Library Management

Agda has a simple package management system to support working with multiple libraries in different locations. The central concept is that of a library.

Example: Using the standard library

Before we go into details, here is some quick information for the impatient on how to tell Agda about the location of the standard library, using the library management system.

Let’s assume you have downloaded the standard library into a directory which we will refer to by AGDA_STDLIB (as an absolute path). A library file standard-library.agda-lib should exist in this directory, with the following content:

name: standard-library
include: src

To use the standard library by default in your Agda projects, you have to do two things:

  1. Create a file AGDA_DIR/libraries with the following content:

    AGDA_STDLIB/standard-library.agda-lib

    (Of course, replace AGDA_STDLIB by the actual path.)

    The AGDA_DIR defaults to ~/.config/agda on unix-like systems and C:\Users\USERNAME\AppData\Roaming\agda or similar on Windows. (More on AGDA_DIR below.)

    Remark: The libraries file informs Agda about the libraries you want it to know about.


  1. Create a file AGDA_DIR/defaults with the following content:

    standard-library

    Remark: The defaults file informs Agda which of the libraries pointed to by libraries should be used by default (i.e. in the default include path).

That’s the short version, if you want to know more, read on!

Library files

A library consists of

  • a name

  • a set of dependencies

  • a set of include paths

  • a set of default flags

Libraries are defined in .agda-lib files with the following syntax:

name: LIBRARY-NAME  -- Comment
depend: LIB1 LIB2
  LIB3
  LIB4
include: PATH1
  PATH2
  PATH3
flags: OPTION1 OPTION2
  OPTION3

Dependencies are library names, not paths to .agda-lib files, and include paths are relative to the location of the library-file.

Default flags can be any valid pragma options (see Command-line and pragma options).

Each of the four fields is optional. Naturally, unnamed libraries cannot be depended upon. But dropping the name is possible if the library file only serves to list include paths and/or dependencies of the current project.

The .agda-lib files associated to a given Agda file

When a given file is type-checked Agda uses the options from the flags fields of its library file (if there is such). If the command-line option --no-libraries is used, then no library file is used. Otherwise the library file is found in the following way:

  • First the file’s root directory is found. If the top-level module in the file is called A.B.C, then it has to be in the directory root/A/B or root\A\B. The root directory is the directory root.

  • If root contains any .agda-lib files, then the search stops. If there is exactly one such file, it is used, otherwise an error is raised.

  • If root contains no .agda-lib files, a search is made upwards in the directory hierarchy, and the search stops once one or more .agda-lib files are found in a directory. If no .agda-lib files are found all the way to the top of the directory hierarchy, then none are used.

Note also that there must not be any .agda-lib files below the root, on the path to the Agda file. For instance, if the top-level module in the Agda file is called A.B.C, and it is in the directory root/A/B, then there must not be any .agda-lib files in root/A or root/A/B.

Installing libraries

To be found by Agda a library file has to be listed (with its full path) in a libraries file

  • AGDA_DIR/libraries-VERSION, or if that doesn’t exist

  • AGDA_DIR/libraries

where VERSION is the Agda version (for instance 2.5.1). The AGDA_DIR defaults to ~/.config/agda on unix-like systems and C:\Users\USERNAME\AppData\Roaming\agda or similar on Windows, and can be overridden by setting the AGDA_DIR environment variable.

The AGDA_DIR will fall-back to ~/.agda, if it exists, for backward compatibility reasons. You can find the precise location of AGDA_DIR by running agda --print-agda-app-dir.

Each line of the libraries file shall be the absolute file system path to the root of a library, or a comment line starting with -- followed by a space character.

Environment variables in the paths (of the form $VAR or ${VAR}) are expanded. The location of the libraries file used can be overridden using the --library-file command line option.

You can find out the precise location of the libraries file by calling agda -l fjdsk Dummy.agda at the command line and looking at the error message (assuming you don’t have a library called fjdsk installed).

Note that if you want to install a library so that it is used by default, it must also be listed in the defaults file (details below).

Using a library

There are three ways a library gets used:

  • You supply the --library=LIB (or -l LIB) option to Agda. This is equivalent to adding a -iPATH for each of the include paths of LIB and its (transitive) dependencies. In this case the current directory is not implicitly added to the include paths.

  • No explicit --library option is given, and the current project root (of the Agda file that is being loaded) or one of its parent directories contains an .agda-lib file defining a library LIB. This library is used as if a --library=LIB option had been given, except that it is not necessary for the library to be listed in the AGDA_DIR/libraries file.

  • No explicit --library option, and no .agda-lib file in the project root. In this case the file AGDA_DIR/defaults is read and all libraries listed are added to the path. The defaults file should contain a list of library names, each on a separate line. In this case the current directory is also added to the path.

    To disable default libraries, you can give the option --no-default-libraries. To disable using libraries altogether, use the --no-libraries option.

Default libraries

If you want to usually use a variety of libraries, it is simplest to list them all in the AGDA_DIR/defaults file.

Each line of the defaults file shall be the name of a library resolvable using the paths listed in the libraries file. For example,

standard-library
library2
library3

where of course library2 and library3 are the libraries you commonly use. While it is safe to list all your libraries in library, be aware that listing libraries with name clashes in defaults can lead to difficulties, and should be done with care (i.e. avoid it unless you really must).

Version numbers

Library names can end with a version number (for instance, mylib-1.2.3). When resolving a library name (given in a --library option, or listed as a default library or library dependency) the following rules are followed:

  • If you don’t give a version number, any version will do.

  • If you give a version number an exact match is required.

  • When there are multiple matches an exact match is preferred, and otherwise the latest matching version is chosen.

For example, suppose you have the following libraries installed: mylib, mylib-1.0, otherlib-2.1, and otherlib-2.3. In this case, aside from the exact matches you can also say --library=otherlib to get otherlib-2.3.

Upgrading

If you are upgrading from a pre 2.5 version of Agda, be aware that you may have remnants of the previous library management system in your preferences. In particular, if you get warnings about agda2-include-dirs, you will need to find where this is defined. This may be buried deep in .el files, whose location is both operating system and emacs version dependant.