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Parser combinator operators in Swift

FootlessParser  

This is part of a series on FootlessParser, a parser combinator written in Swift.


Parser combinators must be one of the best things to come out of functional programming. They let you define intuitive parsers right in the code, without any need for pre-processors.

Like this:

let parser = function1 <^> parser1 <*> parser2 <|> parser3

where function1 and parser3 return the same type.

parser will pass the input to parser1 followed by parser2, pass their results to function1 and return its result. If that fails it will pass the original input to parser3 and return its result.

FootlessParser: updated documentation and readme

FootlessParser  

The FootlessParser project is finally becoming usable and now has brand-new documentation generated by jazzy. The readme has also received some attention and is now actually useful:


FootlessParser is a simple and pretty naive implementation of a parser combinator in Swift. It enables infinite lookahead, non-ambiguous parsing with error reporting.

Also check out a series of blog posts about the development and documentation from the source code.

Add Result type and operators

FootlessParser  

This is part of a series on FootlessParser, a parser combinator written in Swift.


Add Runes and LlamaKit using Carthage

https://github.com/kareman/FootlessParser/commit/6142452334dae45a5aae65e0f54264f1ea3f533d

Footlessparser is using operators for map ( <^> ), flatmap/bind ( »- ) and apply ( <*> ). Luckily the Runes framework has already defined these, and implemented them for optionals and arrays.

Each parse returns a Result, which has either a tuple containing the output and the remaining unparsed part of the input, or an error description if parsing fails. The Result enum is in the Llamakit framework, later replaced by antitypical/Result.

Set up an open source Xcode framework project

FootlessParser  

This is part of a series on FootlessParser, a parser combinator written in Swift.


I find these steps helpful when setting up any new open source framework project in Xcode.

Create project

https://github.com/kareman/FootlessParser/commit/414e3961d3bb2a2df8a257804534578bc7a06461

Create a new project in Xcode, and select OS X framework if it is for both iOS and OS X. The iOS framework target can be added later, besides OS X frameworks are more practical for unit testing. No simulators needed.

Do not select to add it to Git right away. Because of this.

And that’s it. I so do love a fresh project.

Introduction to FootlessParser

FootlessParser  

This post is part of a series on FootlessParser, a parser combinator written in Swift.


The goal is to define parsers like this:

let parser = function1 <^> parser1 <*> parser2 <|> parser3

where parser will pass the input to parser1 followed by parser2, pass their results to function1 and return its result. If that fails it will pass the original input to parser3 and return its result.

Writing a parser combinator in Swift

FootlessParser  

This post is part of a series on FootlessParser, a parser combinator written in Swift.


Before Swift my only contact with functional programming was a couple of half-hearted attempts at reading Erlang, all of them resulting in me running away screaming, clutching my aching head. But learning functional concepts in Swift proved far easier, probably because the syntax is closer to what I was used to. So I read Functional Programming in Swift and everything was well and good until one of the last chapters, “Parser Combinators”, and the headache was back. Luckily I managed to stay quiet and in place this time. I downloaded the code for the chapter, turned it into a framework and hacked away until I had implemented a CSV parser, but I still didn’t really understand it.