load

(load filename &key verbose print if-does-not-exist external-format)

Reads a file and evaluates every top-level form in it in the global environment, then returns t. :if-does-not-exist is real: a false value answers nil instead of signalling when the file is not there, which is what makes (load "optional-config.lisp" :if-does-not-exist nil) work. The other three are accepted and ignored -- load produces no progress output, so :verbose and :print have nothing to do, and every backend reads UTF-8, so there is no second :external-format to select. Every option value is evaluated, in the order it was written, whether or not it is used. Definitions such as defun and setq in the loaded file remain available to subsequent code. A relative filename resolves against the directory of the file doing the load (the entry file for a top-level load), so a program can be run from any working directory and still find a (load "sibling.lisp"). In compiled output the loaded definitions live in the runtime eval interpreter's global environment, so they are reached through eval (e.g. (load "lib.lisp") then (eval '(square 5))). Works in all three backends; the WASM load reads the file with WASI path_open, so the module must be run with a directory granted (e.g. wasmtime run --dir . prog.wasm).

(load "lib.lisp")
(eval '(square 5))
(load "optional.lisp" :if-does-not-exist nil)

After loading a file that defines square, the definition is invoked through eval. The WASM backend needs --dir because it resolves the path against the preopened directories: a relative path against the first one, an absolute path against the preopened directory whose name is its longest prefix.

load is deliberately not idempotent: loading the same file twice evaluates it twice, matching Common Lisp. For load-once module semantics, see require / provide.