Haskell, 10.12. Exercice.
N'oubliez pas la solution de nos problmes de planification (par ex. les cinq maris jaloux) l'aide des files prioritaires ! Haskell et parseurs monadiques (1) Ceci est un tutoriel de l'approche monadique au parsing. Il peut vous tre utile dans votre cours de compilation. L'approche fonctionnelle, monadique l'analyse syntaxique est une petite merveille algorithmique, permettant de travailler directement avec les lments des parseurs (analyseurs de syntaxe) de manire presque si simple, comme si ces modules taient des fragments de grammaire sous-jacente, et o le plug-in des procdures smantiques (constructeurs des rsultats du parsing) est facile et lisible. D'abord, il faut savoir quelque chose sur les grammaires formelles, et ici nous ne pouvons consacrer trop de temps... Imaginons - afin de nous rapprocher au mode de penser monadique - que la donne qui nous intresse, c'est ce rsultat, l'arbre en question. Donc, envisageons le protocole suivant. infixl 0 -*> P f -*> inp = f inp.
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. 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. This structure is passed between functions to allow them to see the current state of the parsing and create a new state. ConvertToNFA – This is the top level function, it is exposed externally and lets you convert a regex to a NFA. processOperator – This function determines when we should execute an operator given its precedence.
Last but not least are the methods which execute the operators. 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. In this article we will rewrite out compiler using a technique that has been used in parsers, especially those written in functional languages, for several decades now. 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? 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. We now need to be able to reduce the tree down to a single value (or error). Expression Reduction reduce :: (MonadError ExprError m) => ExpressionTree -> m Int We’re returning an Int, but as before, the context for this return value is an error state.The reducer is a really simple recursive function.
Reduce (Node (NNumber _ v) _) = return v Operator nodes recursively reduce their left and right child nodes, then apply the operator: 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).. You'll notice that I hardcoded in the header and footer of the latex output. I haven't done any performance testing but it feels pretty speedy (mac (intel) binary available here, it's nearly 600K because haskell bundles up its runtime so distributed exes are a bit large compared to their C equivalents... sigh) To run it from the command line: .
Anyway, here's the source code of the parser: 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. 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.