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Grammar Spec (gspec) Processing Tool

This directory contains a simple tool for processing programming-language grammar specifications. The idea is to allow a single specification to be used to generate multiple textual representations (e.g., LaTex and Asciidoc).

Notation

  • symbol names: symbol names are identifiers that start with a letter and can contain letters, decimal digits, dashes ('-'), underscores ('_'), and single quotes (''').

  • literal terminal symbols: a literal terminal is specified by enclosing it in single quote characters; e.g., 'if'.

  • terminal symbols: a terminal symbol name enclosed in double quotes; e.g., "identifier".

  • non-terminal symbols: a non-terminal symbol name enclosed in angle brackets; e.g., <expression>.

  • labels are identifiers enclosed in [ ]

  • comments start with the # character and run to the end of the current line. There is a special form of a comment, called a note, that starts with the characters #< and which is attached to the proceeding production.

Syntax

The following grammar (specified using the above notation) describes the syntax of grammar specs:

[gspec] {
  <spec>    : <content>

  <content> : <section>+
            | <rule>+

  <section> : "label" '{' <content> '}'

  <rule>    : "label"? "non-term" ':' <rhs> ( '|' <rhs> )*

  <rhs>     : "label"? 'empty' "note"?
            | "label"? <phrase>+ "note"?

  <phrase>  : <symbol>
            | <symbol> <repeat>
            | '(' <phrase>+ ')' <repeat>

  <symbol>  : "non-terminal"
            | "terminal"
            | "literal"

  <repeat>  : " '?' | '*' | '+'
}

Grammar Sections

A grammar can be specified as a sequence of CFG rules or as a heirarchy of labeled sections, where the innermost sections contain CFG rules.

Sections provide a mechanism for splitting a specification across multiple output files. For example, if we have a grammar specification in the file lang.gspec that has the following structure

[foo] {
  [bar] { ... }
  [baz] { ... }
}

then there will be two output files generated: lang-foo-bar.out and lang-foo-baz.out (where out is the file suffix for the target format).

Targets

We currently envision three targets for the gspec tool (of which two are currently implemented). These are

  • LaTeX using the grammar.sty file that is provided in the support directory

  • LaTeX using the syntax.sty package that comes with most TeX distributions. (not yet implemented)

  • HTML via asciidoctor. This target produces Asciidoc files that can be used to generate HTML. The grammar.css support file defines styles for the different kinds of grammar symbols.