records-edsl: Write less record boilerplate

Cut off your boilerplate, eschew boilers entirely, and replace them with a small teapot perched atop a small but slightly foreboding volcano.

This package defines a small EDSL to define records.

Provides an eDSL for defining record data-types and a closed vessel in which fluid (generally water) is heated worth of boilerplate.

Defining a record type in this eDSL rather than plain Haskell gets you:

• Records without clashing names

• Syntax to access fields on records without Hungarian-notation prefixes on every field (via GHC.HasField and Optics.LabelOptic)

• Declarative syntax for defining that a field has an external representation you want to use for its, for example, ToJSON , FromJSON , or ToSchema

This is accomplished with the help of the excellent "witch" library.

• ToSchema instances with per-field field descriptions as per your comment on each field

• ToSchema instances with per-type descriptions

The EDSL also lets you extend what instances you get. The Deriver type defines how instances are defined.

Example:

We *can* write:

declareSchemaRecords deriveAll """
record Test --field-prefix=test {
  foo :: Int,
  bar :: MyType via MyTypeJSONRepr,
}
"""

But maybe you prefer:

data Test = Test
  { testFoo :: Int
  , testBar :: MyType
  }
  deriving stock (Show, Generic, Eq)
  deriving (Arbitrary) via (GenericArbitraryU Test)

instance O.ToSchema Test where
  declareNamedSchema _ = ...
  -- ... instance using 'foo' as 'Int' and 'bar' as 'MyTypeJSONRepr'
  -- converting 'bar' using @ 'from' @
  --
  -- I'm so allergic to writing this by hand that I can't even be
  -- bothered to put it into an example. Rest assured, it's annoying
  -- and easy to make mistakes with.

instance O.ToJSON Test where
  toJSON _ = ...
  toEncoding _ = ...
  -- ... instance using 'foo' as 'Int' and 'bar' as 'MyTypeJSONRepr'
  -- converting 'bar' using @ 'from' @.

instance O.FromJSON Test where
  parseJSON = ...
  -- ... instance parsing 'foo' as 'Int' and 'bar' as 'MyTypeJSONRepr'
  -- converting 'bar' using @ 'from' @

In actual examples the hand-written code is 8-10 times larger than with the declarative syntax.

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• records-edsl-0.1.0.tar.gz [browse] (Cabal source package)
• Package description (as included in the package)

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• MikeLedger

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