This flake defines how to build and run the Hugs Haskell interpreter on MacOS machines with the x86 chipset. Its quite likely that this source can build on M1, etc. but someone else will have to test that.

This flake builds from the last public source release of Hugs (September 2006). No updates were made to the source, except those necessary to get it to compile.

With nix installed and flakes enabled, you can build hugs quite easily. From the root of this repo:

$ nix build

The result symlink will point to a directory containing bin, hugsdir and some other directories:

• bin - Hugs interpreter and other executables (hugs, runhugs, ffihugs, cpphs-hugs and hsc2hs-hugs)
• hugsdir - This contains all the libraries that shipped with the last release of Hugs.

Hugs and friends can be run directly from this flake:

• nix run (that is, the default app) will execute runhugs, which expects a Haskell source file to execute.
• #hugs - Starts the Hugs interpreter.
• #runhugs - Executes runhugs (same as the default)
• #ffihugs - Executes the ffihugs program.
• #cpphs-hugs - Executes the cpphs-hugs program.
• #hsc2hs-hugs - Executes the hsc2hs-hugs program.

HUGSDIR is a compile time value that is used when resolving path names while searching for modules. By default, it will be set to the absolute path to the hugsdir directory in derivation's output (that is, the directory pointed to by result above).

man hugs explains how to override HUGSDIR and how to use it in conjunction with the search path (-P option) in order to find modules.

Ironically, the hardest part in getting hugs to build under Nix was due to whitespace handling. In the far past, someone mixed tabs and spaces throughout the hugs source code (Haskell files, specifically). gcc must have originally preserved whitespace, but clang (now the standard compiler provided by nix) did not. The file patches/sources.patch mostly updates indentation so hugs can compile its own source files.

I tried very hard to use cpphs (provided externally by nixpkgs) rather than patching all these source files, but there were just enough special defines and includes that clang already knew about that I couldn't quite get it working.

The C preprocessor provided by gcc also behaved slightly differently than clang. In particular, Haskell pragrams such as {-# INLINE #-} could not be split across multiple lines, such as:

{-# INLINE 
 #-}

As the preprocess would think the final line was a preprocess directive, and halt.

Some of the scripts in the source distribution seem plain bugged, as they were missing source files or preprocessor defines.

hsc2hs (built during bootstrapping) was hardcoded to use gcc; not surprising, clang didn't even exist when this was last released! gcc is provided by nix so the build can complete, and is also provided to the hsc2hs-hugs binary (though I'm not sure what that acutally does).