fix handling of infinite generators by tail

Author: make-github-pseudonymous-again

src/base/frame.js

@@ -19,8 +19,8 @@ export function* frame ( iterable , n ) {
 
 	// Could have an implementation using a deque
 	// that doesn't slice (and thus allocate a new
-	// vector everytime). Though the yieded object
-	// cannot be modified by the caller in this case.
+	// vector everytime). Though the yield object
+	// could not be modified by the caller in that case.
 
 	const iterator = iter( iterable ) ;
 

src/base/tail.js

@@ -14,9 +14,12 @@ import { drop } from './drop' ;
  * @param {Number} n - The number of elements to include in the output.
  * @returns {Array} - The last <code>n</code> elements of the input iterable.
  */
-export function tail ( iterable , n ) {
+export function* tail ( iterable , n ) {
 
-	if ( n < 0 ) return drop( iterable , -n ) ;
+	if ( n < 0 ) {
+		yield* drop( iterable , -n ) ;
+		return ;
+	}
 
 	const iterator = iter( iterable ) ;
 
@@ -25,7 +28,10 @@ export function tail ( iterable , n ) {
 
 	while ( n --> 0 ) {
 		const e = iterator.next( ) ;
-		if ( e.done ) return buffer ;
+		if ( e.done ) {
+			yield* buffer ;
+			return ;
+		}
 		buffer.push( e.value ) ;
 	}
 
@@ -34,6 +40,6 @@ export function tail ( iterable , n ) {
 		buffer.shift() ;
 	}
 
-	return buffer ;
+	yield* buffer ;
 
 }

test/src/base/tail.js

@@ -1,6 +1,6 @@
 import test from 'ava' ;
 
-import { range , tail , list } from '../../..' ;
+import { range , tail , list , count } from '../../..' ;
 
 test( "tail" , t => {
 
@@ -11,3 +11,9 @@ test( "tail" , t => {
 	t.deepEqual( list( tail( range( 100 ) , 1000 ) ) , list( range( 100 ) ) ) ;
 
 } ) ;
+
+test( "construct tail of infinite generator" , t => {
+
+	tail( count( ) , 10 ) ;
+
+} ) ;