Contribution:
haskellParsec
Headline
Parsing in Haskell with Parsec
Motivation
The implementation demonstrates parsing in Haskell with the Parsec library of parser combinators. A concrete textual syntax for companies is assumed. Parse trees are constructed in accordance to an abstract syntax defined in terms of algebraic data types. We set up basic parsers for quoted strings and floating-point numbers. Further, we compose parsers for companies, departments, and employees using appropriate parser combinators for sequences, alternatives, and optionality. By design, the parser is kept simple in terms of leveraged programming technique; in particular, monadic style and applicative functors are avoided to the extent possible.
Illustration
See Contribution:haskellAcceptor for a basic illustrationof Parsec-based parsing. The present contribution is more complex in that it constructs proper parse trees.
parseDepartment :: Parser Department
parseDepartment = Department
<$> (parseString "department"
>> parseLiteral)
<* parseString "{"
<*> parseEmployee "manager"
<*> many parseSubUnit
<* parseString "}"
To this end, we use a parser type that is still parametric in the type of parse trees. Thus:
-- Shorthand for the parser type
type Parser = Parsec String ()
Relationships
- Contribution:haskellAcceptor is merely an acceptor as opposed to the proper parser at hand.
- Contribution:haskellVariation sponsored the data model used in the present contribution.
- Contribution:antlrAcceptor and others use the same textual representation.
Architecture
There are these modules:
- Main: parser test
- Company/Parser: the actual parser
- Company/Data: the abstract syntax definition
- Company/Sample: a baseline for testing at the level of abstract syntax
Usage
See https://github.com/101companies/101haskell/blob/master/README.md.
Backlinks
Ralf Lämmel
edited this article at
Sat, 20 Jun 2020 16:23:45 +0200
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