Question

I’m going through Practical Common Lisp, I’m almost finished, and one question that has not been answered for me so far (or maybe I just missed it) is the difference between “require” and “load”.

So what is the difference?

Thanks.

Answer 1

require is used for modules, which can each consist of one or many files.

load is used to load an arbitrary single file.

The require function tests whether a
module is already present (using a
case-sensitive comparison); if the
module is not present, require
proceeds to load the appropriate file
or set of files. The pathname
argument, if present, is a single
pathname or a list of pathnames whose
files are to be loaded in order, left
to right. If the pathname argument is
nil or is not provided, the system
will attempt to determine, in some
system-dependent manner, which files
to load. This will typically involve
some central registry of module names
and the associated file lists.

Source: http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node119.html

The load function loads the file named by
filename into the Lisp environment. It
is assumed that a text (character
file) can be automatically
distinguished from an object (binary)
file by some appropriate
implementation-dependent means,
possibly by the file type. The
defaults for filename are taken from
the variable
default-pathname-defaults. If the filename (after the merging in of the
defaults) does not explicitly specify
a type, and both text and object types
of the file are available in the file
system, load should try to select the
more appropriate file by some
implementation-dependent means.

Source: http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node217.html