typed-encoding

Type level annotations, string transformations, and other goodies that make programming strings safer.

Motivation

I have recently spent a lot of time troubleshooting various Base64, quoted-printable, and UTF-8 encoding issues.
I decided to write a library that will help avoiding issues like these.

This library allows to specify and work with types like

-- some data encoded in base 64
mydata :: Enc '["enc-B64"] ByteString

-- some text (utf8) data encoded in base 64 
myData :: Enc '["enc-B64", "r-UTF8"] ByteString

It allows to define precise string content annotations like:

ipaddr :: Enc '["r-IpV4"] Text

and provides ways for

• encoding
• decoding
• recreation (encoding validation)
• type conversions
• converting types to encoded strings
• typesafe conversion of encoded strings to types

... but this approach seems to be a bit more...

-- upper cased text encoded as base64
example :: Enc '["enc-B64", "do-UPPER"] () T.Text
example = encodeAll . toEncoding () $ "some text goes here"

It becomes a type directed, declarative approach to string transformations.

Transformations can be

• used with parameters
• applied or undone partially (if encoding is reversible)

One of more interesting uses of this library are encoding restrictions.
(Arbitrary) bounded alpha-numeric (r-ban) restrictions and a simple annotation Boolean algebra are both provided.

phone :: Enc '["r-ban:999-999-9999"] () T.Text
phone = ...

-- simple boolean algebra:
phone' :: Enc '["boolOr:(r-ban:999-999-9999)(r-ban:(999) 999-9999)"] () T.Text
phone' = ...

Examples

Please see Examples.TypedEncoding it the module list.

Other encoding packages

My approach will be to write specific encodings (e.g. HTTP) or wrap encodings from other packages using separate "bridge" projects.

Currently typed-encoding depends on

• base64-bytestring because it was my driving example, this is likely to move out to a separate bridge project at some point.

Bridge work:

• typed-encoding-encoding bridges encoding package

Plans, some TODOs

• lensifying conversions
• better implementation type safety

Tested with

• stack (1.9.3) lts-14.27 (ghc-8.6.5)
• needs ghc >= 8.2.2, base >=4.10 for GHC.TypeLits support

Known issues

• running test suite: cabal has problems with doctest, use stack
  https://github.com/haskell/cabal/issues/6087