Epic - a Supercombinator Compiler

Introduction | Where to get it | Documentation

Epic is a simple functional language which compiles to reasonably efficient C code. The primary aim is to develop a back end for Epigram, but it will (I hope, eventually) be useful to anyone looking for a back end for a functional language. It is currently used as a back end for Idris.

Programs consist of a number of supercombinator definitions, e.g. the canonical factorial example or this list program. The main function is evaluated when the program is run. Some important language features to note:

• Strict semantics by default, with lazy annotation if that's what you need.
• No semantic checking, other than to see if names are in scope --- it is assumed that the higher level language will have performed typechecking, and in any case Epic should make no assumptions about the higher level type system or any transformations you've applied. Type annotations are required, but they only give hints to the compiler (I might change this).
• Further to the above, if you get a segmentation fault, it might be an error in my code, but it might also be a type error. I may add a debug mode with dynamic checking to help here.
• Data types are introduced with an explicit constructor tag; e.g. Con 2 (x,y,z) is a constructor taking three arguments, with tag 2.
• There is a rudimentary foreign function interface, allowing calls to external C functions. Foreign functions can have side effects, and it is assumed that you've set things up so that they evaluate in the right order... see this program for a simple example.
• ';' is a sequencing operator, for sequencing side effecting expressions.
• Primitive types Int, Float, BigInt, BigFloat, Char and String, although only Int, BigInt and String work so far; comparison operators work on Int.

If you try it and find features you need are missing or that things do not work as you expect, please let me know.

Epic is available either through the repository on github, or from hackage with the usual warnings about research quality code, etc:

• git clone git://github.com/edwinb/EpiVM.git
• Epic on Hackage.

To build it, either use Cabal, or:

• make configure
• make install, to install just the API, or make epic_install to install the command line compiler, epic.

You'll need an up to date GHC, happy, the Boehm garbage collector library and the GNU MP arithmetic library. You'll also need gcc, since the compiler outputs C code. Please let me know how you get on! I've tested this on Linux (Debian and Ubuntu) and Mac OS X 10.4. Packages for all the required libraries are available for both.

There is an API (haddock generated documentation) and a command line tool. The API is currently minimal, but will eventually be extended to allow building of syntax trees from Haskell programs, rather than requiring an ASCII source file.

The command line tool, epic takes a source file and produces executable code, via C. Separate compilation is supported, in a fairly simple way, e.g. to compile a main program main.e which includes some functions defined in lib.e:

• Build lib.o with the command epic -c lib.e.
• Import functions in main.e with the line include "lib.ei" in the source.
• Build the executable with epic main.e lib.o -o main

Edwin Brady -- eb@cs.st-andrews.ac.uk --