fix product function and add examples

examples/00_Hello_World.mers

@@ -0,0 +1 @@
+"Hello, World!".println

examples/01_Hello_Name.mers

@@ -0,0 +1,3 @@
+"What's you name?".println
+name := ().read_line.trim
+("Hello, ", name, "!").concat.println

examples/02_Calc_Sum.mers

@@ -0,0 +1,13 @@
+total := 0.0
+{() -> {
+  ("Total: ", total, ". Type a number to change.").concat.println
+  (
+    ().read_line.trim.parse_float,
+    (
+      n -> &total = (total, n).sum,
+      // not a number, so return a 1-tuple to break from the loop
+      () -> (())
+    )
+  ).try
+}}.loop
+"Goodbye.".println

examples/03_Basic_Calculator.mers

@@ -0,0 +1,30 @@
+"- Calculator -".println
+"Type =<num> to set the value to that number.".println
+"Type +<num>, -<num> or *<num> to change the value.".println
+"Type exit to exit.".println
+
+current := 0.0
+
+{() -> {
+  ("[ ", current, " ]").concat.println
+  input := ().read_line.trim
+  num := (
+    (input, 1).substring.trim.parse_float,
+    (
+      () -> 0.0,
+      val -> val
+    )
+  ).try
+  mode := (input, 0, 1).substring
+  if (mode, "+").eq {
+    &current = (current, num).sum
+  } else if (mode, "-").eq {
+    &current = (current, (num, -1).product).sum
+  } else if (mode, "*").eq {
+    &current = (current, num).product
+  } else if (mode, "=").eq {
+    &current = num
+  } else if (input, "exit").eq {
+    (())
+  }
+}}.loop