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UIOP, the Utilities for Implementation- and OS- Portability

UIOP is the portability layer of ASDF. It provides utilities that abstract over discrepancies between implementations, between operating systems, and between what the standard provides and what programmers actually need, to write portable Common Lisp programs.

It is organized by topic in many files, each of which defines its own package according to its topic: e.g pathname.lisp will define package UIOP/PATHNAME and contain utilities related to the handling of pathname objects. All exported symbols are reexported in a convenience package UIOP, except for those from UIOP/COMMON-LISP. We recommend package UIOP be used to access all the symbols.

The files that constitute UIOP are, in dependency loading order:

  • package: deals with packages and their symbols, most notably including define-package, a variant of defpackage capable of hot-upgrade, or symbol-call and find-symbol* that are also useful for use in .asd files before packages have been defined.

  • common-lisp: lets you paper over various sub-standard implementations. Big offenders are Corman, GCL, Genera, MCL, all of them unmaintained. Supported without serious issues are: ABCL, Allegro, CCL, CMUCL, CLASP, CLISP, ECL, LispWorks, MKCL, SBCL, SCL, XCL.

  • utility: provides macros and functions that do not involve I/O; it handles control-flow, (p)lists, characters, strings, functions, classes, conditions, "stamps" (real number or boolean for +/- infinity), versions, etc. It also sports uiop-debug, a useful tool to help you debug programs.

  • os: extracts information from your environment, including an ABI identifier, features that distinguish Unix vs Windows, getenv, hostname, getcwd and chdir, etc.

  • pathname: overcomes the gruesome non-portability trap that are CL pathnames (and their lovecraftian "logical" variant), offering a vast array of functions and a sensible, usable abstraction to specify relative pathnames. It has a function merge-pathnames* to use instead of merge-pathnames, or even better, subpathname and its variant subpathname*; it has also plenty of functions for dealing with pathnames being directory vs file, physical vs logical, absolute vs relative, and more.

  • filesystem: provides portable access to the filesystem, inspecting it, only using truename when desired, using native OS namestrings, atomic file renaming, creating or deleting directories, etc.

  • stream: portably deals with *stderr* vs *error-output*, character encodings (external formats), element types, safe reading and writeing, opening files or temporary files, providing format-like designators for streams, flushing output buffers, consuming or copying streams, concatenating streams or files, copying files, etc.

  • image: portably deals with images, dumping them, restoring from them, registering hooks to run at suitable events in the image lifetime, printing backtraces, handling fatal conditions, using or avoiding debug modes, accessing command line arguments or quitting the process.

  • run-program: portably spawns external processes and captures their output. Can also capture error-output, inject input, or let it all be interactive.

  • lisp-build: portably compiles Common Lisp code, handles compilation results, muffles uninteresting conditions, saves and restores deferred warnings, runs hooks around compilation (to e.g. control optimizations or syntax), identifies the pathname of the current file, combines FASLs, etc.

  • configuration: portably locate and parse configuration files, using best practices to define and validate syntax, search standard paths, let users specify pathnames or pathname patterns, etc.

  • backward-driver: provides backward-compatibility with earlier incarnations of this library (i.e. ASDF internals that have leaked, ASDF-UTILS, or older versions of UIOP).

  • driver: reexports all the above utilities in a single package UIOP.

Documentation

Each file starts with a package definition form that lists the exported symbols.

All the exported functions, macros and variables ought to have proper docstrings. If not, then it's a legitimate bug that we invite you to report.

Maybe some automated tool will extract all that information and make a webpage from it, at which point it would be nice to insert a link here.

One tool with which you can extract all the documentation is HEΛP. At this time, the interface is not great: it isn't obvious at all that you can indeed use a scrollbar on the right of the top left side panel to navigate the many packages; once you click on the package you're interested in, you can see its defined symbols:

Another automated documentation tool is quickdocs, but unhappily, at the time of this writing, it only extracts information from the first package (see bug #24):

Help wanted extracting working documentation from UIOP's docstrings.

Using UIOP

UIOP is part of ASDF 3, and any modern Common Lisp implementation will have all of UIOP available when you (require "asdf"). NB: (require :asdf) also works on all implementations but CLISP.

If you need some functionality only available in a recent version of UIOP, but cannot or will not upgrade ASDF, UIOP is also distributed separately; see e.g. in Quicklisp. You may then have to load it like any other library:

(asdf:load-system :uiop)

If you want to use UIOP while preserving compatibility with ASDF 2, we recommend that in your ASDF system definition you may use the like of:

:depends-on (#-asdf3 :uiop)

Some history

UIOP, formerly known as ASDF-DRIVER (the package and system nicknames live on), evolved from ASDF 2's internal utilities and portability layer. It has since fully superseded functionality from the following libraries: ASDF-UTILS (UIOP carries on the ASDF 2 utilities that this exported), CL-FAD (UIOP's pathname and filesystem functions are much more portable), CL-LAUNCH (UIOP took its image and command-line argument handling), EXTERNAL-PROGRAM, TRIVIAL-SHELL and XCVB-DRIVER (UIOP's run-program evolved from XCVB-DRIVER's, and so did its condition muffling), SLIME's swank-loader (UIOP has better compilation and ABI identification), TRIVIAL-BACKTRACE (UIOP/IMAGE has all of it and more), etc.

UIOP also captures a large subset of the functionality from TRIVIAL-FEATURES, and a small subset of the functionality from ALEXANDRIA or FARE-UTILS.

We recommend you use UIOP instead of any of the above, where applicable, since UIOP is more portable, more robust, more ubiquitous, better designed, better documented, etc. If you see any way in which UIOP isn't superior, we're interested in improving it so it become so.