named-records: Flexible records with named fields.

Flexible records with named fields.

v0.2

Default values with record.

v0.2.1

Requires names-0.2.1.

v0.2.2

TH record definitions allow for more types to be used in the definition.

Named records allow you to define und use records with labeled fields. These records are first class objects. Record fields are labeled by names, which can basically be any type. However, the names package provides global name types and some syntactic sugar to use them.

Here is a complete walk-through, with Template Haskell syntactic sugar.

This is how a typical example preamble looks like:

{-# LANGUAGE Haskell2010, TemplateHaskell #-}

import qualified Data.Name
import Data.NamedRecord

In order to use names you need to declare them first (see the names package for further details):

name "firstName"
name "lastName"

These are two records Person and User:

record "Person"
    `has` "firstName" := ''String
    `has` "lastName"  := ''String

record "User"
    `has` "firstName" := ''String
    `has` "lastName"  := ''String
    `has` "loginName" := ''String

Note that these declarations create constructor functions newPerson and newUser, as well as type synonyms Person and User (use -ddump-slices to see what has been generated).

Here are two instances of these recors:

julian = newPerson
   `set` firstName := "Julian"
   `set` lastName  := "Fleischer"

alexander = newUser
   `set` firstName := "Alexander"
   `set` lastName  := "Carnicero"
   `set` loginName := "alexander.carnicero"

We can now create a displayName function like the following:

displayName obj =
    (obj `get` firstName) ++ " " ++
    (obj `get` lastName)

Note that this function will accept any record that has a firstName and a lastName field of type String.

>>> displayName julian
Julian Fleischer

>>> displayName alexander
Alexander Carnicero

As mentioned above, records are first class citizens. That means you can create them anywhere:

>>> displayName (firstName := "John" :+ lastName := "Doe")
John Doe

Modules

[Index]

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• named-records-0.2.2.tar.gz [browse] (Cabal source package)
• Package description (as included in the package)

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• JulianFleischer

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