add graphql

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

graphql/callstack.go

@@ -0,0 +1,32 @@
+package generator
+
+type Callstack interface {
+	Push(entry interface{})
+	Pop(entry interface{})
+	Has(entry interface{}) bool
+}
+
+func NewCallstack() Callstack {
+	return &callstack{stack: make(map[interface{}]int), index: 0}
+}
+
+type callstack struct {
+	stack  map[interface{}]int
+	sorted []string
+	index  int
+}
+
+func (c *callstack) Pop(entry interface{}) {
+	delete(c.stack, entry)
+	c.index--
+}
+
+func (c *callstack) Push(entry interface{}) {
+	c.stack[entry] = c.index
+	c.index++
+}
+
+func (c *callstack) Has(entry interface{}) bool {
+	_, ok := c.stack[entry]
+	return ok
+}