SelectMany

Formlets.CSharp.Tests/Usage.cs

@@ -170,5 +170,22 @@ join age in e.Int() on 1 equals 1
             Assert.Equal(42, r.Value.Value.age);
         }
 
+        [Fact]
+        public void LINQ_SelectMany() {
+            var e = new FormElements();
+            var f = from name in e.Text()
+                    from _ in Formlet.Raw(X.E("br"))
+                    from age in e.Int()
+                    where age == 42
+                    select new { name, age };
+            var r = f.Run(new Dictionary<string, string> {
+                {"f0", "John"},
+                {"f1", "42"},
+            });
+            Assert.True(r.Value.HasValue());
+            Assert.Equal("John", r.Value.Value.name);
+            Assert.Equal(42, r.Value.Value.age);
+        }
+
     }
 }

Formlets.CSharp/FormletT.cs

@@ -149,7 +149,18 @@ public Formlet<T> Where(Func<T,bool> pred) {
         }
 
         public Formlet<R> Join<I, K, R>(Formlet<I> inner, Func<T, K> outerKeySelector, Func<I, K> innerKeySelector, Func<T, I, R> resultSelector) {
-            return Formlet.Tuple2<T, I>().Ap(this).Ap(inner).Select(t => resultSelector(t.Item1, t.Item2));
+            return Formlet.Tuple2<T, I>()
+                .Ap(this)
+                .Ap(inner)
+                .Select(t => resultSelector(t.Item1, t.Item2));
+        }
+
+        public Formlet<R> SelectMany<R>(Func<Formlet<T>, Formlet<R>> collector) {
+            return collector(this);
+        }
+
+        public Formlet<R> SelectMany<U, R>(Func<Formlet<T>, Formlet<U>> collector, Func<T, U, R> selector) {
+            return this.Join<U,object,R>(collector(this), x => x, x => x, selector);
         }
 
         public Formlet<T> Satisfies(Func<T,bool> pred, Func<T, List<XNode>, IEnumerable<XNode>> error, Func<T, IEnumerable<string>> errorMsg) {