atto is a compact, pure-functional, incremental text parsing library for Scala (if you're looking for binary parsing, please turn your attention to scodec). The atto API is non-invasive (nothing to extend!) and uses sensible and familiar abstractions. atto parsers are a fun and principled tool for everyday parsing.

scala> int.sepBy1(spaceChar).parseOnly("1 20 300").option
res0: Option[scalaz.NonEmptyList[Int]] = Some(NonEmptyList(1, 20, 300))

Current version is 0.4.2 and is available for Scala 2.10 and 2.11 with scalaz 7.1.

Notable changes since 0.4.1 include:

• atto is now published on Sonatype, so the Bintray resolvers are no longer needed.
• New character parsers whitespace, horizontalWhitespace, oneOf, and noneOf.
• New text parsers skipWhitespace and token for dealing with tokens.
• New text parsers bracket, parens, squareBrackets, braces, envelopes, and bananas for dealing with bracketed text.
• Additional syntax for .token, .parens, .sepBy*, .many*, and .skipMany*.
• Constructions that combine multiple parsers such as discard* and either are now strict only in the initial parser, which makes it easier to write recursive parsers that would otherwise need to use delay.

In addition to the above there were some logistical changes and a bug fix in optElem. For details on all changes please see the milestone.

Many thanks to the generous folks who contributed to this release:

• Rúnar Óli Bjarnason
• Adelbert Chang
• Jonathan Ferguson
• Alberto Jácome

Add atto as a dependency in your build.sbt file.

libraryDependencies += "org.tpolecat" %% "atto-core"  % "0.4.2"

if you are using Spire and want parsers for unsigned integral types you can also add atto-spire. Experimental integration with scalaz-stream is provided by atto-stream which can be added as above. This tiny library provides combinators to turn Parser[A] into Process1[String, A] with a few variations. There is a very basic example given here.

atto differs from stdlib parser combinators in a number of ways:

• You don't have to extend a trait or implement any methods.
• There is no tokenizer; the input type is always Char.
• Abstractions are better defined, which leads to simpler, more general code. Parser is a scalaz Monad for example, which gives us a lot of helpful operations for free.
• Parsers are incremental which means you can evaluate whether a prefix of your input is "ok so far." This can be helpful when working with streams or interactive UIs.

It's not a big deal to construct and use atto parsers; use them in any situation where you might otherwise reach for regular expressions or raw string manipulation.

Although atto is 50 times faster now than version 0.1, it's still not the fastest parsing lib on the block. If you're doing massive data processing you might look at a heavier library like Parboiled2, or even a hand-built parser like those used in the fastest JSON libs. But for "everyday" parsing where you have to turn user input into something useful, atto is a friendly little library to use.

Behold:

• A wee REPL tutorial.
• A variety of tasty examples.
• Read the source! Perhaps start with the parser definitions.

The core of atto originated in Edward Kmett's Scala port of Attoparsec. This library is an elaboration maintained by @tpolecat with contributions from some very helpful folks. Feedback and suggestions are always welcome.

Attoparsec, a Haskell library, is licensed under BSD-3 as specified here; the derivative work atto is provided under the MIT licence here. Both licenses appear in project metadata.