This module provides methods for common String transformations, similar to the Inflections library found in Rails:

http://api.rubyonrails.org/classes/ActiveSupport/Inflector.html

While many of the functions in this library are the same as in implementations in Rails' ActiveSupport, the philosophy of this library is fundamentally different. Where Rails tries to be as permissive as possible, and return a String when given any input, this library tries to output strings that make sense according to the function that is called.

When you look closely at many of the functions in Rails' inflections library, you will notice that many of them are partial. That is, they only have well-defined output for some of the possible inputs to the function allowed by the type system. As an example, let's take the underscore function. In Rails, it works like this:

>>> "fooBar".underscore
"foo_bar"

Looks ok so far. However, it's also easy to produce less expected results:

>>> "foo bar".underscore
"foo bar"

The output isn't underscored - it contains a space! It turns out that some of the functions from Inflections in ActiveSupport are partial. Ie., the outputs are really only specified for a certain range of the inputs allowed by the String type.

In the Haskell inflections library, we aim to deliver more predictable results by separating the parsing of strings into tokens from the application of transformations. Let's see an example.

First, we tokenize an underscored String using parseSnakeCase:

>>> parseSnakeCase [] "foo_bar"
Right [Word "foo",Word "bar"]

We can chain together the tokenization of the input String and the transformation to CamelCase by using LiftM:

>>> import Control.Monad (liftM)
>>> liftM camelize $ parseSnakeCase "foo_bar"

By separating out the tokenization from the application of inflections, we also end up with useful libraries for validating input which can be used independently:

>>> parseSnakeCase [] "fooBar"
Left "(unknown)" (line 1, column 4):
unexpected 'B'
expecting lowercase letter, "_" or end of input

This library is still a work-in-progress, and contributions are welcome for missing pieces and to fix bugs. Please see the Github page to contribute with code or bug reports:

https://github.com/stackbuilders/inflections-hs