Quicklisp and Package Management

ASDF (Another System Definition Facility) is the build tool that knows how to compile and load a collection of Lisp source files in dependency order, described by a .asd file; Quicklisp is the layer on top that knows how to find, download, and install a library and its transitive dependencies from a curated distribution called quicklisp-dists. When you run (ql:quickload :alexandria), Quicklisp resolves the dependency graph, fetches any missing archives from its mirror, and then hands off to ASDF to actually compile and load the .lisp files in the right order — the two tools solve genuinely different problems and neither replaces the other.

A library declares its own structure in a .asd file using asdf:defsystem, listing :depends-on for other systems it needs and :components for its own source files, often nested into modules with :file entries that specify load order explicitly. This declarative dependency graph is what lets ASDF avoid loading a file before its dependencies are ready — a utils.lisp defining a package must load before a main.lisp that uses symbols from that package, and defsystem's :serial t or explicit :depends-on component lists encode exactly that ordering constraint.

Quicklisp looks for systems in two places: its own downloaded dists under ~/quicklisp/dists, and a local-projects directory (~/quicklisp/local-projects/) that you can symlink your own in-development systems into, so (ql:quickload :my-app) picks up your working copy instead of a published release. For reproducibility across machines or CI, Quicklisp supports pinning to a specific dist version via ql-dist:install-dist with a dated release URL, or increasingly teams use Ultralisp (a rolling, more frequently updated distribution) or vendor dependencies directly rather than relying on quicklisp-dists' slower release cadence.