Interface files


This is a stub. Contributions, additions and corrections are greatly appreciated.

When an .agda file is saved, another file with the same name and extension .agdai is automatically created. The latter file is what we call an interface file.

Interface files store the results from the type-checking process. These results include:

  • A translation of pattern-matching definitions to case trees (this translation speeds up computation).

  • The resolution of all implicit arguments. (Note: under the option --allow-unsolved-metas not all implicit arguments need to be resolved to create an interface file.)


If an Agda file has one or more associated .agda-lib files, then the project root is the directory containing these files. In that case the Agda file’s interface file is stored in the directory _build/VERSION under the project root. Different directories are used for different versions of Agda so that one can switch between versions without losing the interface files.

If an Agda file does not have any associated .agda-lib file, then its .agdai file is stored in the same directory as the Agda file. (With at least one exception, see Agda bug #6134.)


When an .agda file is renamed, the old .agdai file is kept, and a new .agdai file is created. This is the intended behavior, and the orphan files can be safely deleted from the user’s file system if needed.

The compression run to create .agdai files introduces sharing. Sharing improves the memory efficiency of the code loaded from interface files.

The syntax represented in .agdai files differs significantly from the syntax of source files.


An external module is loaded by loading its interface file. Interface files are also intermediate points when compiling through a backend to e.g. Haskell.