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Scm2Xexpr - Scheme code formatter

Overview

The program listed below converts Scheme source code, stored in a specified file or text string, into PLT's Xexpr representation of XML. This can be used to generate web pages containing formatted Scheme code. The program listing below is generated by a PLT web servlet which uses this code.

About the code

The code was adapted from Dorai Sitaram's TeX2page, with the following changes:

• The Scheme formatting parts of TeX2page were extracted, and TeX-specific features removed.
• Generation of the HTML output string was changed to generate an Xexpr structure, and the output model was changed from imperative to purely functional.
• All possible mutable global variables were eliminated, to better support concurrent access in the web servlet context.
• Two remaining global variables, current-input and input-line-no, were changed to lexical variables. Access to these variables is shared by a number of the input-related functions. This allows concurrent requests to be served safely without resorting to the namespace tricks used by TeX2page as distributed with PLT, and without rearranging the code more drastically.

The resulting program is almost purely functional, with the only remaining imperative operation being the incrementing of the variable input-line-no, which is not currently used. The only other mutation involves the use of destructive reverse! for performance, and a once-per-request initialization of the lexical variable current-input.

Scm2Xexpr.scm

Syntax Highlighting: error: scm: undefined language

Pretty.scm

The following is a PLT web servlet which invokes the above code:

Syntax Highlighting: error: scm: undefined language