alpmestan

This file contains any messages produced by compilers while
running configure, to aid debugging if configure makes a mistake.

It was created by The Glorious Glasgow Haskell Compilation System configure 8.7, which was
generated by GNU Autoconf 2.69.  Invocation command line was

  $ ./configure --target=aarch64-unknown-linux-gnu

## --------- ##
## Platform. ##

alpmestan

Up to date
]0;Starting...| Run Cc FindCDependencies Stage1: rts/Linker.c => _build/stage1/rts/build/c/Linker.debug_dyn_o.d
| Run Cc FindCDependencies Stage1: rts/RaiseAsync.c => _build/stage1/rts/build/c/RaiseAsync.thr_o.d
| Run Cc FindCDependencies Stage1: rts/WSDeque.c => _build/stage1/rts/build/c/WSDeque.dyn_o.d
| Run Cc FindCDependencies Stage1: rts/sm/Scav_thr.c => _build/stage1/rts/build/c/sm/Scav_thr.thr_debug_o.d
| Run Cc FindCDependencies Stage1: rts/linker/elf_plt_aarch64.c => _build/stage1/rts/build/c/linker/elf_plt_aarch64.thr_dyn_o.d
| Run Cc FindCDependencies Stage1: rts/sm/Storage.c => _build/stage1/rts/build/c/sm/Storage.l_dyn_o.d
| Run Cc FindCDependencies Stage1: rts/Timer.c => _build/stage1/rts/build/c/Timer.thr_dyn_o.d
| Run Cc FindCDependencies Stage1: rts/Hash.c => _build/stage1/rts/build/c/Hash.thr_o.d
| Run Cc FindCDependencies Stage1: rts/RtsFlags.c => _build/stage1/rts/build/c/RtsFlags.o.d

alpmestan

{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE RecursiveDo #-}
{-# LANGUAGE DeriveFunctor #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
-- | A simple graph library
module Graph
  ( -- * Creating graphs
    runGraph
  , newGraph
  , node

alpmestan

{ pkgs ? import <nixpkgs> {}
, compiler ? "ghc822"
}:

with pkgs;

let
  ghc = haskell.packages.${compiler}.ghcWithPackages (ps: with ps; [ cabal-install ]);
in

alpmestan

---
title: Why is servant a type-level DSL?
author: Alp Mestanogullari
date: 2018-07-43 20:00
toc: true
---

---

This post is an attempt at explaining servant's design as an embedded domain

alpmestan

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE UndecidableInstances #-}

import Data.Proxy
import GHC.TypeLits
import Servant.API

alpmestan

type Flat api = Reassoc (Flatten api)

-- | Completely flattens an API type by applying a few simple transformations.
--   The goal is to end up with an aPI type where things like @a :> (b :<|> c)@
--   are rewritten to @a :> b :<|> a :> c@, so as to have client with very simple
--   types, instead of "nested clients".
type family Flatten (api :: k) :: k where
  Flatten ((a :: k) :> (b :<|> c)) = a :> Flatten b :<|> Flatten (a :> c)
  Flatten ((a :<|> b) :> c) = a :> Flatten c :<|> (Flatten (b :> c))
  Flatten ((a :: k) :> b)          = Redex b (Flatten b) a

alpmestan

{
  packageOverrides = ps: rec {
    haskell.compiler = ps.haskell.compiler // {
      myghc = ps.haskell.compiler.ghcHEAD.overrideDerivation (p: {
        src = fetchgit {
          url = "git://git.haskell.org/ghc.git";
          rev = "commit hash here";
          sha256 = "sha that nix computes for this";
        };
      });

alpmestan

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeOperators #-}
import Data.Proxy
import GHC.TypeLits
import Servant.API

infixr 9 >:>
infixr 8 <||>

alpmestan

{-
$ curl -X POST localhost:9876/dog -v
* Connected to localhost (127.0.0.1) port 9876 (#0)
> POST /dog HTTP/1.1
> Host: localhost:9876
> User-Agent: curl/7.55.1
> Accept: */*
> 
< HTTP/1.1 301 Moved Permanently
< Transfer-Encoding: chunked