Understanding the API

Main Classes and Packages

In Parsley, everything resides within the parsley package, and the major entry point is parsley.Parsley. There are a few modules of note:

• parsley.Parsley : contains some of the basic and primitive combinators (at least those that aren't methods on parsers).
• parsley.combinator : contains handy combinators, this should be your first port of call when you want to do something but are not sure a combinator exists for it. At the very least, the eof combinator is very common.
• parsley.character : contains a variety of combinators which deal with characters, key ones include char, satisfy and string.
• parsley.implicits : contains the very useful implicit conversion combinators. In particular, importing charLift and stringLift allows you write character and string literals as if they were parsers themselves. There are also implicit classes here which extend functions of any arity with a corresponding .lift method, instead of using the liftN functions.
• parsley.expr : contains the machinery needed to generate expression parsers for you based, at its simplest, on a table of operators in order of precedence. This is well worth a look (this is covered in detail in: Building Expression Parsers).
• parsley.token : contains a bunch of functionality for performing common lexing tasks, which is very configurable. These parsers may also be optimised for performance.

Using parsley.token for Lexing

Unlike Haskell libraries like megaparsec and parsec, parsley does not tie the lexing functionality to the Haskell Report, instead supporting a superset of the functionality. The functionality is provided to the user by parsley.token.Lexer, and this must be provided an value of type parsley.token.descriptions.LexicalDesc, which provides all the configuration necessary to describe the language and make the parsers.