Language Plugin

The goal of this project is to make prototypical implementation of a plugin for the Glasgow Haskell Compiler (GHC), such that the GHC can be used to compile programs that contain an implicit monadic effect.

Compatibility

This plugin only works with GHC 9.2 and cannot be used with other versions.

Examples

The plugin has been used to create two example languages.

• One Curry-Style functional logic language curry-ghc-language-plugin
• One strict language with IO side effects (similar to ML) ml-ghc-language-plugin

A fork of this has also been used to create a plugin for automatic function Inversion in Haskell. Details are in this paper and the project can be found at (https://github.com/cau-placc/inversion-plugin).

To capture all results of a nondeterministic computation, the user can import the computation in an ordinary Haskell module and use some of the following functions from Plugin.CurryPlugin.Encapsulation to get all results.

data SearchMode = DFS | BFS

--   Examples:
--   >>> $(evalGeneric DFS 'someNullaryFunction)
--   >>> $(evalGeneric BFS 'someUnaryFunction  ) arg1
--   >>> (..)
evalGeneric :: SearchMode -> Name -> Q Exp

--   Examples:
--   >>> $(evalN 0) DFS someNullaryFunction
--   >>> $(evalN 1) BFS someUnaryFunction   arg1
--   >>> (..)
evalN :: Int -> Q Exp

--   Examples:
--   >>> eval DFS someNullaryFunction
eval  :: _ => SearchMode
      -> Nondet a -> [b]

--   Examples:
--   >>> eval1 BFS someUnaryFunction arg1
eval1 :: _ => SearchMode
      -> Nondet (a1 --> b1) -> a2 -> [b2]

--   Examples:
--   >>> eval2 BFS someBinaryFunction arg1 arg2
eval2 :: _ => SearchMode
      -> Nondet (a1 --> b1 --> c1) -> a2 -> b2 -> [c2]

Examples and using the plugin in a sandbox

A sandbox project with examples is available to play around with in sandbox/. It can be loaded by executing stack repl sandbox from the root of the repository.

Known Issues

• Adding instances of derivable type classes to primitive types is not possible
• Sharing in let-expressions does not work in some edge-cases
• Using :r in GHCi only works on the second try
• Type errors sometimes mention the effectful versions of type constructors
• HIE and HaskellLanguageServer do not work
• Stack outputs some decoding failures while compiling the project. This can be ignored safely. Fixed with stack version 2.3.3

Debugging

In order see, when my plugin generates invalid code, use the GHC option -dcore-lint. This type checks the generated core-code and emits an error message when something went wrong. I am very interested in finding those issues. This option can also be turned on via {-# OPTIONS_GHC -dcore-lint #-}