MichaelBaker

What

A technique for writing parsers.

Why

• Easy to understand
• Generally applicable
• Full power of the programming language at your disposal
• Declarative

MichaelBaker

~/Projects/mrcss
( master )☛  time npm test

> mrcss@1.0.0 test /Users/michaeltbaker/Projects/mrcss
> mocha --compilers js:babel-core/register test/*



  Hello test
    1) does a thing

MichaelBaker

warning: there are multiple derivations named ‘nodejs-0.12.0’; using the first one
installing ‘nodejs-0.12.0’
these derivations will be built:
  /nix/store/8ap1vgh9979cl8p4b3c4xl3r8nqs1iid-nodejs-0.12.0.drv
building path(s) ‘/nix/store/pv1l6a2dqwfy41ldnpvgp1i7arzfvkqr-nodejs-0.12.0’
unpacking sources
unpacking source archive /nix/store/846c6d0zaqpg50ph7h6vba3fgdprcmqj-node-v0.12.0.tar.gz
source root is node-v0.12.0
patching sources
applying patch /nix/store/w9f0cqmzjgpdcyfqaihzf80bdwn7x4xg-no-xcode.patch

MichaelBaker

26       client.authorization = Signet::OAuth2::Client.new(
27         :token_credential_uri => 'https://www.googleapis.com/oauth2/v3/token',
28         :audience             => 'https://www.googleapis.com/oauth2/v3/token',
29         :scope                => scope,
30         :issuer               => GMAIL_ISSUER,
31         :signing_key          => key,
32         :person               => employee_email_address,
33       )

MichaelBaker

/*
data Creator = Stylist Int
             | Member Int
             | Service

data Service = Service1
             | Service2
*/

select * from outfits where creator = (Stylist _);

MichaelBaker

{-# LANGUAGE NoMonomorphismRestriction #-}

class Symantics r where
  int  :: Int -> r Int
  bool :: Bool -> r Bool
  add  :: r Int -> r Int -> r Int
  mul  :: r Int -> r Int -> r Int
  leq  :: r Int -> r Int -> r Bool
  if_  :: r Bool -> r a -> r a -> r a
  app  :: r (a -> b) -> r a -> r b

MichaelBaker

I'm experimenting with some ideas and I think one of the problems I have could be solved with lenses, but it doesn't seem to work how I expect it to when I try to implement it.

I want to create a tree of data structures, where each node stores a lens that goes from the root of the tree down to that node. Here is a conceptual image. The idea in that image is that the color of the lens matches the color of the path that it represents through the tree.

Here is an example of a tree shaped data structure without storing the path lenses at the nodes:

{-# LANGUAGE TemplateHaskell #-}

MichaelBaker

import Control.Monad.Reader (runReader, ask)

data Game = Game { playerOne    :: String
                 , playerTwo    :: String
                 , currentValue :: Int
                 }

data Move = Move { player :: String
                 , value  :: Int
                 }

MichaelBaker

vertex   = "#version 110\n attribute vec3 position; void main() { gl_Position = vec4(position, 1.0); }"
fragment = "#version 110\n void main() { gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); } "
time     = Monotonic

tris = [Triangle 0 0 0 (cos x) (sin x) 0 (cos (x^2)) (sin (x^2)) 0 | x <- [0.0,0.08..2*pi]]
nums = zip tris [0..]
len  = length tris

main = do
  withBasicWindow windowWidth windowHeight "Metropolis" $ \window -> do

MichaelBaker

data Tree a         = EndNode  | Leaf | Node a (Tree a) (Tree a)
data FlatTree       = FlatLeaf | FlatNode                        deriving (Show)
data NumberedTree a = NumLeaf  | NumNode Integer                 deriving (Show)

instance (Show a) => Show (Tree a) where
  show = showTreeIndented 0
    where showTreeIndented indentation Leaf                    = concat (take indentation $ repeat "  ") ++ "[]\n"
          showTreeIndented indentation (Node value left right) = concat (take indentation $ repeat "  ") ++ (show value) ++ "\n" ++ showTreeIndented (indentation + 1) left ++ showTreeIndented (indentation + 1) right