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\layout Title

Implementing syntax-case and macromod
\newline 
(we want it now!)
\layout Author

Tony Garnock-Jones <tonyg@kcbbs.gen.nz>
\layout Abstract

Goals: understand syntax-case, implement in a non-bootstrapped manner (i.e.
 make no use of syntax-case in the implementation), ignore efficiency for
 clarity-of-implementation, second/alternative portable implementation,
 accumulate a library of useful syntactic-manipulation primitives, build
 Matthew Flatt's module system on top.
\layout Itemize

started with the simple system in the paper, with eager mark/subst propagation;
 then implemented lazy mark/subst propagation
\layout Itemize

strongly-typed separation between input syntax-objects (regular values +
 wrapped values) and output parsed-expressions - important
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use a trivial naive evaluator for RHS of macro definitions; lowest common
 denominator, can easily be improved upon
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subtlety in marking substitutions
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algorithmic refinements
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use of SRFI-1
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non-use of syntax-case
\layout Standard

Roughly 1000 lines of Scheme code for the syntax-case part - not a particularly
 complex program.
 Test-cases another 1000 lines.
 Once correctness achieved, adding better error-checking and features such
 as ellipsis-escaping and identifier-macros was very simple.
\layout Standard

Test-driven development a major benefit - without the test suite, development
 would have been several times slower.
 Having other implementations for cross-checking obviously also invaluable.
 psyntax in both sisc and chicken, mzscheme too; hosting this implementation
 in mzscheme and chicken provided for better testing that using a single
 underlying scheme implementation.
\layout Standard

Since syntax-case and syntax are both sugar for constructing syntax-objects,
 other useful constructs are a good idea: eg syntax->list from mzscheme,
 raw access to the b&p used by the expander itself, syntax-pair?, syntax-null?,
 ellipsis? etc etc.
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