September Morn Update

Task/Amb/JavaScript/amb-2.js

@@ -0,0 +1,55 @@
+(() => {
+    'use strict';
+
+    // amb :: [a] -> (a -> [b]) -> [b]
+    const amb = xs => f =>
+        xs.reduce((a, x) => a.concat(f(x)), []);
+
+    // when :: Bool -> [a] -> [a]
+    const when = p =>
+        xs => p ? (
+            xs
+        ) : [];
+
+
+    // TEST -----------------------------------------------
+    const main = () => {
+
+        // joins :: String -> String -> Bool
+        const joins = (a, b) =>
+            b[0] === last(a);
+
+        console.log(
+            amb(['the', 'that', 'a'])
+            (w1 => when(true)(
+
+                amb(['frog', 'elephant', 'thing'])
+                (w2 => when(joins(w1, w2))(
+
+                    amb(['walked', 'treaded', 'grows'])
+                    (w3 => when(joins(w2, w3))(
+
+                        amb(['slowly', 'quickly'])
+                        (w4 => when(joins(w3, w4))(
+
+                            unwords([w1, w2, w3, w4])
+
+                        ))
+                    ))
+                ))
+            ))
+        );
+    };
+
+    // GENERIC FUNCTIONS ----------------------------------
+
+    // last :: [a] -> a
+    const last = xs =>
+        0 < xs.length ? xs.slice(-1)[0] : undefined;
+
+    // unwords :: [String] -> String
+    const unwords = xs => xs.join(' ');
+
+    // MAIN ---
+    return main();
+})();