aaronlevin

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aaronlevin

--title Rapid Prototyping in Haskell with Free Monads
--author Aaron Levin
--date today
--footer aaron levin (c) 2015 @ Bento Miso
--newpage

--center who?

* Aaron Levin
---

aaronlevin

-- | check for parens in a string, exiting early if the left paren count is -1. Fully point-free and
--   arrow-fied
-- It works as follows:
-- 1. use a monadic fold (foldM) with the Either monad to exit early
-- 2. take a list of methods that test if the count is -1, or the paren is '(', or the paren is ')'
-- 3. zip the list with another list that looks at the booleans and decides what functions they should 
--    result in. if there are no parens, the functions just add 0 to the count 
-- 4. sequence the monad actions (this will exit early if there is a Left present)
-- 5. fold over the functions in the Right branch with function composition 
-- 6. at this piont we just want to apply the the resulting function in the Right branch to the current

aaronlevin

module Fun where

import Control.Arrow ((<<<), (***))
import Data.Matrix (getElem, mapCol, mapRow, Matrix, setElem, zero)
import Data.List (foldl')

-- | initialize the edit-distance matrix.
-- λ> initEditMatrix "sitting" "kitten"
-- ( 0 1 2 3 4 5 6 )
-- ( 1 0 0 0 0 0 0 )

aaronlevin

{-| we often have this problem wehere we get some data
from the database that refers to another piece of data.
For example, suppose we have an Order that referes to 
a Customer and some Products. Do we represent it like this:

data Order = Order Customer [Product]

Or do we represent it like this:

data Order = Order UUID [UUID]

aaronlevin

{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE OverlappingInstances #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}

aaronlevin

# Inspired by: 
# http://stackoverflow.com/questions/29033580/how-do-i-use-the-new-haskell-ng-infrastructure-on-nixos
#
# The goal
#
# 1. my-project.cabal remains the source of required libraries/packages to build the project.
# Adding a new library involves updating my-project.cabal and then running cabal2nix . > 02-my-project.nix
#
# 2. ability to add non-haskell build / dev dependencies to our `shell.nix` that are not used at runtime.
# For example, maybe we want to use postgresql or redis during development.

aaronlevin

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}

module Foo where

import Prelude hiding (Bool(..), not)

aaronlevin

{-# LANGUAGE OverloadedStrings #-}

module SimpleThings where

import Control.Applicative ((<$>), (<*>))
import Control.Monad (mzero)
import Data.Aeson
import qualified Data.Aeson as A

-- | sum type containing all possible payloads

aaronlevin

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE TypeFamilies #-}

module GADTS where

-- Some universe of types
data Universe = A
              | B