Enables polytropos open records to act as beam database schema tables without GHC out-of-memory compilation crashes on 50+ columns.

Architectural Overview & Rationale

Eliminating Generic Tree Explosion in Beam

A standard beam table is a nominal Haskell record whose Beamable instance is derived through GHC.Generics. The resulting binary metadata tree is what causes quadratic compile times and memory blow-up on tables with 50+ columns.

In polytropos-beam, a table is backed by a single flat SmallArray: * zipBeamFieldsM executes as a linear lockstep walk over flat array slots. * tblSkeleton builds the table spine once per row arity. * BeamTable is a zero-cost newtype wrapper around RowRep f ProductRowT r ().

When to Use This Module

• When defining large database tables (dozens or hundreds of columns) with the beam framework while maintaining predictable, instantaneous compilation.

Worked Example

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE OverloadedRecordDot #-}

import Database.Beam
import Polytropos
import Polytropos.Beam

type UserRow = '["id" ':= Int, "username" ':= String]
type UserTable f = BeamTable UserRow f

-- 1. Construct an open record using idiomatic REC syntax:
userRec :: Record UserRow
userRec = REC { id = 1, username = "Alice" }

-- 2. Convert to a Beam database table (zero-cost unwrap):
userTable :: UserTable Identity
userTable = toBeamTable userRec

-- 3. Functional updates using REC_UPD prior to database serialization:
updatedUser :: Record UserRow
updatedUser = (REC_UPD userRec) { username = "Bob" }

-- 4. Higher-Kinded Data (HKD) partial table with REC_F and REC_UPD_F:
partialUser :: RecordF Maybe UserRow
partialUser = REC_F { id = Just 1, username = Nothing }

populatedUser :: RecordF Maybe UserRow
populatedUser = (REC_UPD_F partialUser) { username = Just "Bob" }