# YBlog - Parsec Presentation
Keywords: programming, haskell, parsec, parser

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# Parsec Presentation

tl;dr: Short introduction to Parsec for beginner.

- The html presentation is here.

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# Parsec

<author>by Yann Esposito</author>

<twitter> @yogsototh, </twitter> <googleplus> +yogsototh </googleplus>

for Riviera Scala Clojure Meetup (Haskell)
the 8 Oct 2013

## Parsing

Latin pars (ōrātiōnis), meaning part (of speech).

- analysing a string of symbols
- formal grammar.

## Parsing in Programming Languages

Complexity:

Method | Typical Example | Output Data Structure
--- | --- | ---
Splitting | CSV | Array, Map

Regexp

email

- Fixed Layout Tree

Parser

Programming language

- Most Data Structure

## Parser & culture

In Haskell Parser are really easy to use.

Generally:

- In most languages: split then regexp then parse
- In Haskell: split then parse

## Parsing Example

From String:

    (1+3)*(1+5+9)

To data structure:

## Parsec

> Parsec lets you construct parsers by combining high-order Combinators to create larger expressions.

> Combinator parsers are written and used within the same programming language as the rest of the program.

> The parsers are first-class citizens of the languages […]"

> Haskell Wiki

## Parser Libraries

In reality there are many choices:

attoparsec | fast
Bytestring-lexing | fast
Parsec 3 | powerful, nice error reporting

## Haskell Remarks (1)

spaces are meaningful

    f x   -- ⇔ f(x) in C-like languages
    f x y -- ⇔ f(x,y)

## Haskell Remarks (2)

Don’t mind strange operators (`<*>`, `<$>`).
Consider them like separators, typically commas.
They are just here to deal with types.

Informally:

    toto <$> x <*> y <*> z
    -- ⇔ toto x y z
    -- ⇔ toto(x,y,z) in C-like languages

## Minimal Parsec Examples

    whitespaces = many (oneOf "\t ")
    number = many1 digit
    symbol = oneOf "!#$%&|*+-/:<=>?@^_~"

    " \t " – whitespaces on " \t " "" – whitespaces on “32” “32” – number on “32”

    – number on "

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Published on 2013-10-09
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