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% These functions were taken from the jed editor
static variable Features = Assoc_Type [Int_Type,0];
%!%+
%\function{_featurep}
%\synopsis{Test whether or not a feature is present}
%\usage{Int_Type _featurep (String_Type feature)}
%\description
% The \sfun{_featurep} function returns a non-zero value if the specified
% feature is present. Otherwise, it returns 0 to indicate that the feature
% has not been loaded.
%\seealso{require, provide}
%!%-
public define _featurep (f)
{
Features[f];
}
%!%+
%\function{provide}
%\synopsis{Declare that a specified feature is available}
%\usage{provide (String_Type feature)}
%\description
% The \sfun{provide} function may be used to declare that a "feature" has
% been loaded. See the documentation for \sfun{require} for more information.
%\seealso{require, _featurep}
%!%-
public define provide (f)
{
Features[f] = 1;
}
%!%+
%\function{require}
%\synopsis{Make sure a feature is present, and load it if not}
%\usage{require (String_Type feature [,String_Type file]}
%\description
% The \sfun{require} function ensures that a specified "feature" is present.
% If the feature is not present, the \sfun{require} function will attempt to
% load the feature from a file. If called with two arguments, the feature
% will be loaded from the file specified by the second argument. Otherwise,
% the feature will be loaded from a file given by the name of the feature,
% with ".sl" appended.
%
% If after loading the file, if the feature is not present,
% a warning message will be issued.
%\notes
% "feature" is an abstract quantity that is undefined here.
%
% A popular use of the \sfun{require} function is to ensure that a specified
% file has already been loaded. In this case, the feature is the
% filename itself. The advantage of using this mechanism over using
% \ifun{evalfile} is that if the file has already been loaded, \sfun{require}
% will not re-load it. For this to work, the file must indicate that it
% provides the feature via the \sfun{provide} function.
%\seealso{provide, _featurep, evalfile}
%!%-
public define require ()
{
variable f, file;
if (_NARGS == 2)
{
(f, file) = ();
}
else
{
f = ();
file = f;
}
if (_featurep (f))
return;
() = evalfile (file);
!if (_featurep (f))
vmessage ("***Warning: feature %s not found in %s", f, file);
}
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