More example code in readme

README.md

@@ -15,25 +15,42 @@ Validates callback signatures against a prototype.
 // Create a prototype function (can be any callable)
 $prototype = function (A $a, B $b, $c): ?string {};
 
-// Create a type from the prototype
-$type = CallbackType::createFromCallable($prototype);
-
 // Validate that callables match the prototype
 $tests = [
     $prototype, // true
     function (A $a, B $b, $c) {}, // false - return type does not match
     function ($a, $b, $c): ?string {}, // true - arguments are contravariant
     function (A $a, B $b): ?string {}, // true - extra args don't cause errors
+    function (A $a, B $b, $c, $d): ?string {}, // false - Insufficient args cause an error
     function (C $a, B $b, $c): ?string {}, // true if C is a supertype of A, false otherwise
-    function (A $a, B $b, $c): string {}, // true, return types are covariant
+    function (SuperTypeOfA $a, B $b, $c): ?string {}, // true
+    function (A $a, B $b, $c): string {}, // true - return types are covariant
 ];
 
-foreach ($tests as $test) {
-    if ($type->isSatisfiedBy($test)) {
-        echo "pass\n";
-    } else {
-        // CallbackType implements __toString() for easy inspections
-        echo CallbackType::createFromCallable($test) . " does not satisfy $type\n";
+// Create a type from a prototype
+$type = CallbackType::createFromCallable($prototype);
+
+run_tests($type, $tests);
+
+// ...or create a type by hand for more granular control over variance rules
+$type = new CallbackType(
+    new ReturnType(BuiltInTypes::STRING, ReturnType::NULLABLE | ReturnType::COVARIANT),
+    new ParameterType('a', A::class),
+    new ParameterType('b', B::class),
+    new ParameterType('c')
+);
+
+run_tests($type, $tests);
+
+function run_tests(CallbackType $type, array $tests)
+{
+    foreach ($tests as $test) {
+        if ($type->isSatisfiedBy($test)) {
+            echo "pass\n";
+        } else {
+            // CallbackType implements __toString() for easy inspections
+            echo CallbackType::createFromCallable($test) . " does not satisfy {$type}\n";
+        }
     }
 }
 ```