tmcgilchrist

```
                                       OCaml compilation pipeline





                                            ┌────────────────┐
                                            │                │
                                            │  Source code   │

tmcgilchrist

{-# LANGUAGE ConstraintKinds       #-}
{-# LANGUAGE DeriveGeneric         #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE TemplateHaskell       #-}
{-# LANGUAGE TypeApplications      #-}
{-# LANGUAGE TypeFamilies          #-}

tmcgilchrist

Today we'll be looking into Kmett's
[adjunctions](http://hackage.haskell.org/package/adjunctions) library,
particularly the meat of the library in Data.Functor.Adjunction.

This post is a literate haskell file, which means you can load it right up in
ghci and play around with it! Like any good haskell file we need half a dozen
language pragmas and imports before we get started.

> {-# language DeriveFunctor #-}
> {-# language TypeFamilies #-}

tmcgilchrist

Releasing to Hackage

1. Create PR bumping version number
2. Ensure it's building on CI
3. Bump version in *.cabal file
4. Commit new version to repo and push
5. cabal sdist to generate a package
6. cabal upload dist/pkg-x.y.x.tar.gz
7. tag repo with this version
8. Upload haddock changes

tmcgilchrist

(eval-after-load "haskell-mode"
  ;; Replace the haskell-mode version with this version,
  ;; this will line up all imports as if they're all qualified
  ;; eg this
  ;;
  ;; import Data.Monoid
  ;; import Data.Text
  ;;
  ;; becomes
  ;;

tmcgilchrist

class Show a where
    show :: a -> String

instance Show Int where
    show = ... -- provided by default

show 1 

tmcgilchrist

General musing on some projects I'd like to try writing with OCaml

 - database bindings for MySQL that include proper type checking and embedding sql ala pgocaml
 - general application that queries webservice, does DB stuff and then does webservice requests (eg Antiquarian)
 - functor/monad/monoid library
 - bindings for libyaml 
 - bindings for https://github.com/joyent/libuv Cross platform async IO
 - library for connecting to Riak
 - lightwieght monadic regions implementation
 - property based testing library

tmcgilchrist

> cat ~/.sbt/0.13/plugins/plugins.sbt
resolvers += Resolver.sonatypeRepo("snapshots")

addSbtPlugin("org.ensime" % "ensime-sbt" % "0.1.5-SNAPSHOT")

> sbt gen-ensime
[info] Loading global plugins from /Users/tim/.sbt/0.13/plugins
[info] Loading project definition from /Users/tim/code/scala/introduction-to-fp-in-scala/project
[info] Set current project to introduction-to-fp-in-scala (in build file:/Users/tim/code/scala/introduction-to-fp-in-scala/)
[error] Not a valid command: gen-ensime

tmcgilchrist

```
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      | |-+-| | |-+-| | 
      | |_|_| | |_|_| | 

tmcgilchrist

module type Stack =
  sig
    type 'a t

    val empty   : 'a t
    val isEmpty : 'a t -> bool
    val cons    : 'a -> 'a t -> 'a t
    val head    : 'a t -> 'a
    val tail    : 'a t -> 'a t
  end