2016 Update

Task/List-comprehensions/JavaScript/list-comprehensions-1.js

@@ -1,14 +1,32 @@
-function range(begin, end) {
-    for (let i = begin; i < end; ++i)
-        yield i;
-}
+// USING A LIST MONAD DIRECTLY, WITHOUT SPECIAL SYNTAX FOR LIST COMPREHENSIONS
 
-function triples(n) {
-    return [[x,y,z] for each (x in range(1,n+1))
-                     for each (y in range(x,n+1))
-                     for each (z in range(y,n+1))
-                     if (x*x + y*y == z*z) ]
-}
+(function (n) {
 
-for each (var triple in triples(20))
-    print(triple);
+    return mb(r(1,     n), function (x) {  // x <- [1..n]
+    return mb(r(1 + x, n), function (y) {  // y <- [1+x..n]
+    return mb(r(1 + y, n), function (z) {  // z <- [1+y..n]
+
+       return x * x + y * y === z * z ? [[x, y, z]] : [];
+
+    })})});
+
+
+    // LIBRARY FUNCTIONS
+
+    // Monadic bind for lists
+    function mb(xs, f) {
+        return [].concat.apply([], xs.map(f));
+    }
+
+    // Monadic return for lists is simply lambda x -> [x]
+    // as in [[x, y, z]] : [] above
+
+    // Integer range [m..n]
+    function r(m, n) {
+        return Array.apply(null, Array(n - m + 1))
+            .map(function (n, x) {
+                return m + x;
+            });
+    }
+
+})(100);

Task/List-comprehensions/JavaScript/list-comprehensions-2.js

@@ -1,31 +1,14 @@
-(function(n) {
+function range(begin, end) {
+    for (let i = begin; i < end; ++i)
+        yield i;
+}
 
-  // USING A LIST MONAD DIRECTLY, WITHOUT LIST COMPREHENSION NOTATION
+function triples(n) {
+    return [[x,y,z] for each (x in range(1,n+1))
+                     for each (y in range(x,n+1))
+                     for each (z in range(y,n+1))
+                     if (x*x + y*y == z*z) ]
+}
 
-  return mb( rng(1,     n), function(x) {
-  return mb( rng(1 + x, n), function(y) {
-  return mb( rng(1 + y, n), function(z) {
-
-  return ( x * x + y * y === z * z ) ? mReturn([x, y, z]) : [];
-
-  })})});
-
-  /******************************************************************/
-
-  // Monadic bind (chain) for lists
-  function mb(xs, f) {
-    return [].concat.apply([], xs.map(f));
-  }
-
-  // Monadic return (inject) for lists
-  function mReturn(a) {
-    return [a];
-  }
-
-  function rng(m, n) {
-    return Array.apply(null, Array(n - m + 1)).map(
-      function (x, i) { return m + i; }
-    );
-  }
-
-})(100);
+for each (var triple in triples(20))
+    print(triple);

Task/List-comprehensions/JavaScript/list-comprehensions-3.js

@@ -0,0 +1,18 @@
+ (n => {
+
+     let flatMap = (xs, f) => [].concat.apply([], xs.map(f)),
+
+         range = (m, n) => Array.from({
+             length: (n - m) + 1
+         }, (_, i) => m + i);
+
+
+     return flatMap(range(1,     n), (x) =>
+            flatMap(range(1 + x, n), (y) =>
+            flatMap(range(1 + y, n), (z) =>
+                 x * x + y * y === z * z ? [
+                     [x, y, z]
+                 ] : []
+             )));
+
+ })(20);