polytropos-plugin

GHC typechecker plugin synthesizing literal dictionaries and \(O(1)\) jump tables directly into Core AST for polytropos.

Overview

In traditional Haskell row libraries, solving field offsets or dictionary instances involves either:

1. Recursive type-level search (\(O(N)\) or \(O(N^2)\) compile-time scaling).
2. Runtime dictionary passing and pointer chasing.

polytropos-plugin solves evidence constraints (FieldIndex, ConstructorIndex, RowEq, RowShow, RowEqSum, RowShowSum, AllFields) by inspecting the row at compile time and emitting literal slot indices, tags, and dictionary vectors directly into GHC Core AST.

Usage

Enable the plugin in your .cabal file or module:

build-depends:
    polytropos-core >= 0.1 && < 0.2
  , polytropos-plugin >= 0.1 && < 0.2

ghc-options: -fplugin=Polytropos.Plugin

Quick Example

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

import Polytropos

type User = Record '[ "name" := String, "score" := Int ]

main :: IO ()
main = do
  -- The plugin lowers REC into flat array construction:
  let user = REC { name = "Alice", score = 100 }
  putStrLn ("User: " ++ user.name)

  -- The plugin solves REC_UPD into O(1) setField without parentheses:
  let updated = REC_UPD user { score = 150 }
  print updated.score

Features

• Literal Offset Resolution: Solves FieldIndex @"foo" r directly to integer slot literals.
• Literal Tag Resolution: Solves ConstructorIndex @"Bar" s directly to integer constructor tags.
• Unrolled Core Synthesis: Direct code generation for record equality (RowEq) and formatting (RowShow).
• Human-Centric Error Diagnostics: Custom TypeError reporting with Levenshtein-distance fuzzy field name suggestions when fields or constructors are missing.
• Cross-GHC Support: Supports GHC 9.6 through GHC 9.14 via internal compatibility shims.

Documentation & Repository

• Main Repository: https://github.com/NadiaYvette/polytropos
• Plugin Architecture: PLUGIN_INVARIANTS.md

License

Dual-licensed under EUPL-1.2 OR Apache-2.0.