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This is a parser generator in the general style of yacc. See http://www.haskell.org/happy for downloads and documentation.


happy uses a language description file to create a Haskell module that will do the parsing. Typical usage in in the second stage of a compiler, where it will be used to generate an abstract syntax tree.

Input File Structure

A happy file consists of four parts.

  • The module header (Optional) : This is where you may define the module name and import other Haskell modules
  • Various directives : This is used for definition of the tokens, the type of scanner to use, precedence setting.
  • Grammar definition : The set of rules and actions
  • The module trailer (Optional) : More Haskell code that can be used in the actions.

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