This program is an reimplementation in Haskell 98 of

    Guy L. Steele, Jr. Building interpreters by composing monads. In
    Conference Record of POPL '94: 21st ACM SIGPLAN-SIGACT Symposium
    on Principles of Programming Languages, Portland, Oregon, January
    17-21, 1994, pages 472-492, New York, 1994. ACM Press.

    @inproceedings = { steele-building,
	author = "Steele, Jr., Guy L.",
        title = "Building Interpreters by Composing Monads",
        booktitle = "Conference record of {POPL} '94, 21st {ACM {SIGPLAN}-{SIGACT}} Symposium on Principles of Programming Languages: Portland, Oregon, January 17--21, 1994",
        publisher = "ACM Press",
        address = "New York, NY, USA",
        editor = "{ACM}",
        isbn = "0-89791-636-0",
        pages = "472--492",
        year = "1994",
        url = "citeseer.nj.nec.com/steele94building.html http://www.swiss.ai.mit.edu/~dae/related-papers/steele.ps.Z"
    }

My reimplementation uses constructor classes in Haskell 98 to avoid
the need for a program simplifier such as the one Steele described in
his paper.  I have tested my code using the Glasgow Haskell Compiler.
To compile, say

    ghc --make -fglasgow-exts -package util Main -lreadline # for GHC 5
    ghc --make -fglasgow-exts -package readline Main        # for GHC 6

I hope this reimplementation helps people study Steele's inspiring
work.  It has certainly helped me.  I would also appreciate any
feedback!

Finally, thanks to all participants in CS 252r: Advanced Functional
Programming, Spring 2001, Harvard University, for motivation and
insight.

Chung-chieh Shan <ccshan@cs.rutgers.edu>, 2001-04-30
http://www.cs.rutgers.edu/~ccshan/