woe alternatives and similar packages
Based on the "Data" category.
Alternatively, view woe alternatives based on common mentions on social networks and blogs.
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streaming
An optimized general monad transformer for streaming applications, with a simple prelude of functions -
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text-icu
This package provides the Haskell Data.Text.ICU library, for performing complex manipulation of Unicode text. -
WorkOS - The modern identity platform for B2B SaaS
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README
woe
Convenient typeclass for defining arbitrary-index enums, which allow for safe derivation of Enum using DerivingVia.
The Problem
In certain cases (e.g. server emulation), we may find ourselves stuck with reimplementing shoddy serverside logic due to how the original game chose to encode its enumerations for de/serialization in the networking and datafiles. These enums tend to be huge (up to 200+ entries), contain unks, and at times have "holes" in the valid indices of the enumeration.
Haskell's Enum typeclass has two major issues that stand in the way of this:
- Safety
Although Enum is already "dangerous" as-is due to the use of error upon an invalid index lookup, it is even more
dangerous in the case of discontinuous enumeration ranges.
- Redundant Declarations
To implement Enum, one has to write "duplicate" code for both toEnum and fromEnum. This leads to what I call the
2*n declaration problem. If you have 200 items in your enum ADT, you have to write 400 declarations. The best part is,
writing updating such large and redundant Enum implementations is highly error-prone and may lead to an unintentional
violation of Enum's isomorphicity law (fromEnum . toEnum = id).
The Solution
woe introduces the typeclass IsoEnum and the wrapper newtype WOE (Write-Once Enum) to solve the above problems. The acronym sounds a bit lame
and unoriginal, but I digress.
For safety, woe provides toEnumSafely and fromEnumSafely for instances of IsoEnum. These return a Maybe result
in the event of a unimplemented enum value or bad index. Additionally, WOE allows one to
derive Enum on their type using deriving (Enum) via WOE MyType, thereby avoiding the "sin" of a blanket Enum
instance over all IsoEnum instances.
To solve redundant declarations, IsoEnum provides a single method, mapping :: [(Int, a)], that allows you to declare
each index-value exactly once. Should you update it, you will only have to update a single pair instead of two. Should
you want an (arguably unsafe) Enum instance for your type instead of relying on just to/fromEnumSafely, again, use deriving (Enum) via WOE MyType.
Example
import Data.WOE
data FriendRegistrationResult
= FriendRegistered
| NoEmptyFriendSlots
| RequestRefused
| RecipientAlreadyAFriend
| RecipientNotOnline
| RecipientHasNoEmptyFriendSlots
| RecipientBlockedFriendRequests
| GenericError
deriving (Eq)
deriving (Enum, Describable)
via WOE FriendRegistrationResult
Note: Describable is a separate typeclass from my describe package. But this demonstrates an additional benefit
of deriving via WOE: avoiding blanket de/serialization typeclass instances over all implementations of Enum or IsoEnum, which can (and will) lead to ambiguities.