The functions in
require.sl facilitate the loading of S-Lang
Test whether or not a feature is present
Int_Type _featurep (String_Type feature [,String_Type namespace])
_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.
Declare that a specified feature is available
provide (String_Type feature [,String_Type namespace])
provide function may be used to declare that a "feature" has
been loaded into the specified namespace. If the namespace argument is not
present, the current namespace will be used.
See the documentation for
require for more information.
Make sure a feature is present, and load it if not
require (feature [,namespace [,file]])
String_Type feature, namespace, file;
require function ensures that a specified "feature" is present.
If the feature is not present, the
require function will attempt to
load the feature from a file. If the
namespace argument is present
and non-NULL, the specified namespace will be used. The default is to use
the current non-anonymous namespace. If called with three arguments, the
feature will be loaded from the file specified by the third argument
if it does not already exist in the namespace. Otherwise, the feature
will be loaded from a file given by the name of the feature, with
If after loading the file, if the feature is not present, a warning message will be issued.
require ("histogram"); require ("histogram", "foo"); require ("histogram", "foo", "/home/bob/hist.sl"); require ("histogram", ,"/home/bob/hist.sl");
"feature" is an abstract quantity that is undefined here.
A popular use of the
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
evalfile is that if the file has already been loaded,
will not re-load it.
provide, _featurep, evalfile