Replacing the Read Class

Problems with the Haskell 98 class

• the backtracking parser is very inefficient

• writing instances is painful, compared to a monadic interface

• on failure, parsers give no indication of what went wrong

Proposed replacements

• parsers based on  ReadP, from  Parallel Parsing Processes by Koen Classen, JFP 2004.
  • monadic interface
  • supports nondeterminism without needing explicit committed choice
  • mostly deterministic parsers are much more efficient than ReadS
  • no error reporting
  • requires PolymorphicComponents
• GHC has used a new Read class based on these parsers since 5.04 (July 2002).

• Malcolm's experimental  Poly parser in the CVS version of  HaXml.
  • monadic interface
  • supports non-determinism but also has deterministically committed path (like cut operator in prolog)
  • returns an error string on failure

• Could also use something based on Daan's Parsec combinators
  • monadic interface
  • mostly deterministic, with explicit 'try' operator for non-determinism
  • error-reporting
  • already widely used for other parsing tasks

Tickets

#61

replace the Read class