Getting Started with PLFA
Dependencies for users
You can read PLFA online without installing anything. However, if you wish to interact with the code or complete the exercises, you need several things:
PLFA is tested against specific versions of Agda and the standard library, which are shown in the badges above. Agda and the standard library change rapidly, and these changes often break PLFA, so using older or newer versions usually causes problems.
Installing Agda using Stack
The easiest way to install any specific version of Agda is using Stack. You can get the required version of Agda from GitHub, either by cloning the repository and switching to the correct branch, or by downloading the zip archive:
git clone https://github.com/agda/agda.git cd agda git checkout v220.127.116.11
To install Agda, run Stack from the Agda source directory:
stack install --stack-yaml stack-8.6.5.yaml
If you want Stack to use you system installation of GHC, you can pass the
--system-ghc flag and select the appropriate
stack-*.yaml file. For instance, if you have GHC 8.2.2 installed, run:
stack install --system-ghc --stack-yaml stack-8.2.2.yaml
Installing the Standard Library and PLFA
You can get the required version of the Agda standard library from GitHub, either by cloning the repository and switching to the correct branch, or by downloading the zip archive:
git clone https://github.com/agda/agda-stdlib.git cd agda-stdlib git checkout v1.1
You can get the latest version of Programming Language Foundations in Agda from GitHub, either by cloning the repository, or by downloading the zip archive:
git clone https://github.com/plfa/plfa.github.io
Finally, we need to let Agda know where to find the standard library. For this, you can follow the instructions here.
It is possible to set up PLFA as an Agda library as well. If you want to complete the exercises found in the
courses folder, or to import modules from the book, you need to do this. To do so, add the path to
~/.agda/libraries and add
~/.agda/defaults, both on lines of their own.
Setting up and using Emacs
The recommended editor for Agda is Emacs with
agda-mode. Agda ships with
agda-mode, so if you’ve installed Agda, all you have to do to configure
agda-mode is run:
To load and type-check the file, use
Agda is edited “interactively, which means that one can type check code which is not yet complete: if a question mark (?) is used as a placeholder for an expression, and the buffer is then checked, Agda will replace the question mark with a “hole” which can be filled in later. One can also do various other things in the context of a hole: listing the context, inferring the type of an expression, and even evaluating an open term which mentions variables bound in the surrounding context.”
Agda is edited interactively, using “holes”, which are bits of the program that are not yet filled in. If you use a question mark as an expression, and load the buffer using
C-c C-l, Agda replaces the question mark with a hole. There are several things you can to while the cursor is in a hole:
C-c C-c x split on variable x C-c C-space fill in hole C-c C-r refine with constructor C-c C-a automatically fill in hole C-c C-, goal type and context C-c C-. goal type, context, and inferred type
See the emacs-mode docs for more details.
If you want to see messages beside rather than below your Agda code, you can do the following:
- Open your Agda file, and load it using
C-x 1to get only your Agda file showing;
C-x 3to split the window horizontally;
- move your cursor to the right-hand half of your frame;
C-x band switch to the buffer called “Agda information”.
Now, error messages from Agda will appear next to your file, rather than squished beneath it.
agda-mode in Emacs
Since version 2.6.0, Agda has support for literate editing with Markdown, using the
.lagda.md extension. One side-effect of this extension is that most editors default to Markdown editing mode, whereas
In order to have
agda-mode automatically loaded whenever you open a file ending with
.lagda.md, put the following on your Emacs configuration file:
(setq auto-mode-alist (append '(("\\.agda\\'" . agda2-mode) ("\\.lagda.md\\'" . agda2-mode)) auto-mode-alist))
The configuration file for Emacs is normally located in
~/.emacs.d/init.el, but Aquamacs users might need to move their startup settings to the
Preferences.el file in
Using mononoki in Emacs
It is recommended that you install the font mononoki, and add the following to the end of your emacs configuration file at
;; default to mononoki (set-face-attribute 'default nil :family "mononoki" :height 120 :weight 'normal :width 'normal)
If you’re having trouble typing the Unicode characters into Emacs, the end of each chapter should provide a list of the unicode characters introduced in that chapter.
agda-mode and emacs have a number of useful commands. Two of them are especially useful when you solve exercises.
For a full list of supported characters, use
All the supported characters in
agda-mode are shown.
If you want to know how you input a specific Unicode character in agda file, move the cursor onto the character and type the following command:
You’ll see the key sequence of the character in mini buffer.
Dependencies for developers
PLFA is available as both a website and an EPUB e-book, both of which can be built on Linux and macOS. PLFA is written in literate Agda with Kramdown Markdown.
Building the website
The website version of the book is built in three stages:
.lagda.mdfiles are compiled to Markdown using Agda’s highlighter. (This requires several POSIX tools, such as
gem install bundler
Once you have installed all of the dependencies, you can build a copy of the book, and host it locally, by running:
make build make serve
The Makefile offers more than just these options:
make # see make test make build # builds lagda->markdown and the website make build-incremental # builds lagda->markdown and the website incrementally make test # checks all links are valid make test-offline # checks all links are valid offline make serve # starts the server make server-start # starts the server in detached mode make server-stop # stops the server, uses pkill make clean # removes all ~unnecessary~ generated files make clobber # removes all generated files
If you simply wish to have a local copy of the book, e.g. for offline reading, but don’t care about editing and rebuilding the book, you can grab a copy of the master branch, which is automatically built using Travis. You will still need Jekyll and preferably Bundler to host the book (see above). To host the book this way, download a copy of the master branch, unzip, and from within the directory run
bundle install bundle exec jekyll serve
Building the EPUB
The EPUB version of the book is built using Pandoc. Here’s how to build the EPUB:
Install a recent version of Pandoc, available here. We recommend their official installer (on the linked page), which is much faster than compiling Pandoc from source with Haskell Stack.
Build the EPUB by running:
The EPUB is written to