Morley.Util.CustomGeneric

Generic deriving with unbalanced trees.

Custom Generic strategies

data GenericStrategy

Type of a strategy to derive Generic instances.

withDepths :: [CstrDepth] -> GenericStrategy

In this strategy the desired depths of contructors (in the type tree) and fields (in each constructor's tree) are provided manually and simply checked against the number of actual constructors and fields.

rightBalanced :: GenericStrategy

Strategy to make right-balanced instances (both in constructors and fields).

This will try its best to produce a flat tree:

• the balances of all leaves differ no more than by 1;
• leaves at left will have equal or lesser depth than leaves at right.

leftBalanced :: GenericStrategy

Strategy to make left-balanced instances (both in constructors and fields).

This is the same as symmetrically mapped rightBalanced.

rightComb :: GenericStrategy

Strategy to make fully right-leaning instances (both in constructors and fields).

leftComb :: GenericStrategy

Strategy to make fully left-leaning instances (both in constructors and fields).

haskellBalanced :: GenericStrategy

Strategy to make Haskell's Generics-like instances (both in constructors and fields).

This is similar to rightBalanced, except for the "flat" part:

• for each node, size of the left subtree is equal or less by one than size of the right subtree.

This strategy matches A1.1.

customGeneric "T" haskellBalanced is equivalent to mere deriving stock Generic T.

Entries reordering

reorderingConstrs :: EntriesReorder -> GenericStrategy -> GenericStrategy

Modify given strategy to reorder constructors.

The reordering will take place before depths are evaluated and structure of generic representation is formed.

Example: reorderingConstrs alphabetically rightBalanced.

reorderingFields :: UnnamedEntriesReorder -> EntriesReorder -> GenericStrategy -> GenericStrategy

Modify given strategy to reorder fields.

Same notes as for reorderingConstrs apply here.

Example: reorderingFields forbidUnnamedFields alphabetically rightBalanced.

reorderingData :: UnnamedEntriesReorder -> EntriesReorder -> GenericStrategy -> GenericStrategy

Modify given strategy to reorder constructors and fields.

Same notes as for reorderingConstrs apply here.

Example: reorderingData forbidUnnamedFields alphabetically rightBalanced.

alphabetically :: EntriesReorder

Sort entries by name alphabetically.

leaveUnnamedFields :: UnnamedEntriesReorder

Leave unnamed fields intact, without any reordering.

forbidUnnamedFields :: UnnamedEntriesReorder

Fail in case records are unnamed and we cannot figure out the necessary reordering.

Depth usage helpers

cstr :: forall n. KnownNat n => [Natural] -> CstrDepth

Helper for making a constructor depth.

Note that this is only intended to be more readable than directly using a tuple with withDepths and for the ability to be used in places where RebindableSyntax overrides the number literal resolution.

fld :: forall n. KnownNat n => Natural

Helper for making a field depth.

Note that this is only intended to be more readable than directly using a tuple with withDepths and for the ability to be used in places where RebindableSyntax overrides the number literal resolution.

Instance derivation

customGeneric :: String -> GenericStrategy -> Q [Dec]

Helpers

fromDepthsStrategy :: (Int -> [Natural]) -> GenericStrategy

Helper to make a strategy that created depths for constructor and fields in the same way, just from their number.

The provided function f must satisfy the following rules:

• length (f n) ≡ n

• sum $ (x -> 2 ^^ (-x)) <$> f n ≡ 1 (unless n = 0)

fromDepthsStrategy' :: (Int -> [Natural]) -> (Int -> [Natural]) -> GenericStrategy

Like fromDepthsStrategy, but allows specifying different strategies for constructors and fields.

Internals

reifyDataType :: Name -> Q (Name, Cxt, Maybe Kind, [TyVarBndr ()], [Con])

Reifies info from a type name (given as a String). The lookup happens from the current splice's scope (see lookupTypeName) and the only accepted result is a "plain" data type (no GADTs).

deriveFullType :: Name -> Maybe Kind -> [TyVarBndr flag] -> TypeQ

Derives, as well as possible, a type definition from its name, its kind (where known) and its variables.

customGeneric' :: Maybe Type -> Name -> Type -> [Con] -> GenericStrategy -> Q [Dec]

If a Type type is given, this function will generate a new Generic instance with it, and generate the appropriate "to" and "from" methods.

Otherwise, it'll generate a new Type instance as well.

makeRightBalDepths :: Int -> [Natural]

mangleGenericStrategyFields :: (Text -> Text) -> GenericStrategy -> GenericStrategy

Patch a given strategy by applying a transformation function to field names before passing them through ordering function.

mangleGenericStrategyConstructors :: (Text -> Text) -> GenericStrategy -> GenericStrategy

Patch a given strategy by applying a transformation function to constructor names before passing them through ordering function.