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# Replacing the Read Class
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## Problems with the Haskell 98 class
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- the backtracking parser is very inefficient
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- writing instances is painful, compared to a monadic interface
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- on failure, parsers give no indication of what went wrong
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## Proposed replacements
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- parsers based on [ ReadP](http://www.haskell.org/ghc/docs/latest/html/libraries/base/Text-ParserCombinators-ReadP.html), from [ Parallel Parsing Processes](http://www.md.chalmers.se/~koen/Papers/parsing-pearl.ps) by Koen Classen, JFP 2004.
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- monadic interface
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- supports nondeterminism without needing explicit committed choice
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- mostly deterministic parsers are much more efficient than `ReadS`
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- no error reporting
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- requires [PolymorphicComponents](polymorphic-components)
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GHC has used a new `Read` class based on these parsers since 5.04 (July 2002).
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- Malcolm's experimental Poly parser in the CVS version of HaXml?.
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- monadic interface
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- deterministic parser with committed choice
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- returns an error string on failure |
