fix State definition (#11)

CHANGELOG.md

@@ -21,6 +21,9 @@
   - add NonEmptyArray, fix #12 (@gcanti)
 - **Polish**
   - add tslint
+- **Bug Fix**
+  - fix `State` definition (@gcanti)
+
 
 # 0.0.2
 

src/State.ts

@@ -20,13 +20,19 @@ export class State<S, A> implements HKTState<S, A> {
     return this.run(s)[1]
   }
   map<B>(f: Function1<A, B>): State<S, B> {
-    return new State<S, B>(s => [f(this.eval(s)), s])
+    return new State<S, B>(s => {
+      const [a, s1] = this.run(s)
+      return [f(a), s1]
+    })
   }
   ap<B>(fab: State<S, Function1<A, B>>): State<S, B> {
     return fab.chain(f => map(f, this)) // <= derived
   }
   chain<B>(f: Function1<A, State<S, B>>): State<S, B> {
-    return new State<S, B>(s => (f(this.eval(s))).run(s))
+    return new State<S, B>(s => {
+      const [a, s1] = this.run(s)
+      return f(a).run(s1)
+    })
   }
 }
 
@@ -59,7 +65,7 @@ export function modify<S>(f: Endomorphism<S>): State<S, void> {
 }
 
 export function gets<S, A>(f: Function1<S, A>): State<S, A> {
-  return get<S>().chain(s => of<S, A>(f(s)))
+  return new State<S, A>(s => [f(s), s])
 }
 
 // tslint:disable-next-line no-unused-expression

test/State.ts

@@ -0,0 +1,40 @@
+import * as assert from 'assert'
+import {
+  put,
+  get,
+  modify,
+  gets,
+  State
+} from '../src/State'
+
+describe('State', () => {
+  it('put', () => {
+    assert.deepEqual(put(2).run(1), [undefined, 2])
+  })
+
+  it('get', () => {
+    assert.deepEqual(get().run(1), [1, 1])
+  })
+
+  it('modify', () => {
+    const double = (n: number) => n * 2
+    assert.deepEqual(modify(double).run(1), [undefined, 2])
+  })
+
+  it('gets', () => {
+    const double = (n: number) => n * 2
+    assert.deepEqual(gets(double).run(1), [2, 1])
+  })
+
+  it('map', () => {
+    const double = (n: number) => n * 2
+    const state = new State<number, number>(s => [s - 1, s + 1])
+    assert.deepEqual(state.map(double).run(0), [-2, 1])
+  })
+
+  it('chain', () => {
+    const f = (n: number) => new State<number, number>(s => [s - 1, s + 1])
+    const state = new State<number, number>(s => [s - 1, s + 1])
+    assert.deepEqual(state.chain(f).run(0), [0, 2])
+  })
+})