endwhile}@: |
@ref{XREFenumeration,,endenumeration}@: |
@ref{XREFevents,,events}@: |
@ref{XREFfor,,for}@: |
@ref{XREFfunction,,function}@: |
@ref{XREFglobal,,global}@: |
@ref{XREFif,,if}@: |
@ref{XREFkwpropertymethods,,methods}@: |
@ref{XREFotherwise,,otherwise}@: |
@ref{XREFparfor,,parfor}@: |
@ref{XREFpersistent,,persistent}@: |
@ref{XREFkwpropertyproperties,,properties}@: |
@ref{XREFreturn,,return}@: |
@ref{XREFswitch,,switch}@: |
@ref{XREFtry,,try}@: |
@ref{XREFuntil,,until}@: |
@ref{XREFunwind_protect,,unwind_protect}@: |
@ref{XREFunwind_protect_cleanup,,unwind_protect_cleanup}@: |
@ref{XREFwhile,,while}@:

@anchor{XREFkwcategoryUtilityFunctions}
@subheading Utility Functions:
The function @code{iskeyword} can be used to quickly check whether an
identifier is reserved by Octave.

@DOCSTRING(iskeyword)

@anchor{XREFkwcategoryVariableDeclaration}
@subheading Variable Declaration:

@DOCSTRING(global)

@DOCSTRING(persistent)

@anchor{XREFkwcategoryFunctionDefinition}
@subheading Function Definition:

@DOCSTRING(function)

@DOCSTRING(endfunction)

@DOCSTRING(end)

@DOCSTRING(return)

@anchor{XREFkwcategoryControlStructures}
@subheading Control Statements:

@DOCSTRING(if)

@DOCSTRING(else)

@DOCSTRING(elseif)

@DOCSTRING(endif)

@DOCSTRING(switch)

@DOCSTRING(case)

@DOCSTRING(otherwise)

@DOCSTRING(endswitch)

@DOCSTRING(try)

@DOCSTRING(catch)

@DOCSTRING(end_try_catch)

@DOCSTRING(unwind_protect)

@DOCSTRING(unwind_protect_cleanup)

@DOCSTRING(end_unwind_protect)

@anchor{XREFkwcategoryIteratingStructures}
@subheading Iterating Structures:

@DOCSTRING(for)

@DOCSTRING(endfor)

@DOCSTRING(while)

@DOCSTRING(endwhile)

@DOCSTRING(do)

@DOCSTRING(until)

@DOCSTRING(parfor)

@DOCSTRING(endparfor)

@DOCSTRING(break)

@DOCSTRING(continue)

@anchor{XREFkwcategoryClassdefStructures}
@subheading Classdef Structures:

@DOCSTRING(classdef)

@DOCSTRING(endclassdef)

@c properties definition must be manually created to avoid
@c collision with function of the same name.
@anchor{XREFkwpropertyproperties}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html

@deftypefn {} {} properties
Mark the beginning of a block of properties in a classdef definition.  Note
that the @ref{XREFproperties,,function @qcode{"properties"}} is a function
that lists the properties of a classdef class or object.
@seealso{@ref{XREFendproperties,,endproperties}}
@end deftypefn

@DOCSTRING(endproperties)

@c methods definition must be manually created to avoid
@c collision with function of the same name.
@anchor{XREFkwpropertymethods}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html

@deftypefn {} {} methods
Mark the beginning of a block of methods in a classdef definition.  Note that
the @ref{XREFmethods,,function @qcode{"methods"}} is a function that lists
the methods of a class or object.
@seealso{@ref{XREFendmethods,,endmethods}}
@end deftypefn

@DOCSTRING(endmethods)

@DOCSTRING(events)

@DOCSTRING(endevents)

@DOCSTRING(enumeration)

@DOCSTRING(endenumeration)

@anchor{XREFkwcategoryExecutionEnvironment}
@subheading Execution Environment:

@DOCSTRING(__FILE__)

@DOCSTRING(__LINE__)

@node Parser
@section Parser
@cindex parser

The parser has a number of variables that affect its internal operation.
These variables are generally documented in the manual alongside the code that
they affect.

In addition, there are three non-specific parser customization functions.
@code{add_input_event_hook} can be used to schedule a user function for
periodic evaluation.  @code{remove_input_event_hook} will stop a user function
from being evaluated periodically.

@DOCSTRING(add_input_event_hook)

@DOCSTRING(remove_input_event_hook)

Finally, when the parser cannot identify an input token it calls a particular
function to handle this.  By default, this is the internal function
@qcode{"__unimplemented__"} which makes suggestions about possible Octave
substitutes for @sc{matlab} functions.

@DOCSTRING(missing_function_hook)
