Complete integration with Edward Kmett's lens library while keeping the core polytropos packages free of the heavyweight transitive dependency tree.

Architectural Overview & Rationale

This module bridges polytropos flat runtime representations to standard lens abstractions: * Positional lenses: Field1 through Field9 instances on product records, so rec ^. _1 and rec ^. _2 read the first and second slots by position in \(O(1)\). * Name-based lenses: fieldLens focuses on a field by label symbol with literal index calculation via polytropos-plugin. * Container classes: Ixed and At instances keyed by field name for dynamic or symbol-indexed access. * Homogeneous traversals: Each instances over records whose fields share one type (AllFieldsAre). * Variant prisms: prismVariant constructs first-class Prism' optics for open variant constructors with \(O(1)\) tag matching.

When to Use This Module

• When your codebase heavily utilizes the full lens hierarchy (profunctor optics, indexed traversals, Field1..Field9).

When Not to Use This Module

• If you only need lightweight lenses and want to minimize dependencies, use Polytropos.Microlens instead.
• If your codebase uses the newer optics hierarchy, use Polytropos.Optics instead.

Worked Example

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeApplications #-}
{-# OPTIONS_GHC -fplugin=Polytropos.Plugin #-}

import Control.Lens
import Polytropos
import Polytropos.Lens

-- A genuinely heterogeneous record:
type Person = Record '["name" ':= String, "age" ':= Int]

person :: Person
person = REC { name = "Bob", age = 25 }

-- Positional heterogeneous access:
firstField :: String
firstField = person ^. _1  -- "Bob"

-- Name-based heterogeneous access:
ageVal :: Int
ageVal = person ^. fieldLens (Field @"age")  -- 25

-- Positional modification:
olderPerson :: Person
olderPerson = person & _2 .~ 26

-- Name-based modification:
olderPerson' :: Person
olderPerson' = person & fieldLens (Field @"age") %~ (+ 1)