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garybgaryb
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Merge pull request #2 from purescript/0.8-updates
Updates for PureScript 0.8
2 parents f41e713 + 2de0414 commit 6830dde

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‎.jscsrc

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{
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"preset": "grunt",
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"disallowSpacesInFunctionExpression": null,
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"requireSpacesInFunctionExpression": {
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"beforeOpeningRoundBrace": true,
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"beforeOpeningCurlyBrace": true
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},
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"disallowSpacesInAnonymousFunctionExpression": null,
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"requireSpacesInAnonymousFunctionExpression": {
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"beforeOpeningRoundBrace": true,

‎.jshintrc

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"freeze": true,
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"funcscope": true,
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"futurehostile": true,
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"globalstrict": true,
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"strict": "global",
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"latedef": true,
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"maxparams": 1,
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"noarg": true,
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"singleGroups": true,
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"undef": true,
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"unused": true,
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"eqnull": true
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"eqnull": true,
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"predef": ["exports"]
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}

‎.travis.yml

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language: node_js
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sudo: false
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node_js:
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- 0.10
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sudo: required
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dist: trusty
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node_js: 5
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env:
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- PATH=$HOME/purescript:$PATH
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install:
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- TAG=$(wget -q -O - https://github.com/purescript/purescript/releases/latest --server-response --max-redirect 0 2>&1 | sed -n -e 's/.*Location:.*tag\///p')
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- wget -O $HOME/purescript.tar.gz https://github.com/purescript/purescript/releases/download/$TAG/linux64.tar.gz
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- tar -xvf $HOME/purescript.tar.gz -C $HOME/
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- chmod a+x $HOME/purescript
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- npm install -g bower
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- npm install
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- bower install
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script:
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- npm run build
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- npm test
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after_success:
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- >-
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test $TRAVIS_TAG &&
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psc-publish > .pursuit.json &&
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curl -X POST http://pursuit.purescript.org/packages \
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-d @.pursuit.json \
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-H 'Accept: application/json' \
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-H "Authorization: token ${GITHUB_TOKEN}"

‎README.md

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[![Build Status](https://travis-ci.org/purescript/purescript-exists.svg?branch=master)](https://travis-ci.org/purescript/purescript-exists)
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[![Dependency Status](https://www.versioneye.com/user/projects/55848c7c363861001d000339/badge.svg?style=flat)](https://www.versioneye.com/user/projects/55848c7c363861001d000339)
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Existential types as a library.
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The `Exists` type, for encoding existential types.
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## Installation
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```
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bower install purescript-exists
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```
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## Module documentation
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## Overview
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- [Data.Exists](docs/Data/Exists.md)
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The type `Exists f` is isomorphic to the existential type `exists a. f a`.
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For example, consider the type `exists s. Tuple s (s -> Tuple s a)` which represents infinite streams of elements of type `a`.
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This type can be constructed by creating a type constructor `StreamF` as follows:
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```purescript
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data StreamF a s = StreamF s (s -> Tuple s a)
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```
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We can then define the type of streams using `Exists`:
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```purescript
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type Stream a = Exists (StreamF a)
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```
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The `mkExists` and `runExists` functions then enable packing and unpacking of `SteamF` into/out of `Stream`.
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## Documentation
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Module documentation is [published on Pursuit](http://pursuit.purescript.org/packages/purescript-exists).

‎bower.json

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{
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"name": "purescript-exists",
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"homepage": "https://github.com/purescript/purescript-exists",
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"description": "Existential types as a library",
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"keywords": ["purescript"],
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"license": "MIT",
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"repository": {
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"type": "git",
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"bower.json",
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"package.json"
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],
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"dependencies": {
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"purescript-unsafe-coerce": "^1.0.0-rc.1"
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},
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"devDependencies": {
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"purescript-console": "^0.1.0"
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"purescript-console": "^1.0.0-rc.1"
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}
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}

‎docs/Data/Exists.md

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‎package.json

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{
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"private": true,
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"scripts": {
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"postinstall": "pulp dep install",
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"build": "jshint src && jscs src && pulp test && rimraf docs && pulp docs"
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"clean": "rimraf output && rimraf .pulp-cache",
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"build": "jshint src && jscs src && pulp build",
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"test": "jshint src && jscs src && pulp test"
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},
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"devDependencies": {
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"jscs": "^1.13.1",
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"jshint": "^2.8.0",
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"pulp": "^4.0.2",
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"rimraf": "^2.4.1"
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"jscs": "^2.8.0",
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"jshint": "^2.9.1",
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"pulp": "^8.1.0",
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"rimraf": "^2.5.0"
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}
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}

‎src/Data/Exists.js

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‎src/Data/Exists.purs

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module Data.Exists where
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import Prelude
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import Unsafe.Coerce (unsafeCoerce)
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-- | This type constructor can be used to existentially quantify over a type of kind `*`.
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-- |
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-- | This type can be constructed by creating a type constructor `StreamF` as follows:
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-- |
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-- | ```purescript
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-- | data StreamF a s = StreamF s (s -> Tuple s a)
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-- | data StreamF a s = StreamF s (s -> Tuple s a)
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-- | ```
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-- |
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-- | We can then define the type of streams using `Exists`:
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-- | nats :: Stream Number
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-- | nats = mkExists $ StreamF 0 (\n -> Tuple (n + 1) n)
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-- | ```
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foreign import mkExists :: forall f a. f a -> Exists f
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mkExists :: forall f a. f a -> Exists f
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mkExists = unsafeCoerce
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-- | The `runExists` function is used to eliminate a value of type `Exists f`. The rank 2 type ensures
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-- | that the existentially-quantified type does not escape its scope. Since the function is required
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-- | to work for _any_ type `a`, it will work for the existentially-quantified type.
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-- |
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-- |
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-- | For example, we can write a function to obtain the head of a stream by using `runExists` as follows:
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-- |
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-- | ```purescript
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-- | head :: forall a. Stream a -> a
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-- | head = runExists head'
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-- | where
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-- | head' :: forall s. StreamF a s -> a
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-- | head' (StreamF s f) = snd (f s)
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-- | head' (StreamF s f) = snd (f s)
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-- | ```
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foreign import runExists :: forall f r. (forall a. f a -> r) -> Exists f -> r
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runExists :: forall f r. (forall a. f a -> r) -> Exists f -> r
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runExists = unsafeCoerce

‎test/Test/Main.purs

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import Prelude
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import Control.Monad.Eff.Console
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import Data.Exists
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import Control.Monad.Eff (Eff)
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import Control.Monad.Eff.Console (CONSOLE, logShow)
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import Data.Exists (Exists, mkExists, runExists)
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data Tuple a b = Tuple a b
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head' :: forall s. StreamF a s -> a
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head' (StreamF s f) = snd (f s)
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main = print $ head nats
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main :: Eff (console :: CONSOLE) Unit
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main = logShow $ head nats

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