@hackage / xformat

This package is composed of two functions for formatted conversion between strings and typed values. Each is defined as a type-indexed function using a type class with multiple parameters and functional dependencies along with format descriptors.

Text.XFormat.Read allows one to parse values from a formatted string. Its functionality is similar to the C scanf function. Unlike scanf, however, the format descriptor is well-typed, ensuring that the output type is statically known.

Text.XFormat.Show allows one to print values to a formatted string. Its functionality is similar to the C printf function. Unlike printf, however, the format descriptor is well-typed, ensuring that the variable number arguments are statically known.

These functions can be easily extended to support new formats and new types. Extension is simple: define a format descriptor and an instance of the appropriate class.