benkolera

{ nixpkgs ? import <nixpkgs> {} }:
with nixpkgs.lib; with builtins;
let 
  gosub = (parents: subpath: type: 
    let path = "${parents}/${subpath}";
    in 
      if type == "directory" 
      then allKakFiles path
      else if type == "regular" && hasSuffix ".kak" subpath then [path]
      else [] 

benkolera

Note: This article requires you to understand basic haskell syntax, typeclasses and Functor/Applicative/Monad already. If you don't already understand these, this may be a struggle to understand.

---

Nested Monads aren't very fun

When writing monadic code, we can get ourselves into awkward circumstances where we have monads inside monads. Take for instance this code:

data OurErrors = OutputFileAlreadyExists | ParseFailure deriving (Eq, Show)

benkolera

frontend :: Frontend (R FrontendRoute)
frontend = Frontend
  { _frontend_head = el "title" $ text "Obelisk Minimal Example"
  , _frontend_body = prerender_ blank $ do
      i <- inputElement def
      t <- throttle 2 (_inputElement_input i)
      d <- debounce 2 (_inputElement_input i)
      tD <- holdDyn "" t
      dD <- holdDyn "" d
      text "throttled("

benkolera

Our web applications are getting increasingly more complicated. They are becoming more distributed and increasingly powered by combinations of complex, constantly changing and large datasets. All while users are increasingly more connected and want the latest information instantly without any slow page loads or stale information.

To address this, developers have turned to layers of caching and single page applications so that there are layers of aggregated and preloaded state as close to the user as possible, to be immediately available when it is requested. This comes at a high cost: it is very difficult to invalidate or update those caches when the upstream information changes. This is especially problematic when the stale caches can accidentally cause real bugs rather than show stale data to users.

The big issue here is that we're not just caching expensive-to-compute static data. We are caching data that changes over time. There are a number of architectual patterns that can be applied, but to date, n

benkolera

nix-shell -p '(import <nixos-1903> {}).pkgs.haskell.compiler.ghcjs84' -p 'haskell.packages.ghc864.ghcWithPackages(ps: [ps.zlib ps.HsOpenSSL])' -p cabal-install -p pkg-config -p brotli -p zlib -p zlib.dev -p postgresql -p openssl -p haskellPackages.happy

benkolera

diff --git a/src-ui.v3/src/API.hs b/src-ui.v3/src/API.hs
index d93e209..cae595d 100644
--- a/src-ui.v3/src/API.hs
+++ b/src-ui.v3/src/API.hs
@@ -7,6 +7,7 @@
 {-# LANGUAGE KindSignatures      #-}
 {-# LANGUAGE LambdaCase          #-}
 {-# LANGUAGE OverloadedStrings   #-}
+{-# LANGUAGE NoMonomorphismRestriction   #-}
 -- {-# LANGUAGE PolyKinds         #-}

benkolera

getV2IdxStates' :: Event t () -> m (Event t (ReqResult () PkgIdxTs))
getV2Info' :: Event t () -> m (Event t (ReqResult () ControllerInfo))
getV2Packages' :: Event t () -> m (Event t (ReqResult () (Vector PkgN)))
getV2PackagesHistory' :: Dynamic t (QParam PkgIdxTs) -> Dynamic t (QParam PkgIdxTs) -> Event t () -> m (Event t (ReqResult () (Vector IdxHistoryEntry)))
getV2PackageHistory' :: Dynamic t (Either Text PkgN) -> Event t () -> m (Event t (ReqResult () (Vector PkgHistoryEntry)))
getV2PackageReports' :: Dynamic t (Either Text PkgN)  -> Event t () -> m (Event t (ReqResult () (Set PkgIdxTs)))
getV2PackageReportSummary' :: Dynamic t (Either Text PkgN) -> Dynamic t (Either Text PkgIdxTs) -> Event t () -> m (Event t (ReqResult () PkgIdxTsReport))
getV2PackageReportDetail' :: Dynamic t (Either Text PkgN) -> Dynamic t (Either Text PkgIdxTs) -> Dynamic t (Either Text Ver) -> Dynamic t (Either Text CompilerID) -> Event t () -> m (Event t (ReqResult () CellReportDetail))
getV2PackageTags' :: Dynamic t (Either Text Pk

benkolera

Error: Found a project at ., but had to traverse one or more insecure directories to get there:
.obelisk/impl
.obelisk
.

Please ensure that all of these directories are owned by you and are not writable by anyone else.

unpacking 'https://github.com/NixOS/nixpkgs/archive/2d656a9729739e8ca5486058a76669d0ea4442df.tar.gz'...
copying path '/nix/store/s22136cyrw0lghy59m8bjkjkgar0cf3n-cabal2nix-backend' from 'https://nixcache.reflex-frp.org'...
copying path '/nix/store/4nbcjv2z4qham9jxp4q5d72yj1r32vh4-cabal2nix-common' from 'https://nixcache.reflex-frp.org'...

benkolera

{-# LANGUAGE DataKinds         #-}
{-# LANGUAGE FlexibleContexts  #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RankNTypes        #-}
{-# LANGUAGE TupleSections     #-}
{-# LANGUAGE TypeFamilies      #-}
module Obelisk.Servant where

import           Control.Concurrent.MVar (newEmptyMVar, putMVar, takeMVar)
import           Data.Bifunctor          (bimap)

benkolera

{-# LANGUAGE EmptyCase #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE EmptyCase #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleInstances #-}