Alfa has a simple plug-in interface, allowing
Haskell programmers to
write plug-in modules that extends Alfa's core functionality in various
The intention is that it should be possible develop and distribute plug-ins
separately from Alfa, but for the time being, plug-in modules
have to be hardwired into Alfa. (This is because current Haskell
implementations do not support dynamic code loading.)
Alfa currently comes with a small number of plug-ins:
Most of these are in an experimental and/or undocumented state...
- translates formal proofs (i.e., definitions and expressions in
Alfa) to natural language. At present, there is support for
English, French and Swedish, but more languages can be added by
the user. (It is called GF because it is implemented using the
Grammatical Framework, GF.)
- use Alfa as an alternate user interface to the GF.
- generate equality relations for data types.
- generate natural deduction style proofs for
propositional logic formulas.
- a simple test of the plug-in interface.
Allows plain text files to be opened in Alfa. Counts how many
times a file has been saved and reopened.
Activating plug-in modules
When starting Alfa, no plug-ins are activated by default. By supplying
all plug-ins are activated. You can selectively activate some
plug-ins by supplying a colon-separated list after the
alfa - -plugins
-plugins flag, e.g.,
alfa - -plugins GF:Pesca
alfa - -plugins Derive
Alfa announces the activation of a plug-in in the terminal window when
Alfa is started. Plug-ins usually also announce their presence in the
info display, at the bottom of Alfa's window, when the entire document
Exactly how to use a plug-in depends on the plug-in, of course. In
general, users interact with plug-ins through extra commands that appear
in the menus. The commands can provide
Additionally, plug-ins can
- new ways to construct/modify definitions and expressions.
- alternate views (e.g. natural language text in GF) of definitions and
- Display additional information about selected parts of the document.
- Allow files in other formats to be opened and converted to Alfa
- Put plug-in-specific extra information in saved documents.