Haskell, 10.12. Packrat Parsing: a Practical Linear-Time Algorithm with Backtracking. Abstract Packrat parsing is a novel and practical method for implementing linear-time parsers for grammars defined in Top-Down Parsing Language (TDPL).
While TDPL was originally created as a formal model for top-down parsers with backtracking capability, this thesis extends TDPL into a powerful general-purpose notation for describing language syntax, providing a compelling alternative to traditional context-free grammars (CFGs). Common syntactic idioms that cannot be represented concisely in a CFG are easily expressed in TDPL, such as longest-match disambiguation and "syntactic predicates," making it possible to describe the complete lexical and grammatical syntax of a practical programming language in a single TDPL grammar. Packrat parsing is an adaptation of a 30-year-old tabular parsing algorithm that was never put into practice until now. Haskell - Writing a Regular Expression parser in Haskell: Part 2 - Matthew Manela - Farblondzshet in Code.
The first module in my simple regular expression parse is called RegexToNFA.
This module exposes the types that make up a finite state machine and also the functions to convert a regular expression string into a finite state machine. My structure for a FSM follows closely from the mathematical definition: I have the value which you transition on as a Maybe Char (which I alias as TransitionValue). This allowed me to define epsilon as Nothing data constructor. With this structure defined my goal now is to convert a regular expression pattern such as: (a|b)* into a FiniteMachine. Interp.pdf (Objet application/pdf) Let's build a compiler (in Haskell): Part 7 - Parser Combinators at AlephNullPlex. Tags: < Part 6 Our parser has served us well so far.
We can successfully parseAndEmit simple mathmatical expressions as well as assignments. However the technique used so far, one big parse function, has some serious drawbacks. Not least is the fact that it is starting to get too long and complicated. A simple regex engine in Haskell. UPDATE: sorear from #haskell pasted a cool version of this here.
His version is a Parsec Parser that returns another Parsec Parser! How cool is that? His version doesn't actually return the matches themselves, just a Bool, but still, it's a clever hack. Rediscover the Joy of Coding. In the last three articles I covered the overall structure, lexer, and parser of a simple expression evaluator.
This articles concludes by presenting the evaluator and main loop. At this stage we are able to take a string, tokenize it, and then build a tree representing the expression. 117337.pdf (Objet application/pdf) Haskell Textile to HTML/Latex parser. Yayfun.
I like writing in textile (RedCloth), it's less intrusive than doing "pure" latex when I'm authoring documents but I still get that nice warm fuzzy of being able to author docs in plain text. Yeah, I'm a geek. Anyway since I couldn't find any textile to latex parsers I whipped one up in Haskell for a reasonable subset of textile (it's not very big). I'm sure it's not 100% compatible with the other implementations out there but it's for my purposes and I'm going to be open sourcing it when the opens.snepo.com is finally (whenever that may be).. Neil Mitchell - TagSoup. TagSoup is a library for parsing HTML/XML.
It supports the HTML 5 specification, and can be used to parse either well-formed XML, or unstructured and malformed HTML from the web. The library also provides useful functions to extract information from an HTML document, making it ideal for screen-scraping. The library provides a basic data type for a list of unstructured tags, a parser to convert HTML into this tag type, and useful functions and combinators for finding and extracting information. Related Projects. Parsec, a fast combinator parser. Daan Leijen University of Utrecht Dept. of Computer Science PO.Box 80.089, 3508 TB Utrecht The Netherlandsdaan@cs.uu.nl, 4 Oct 2001 Introduction Parsec is an industrial strength, monadic parser combinator library for Haskell.
Parser un format simple en Haskell avec Parsec.