egg_recursive - Recursive interface for egg

This crate provides a recursive interface to egg. egg alrady comes with S-expression-based interface, but it has the following drawbacks:

• It uses FromStr and Display to parse/format textual representation of ASTs.
  • These CAN be used for other purposes and this can cause a conflict with other applications.
• Parser favours the first clause for terminal variants with the same parameter.
  • This can result in unexpected behaviour under the existence of ambiguity.
• ALL textual representation of ASTs fed to egg::rewrite is checked at RUNTIME.
  • This means we can't see syntax error until compilation;
  • This further complicates the debugging process.
• S-expressions get harder and harder to be parsed by human eyes

This crate alleviates these problems by introducing a recursive interface to egg.