Eucalypt implementation

At 0.1.x very little effort has been spent on performance or other quality of implementation aspects in comparison to attributes which aid experimentation or evolution of the tool. In fact, the main reason it is currently written in Haskell is just for the ease of defining and redefining the various syntax data structures. It should be "fast enough" for the intended use cases but would completely suck in any compute intensive benchmarks.

When you run eu, the execution consists of several phases:

  • parsing inputs to abstract syntax trees
  • transformation into a core syntax and merging and manipulation of these representations
  • compilation into STG syntax
  • execution which is interpretation of the STG syntax by the STG machine

The core syntax facilitates experimentation by allow powerful features to be implemented simply by syntax transformation (e.g. user definable operator precedence, block catenation).

It is also in transformation to core syntax that the two roles of blocks in Eucalypt (name binding and data structuring) are peeled apart into separate elements (a recursive let and a data structure).

The interpreter is modeled on an eval-apply STG (spineless tagless G-machine) implementation simply to have a well defined reference point in view for a lazy functional language abstract machine, not for any other reason (concurrency etc.) Ultimately it could well be quicker and clearer to tree-walk the core representation.

The machine is parasitic on the garbage collection of the underlying implementation runtime (Haskell) by attempting to be economical with the heap references to it maintains.

While these phases are reminiscent of Haskell's own (GHC) implementation, the resemblance is shallow and crude. Eucalypt's core syntax is untyped, the STG syntax differs and the machine is an interpreter, not a compiler.

Diagnostics

Raw ASTs can be dumped (as JSON) using the -p command line switch.

Core syntax can be dumped at various stages using a variety of --dump-xxx command line switches.

The final STG syntax which is executed by the STG machine may be dumped using --dump-stg