trivial Lazy instance for functions (#38)

* trivial Lazy instance for functions

* make lazyFn defer actually defer fn call

Add tests for this.

* relax types in tests

Author: matthewleon

.travis.yml

@@ -11,9 +11,11 @@ install:
   - chmod a+x $HOME/purescript
   - npm install -g bower
   - npm install
-  - bower install
 script:
+  - bower install --production
   - npm run -s build
+  - bower install
+  - npm -s test
 after_success:
 - >-
   test $TRAVIS_TAG &&

bower.json

@@ -18,5 +18,8 @@
   ],
   "dependencies": {
     "purescript-prelude": "^3.0.0"
+  },
+  "devDependencies": {
+    "purescript-eff": "^3.1.0"
   }
 }

package.json

@@ -2,7 +2,8 @@
   "private": true,
   "scripts": {
     "clean": "rimraf output && rimraf .pulp-cache",
-    "build": "pulp build -- --censor-lib --strict"
+    "build": "pulp build -- --censor-lib --strict",
+    "test": "pulp test"
   },
   "devDependencies": {
     "pulp": "^10.0.4",

src/Control/Lazy.purs

@@ -1,6 +1,6 @@
 module Control.Lazy where
 
-import Data.Unit (Unit)
+import Data.Unit (Unit, unit)
 
 -- | The `Lazy` class represents types which allow evaluation of values
 -- | to be _deferred_.
@@ -10,6 +10,9 @@ import Data.Unit (Unit)
 class Lazy l where
   defer :: (Unit -> l) -> l
 
+instance lazyFn :: Lazy (a -> b) where
+  defer f = \x -> f unit x
+
 -- | `fix` defines a value as the fixed point of a function.
 -- |
 -- | The `Lazy` instance allows us to generate the result lazily.

test/Test/Control/Lazy.purs

@@ -0,0 +1,19 @@
+module Test.Control.Lazy (testLazy) where
+
+import Control.Applicative (pure)
+import Control.Monad.Eff (Eff)
+import Control.Lazy (fix)
+import Data.Unit (Unit, unit)
+
+foo :: forall a. a -> Unit
+foo _ = unit
+
+foofoo :: forall a b. a -> (b -> Unit)
+foofoo _ = foo
+
+foo' :: forall a. a -> Unit
+foo' = fix foofoo
+
+-- the idea here is that foo and foo' are the same function
+testLazy :: Eff () Unit
+testLazy = pure (foo' unit)

test/Test/Main.purs

@@ -0,0 +1,9 @@
+module Test.Main (main) where
+
+import Control.Monad.Eff (Eff)
+import Data.Unit (Unit)
+
+import Test.Control.Lazy (testLazy)
+
+main :: Eff () Unit
+main = testLazy