Added support of using keywords in namespaces (#481)

* Added support of using keywords in namespaces

* Added true and false

* Removed unnecessary string case

pkg/compiler/compiler_func_ns_test.go

@@ -2,6 +2,7 @@ package compiler_test
 
 import (
 	"context"
+	"fmt"
 	"github.com/MontFerret/ferret/pkg/compiler"
 	"github.com/MontFerret/ferret/pkg/runtime/core"
 	"github.com/MontFerret/ferret/pkg/runtime/values"
@@ -78,4 +79,74 @@ func TestFunctionNSCall(t *testing.T) {
 
 		So(err, ShouldNotBeNil)
 	})
+
+	Convey("Should use keywords", t, func() {
+		c := compiler.New()
+
+		keywords := []string{
+			"And",
+			"Or",
+			"For",
+			"Return",
+			"Distinct",
+			"Filter",
+			"Sort",
+			"Limit",
+			"Let",
+			"Collect",
+			"Desc",
+			"Asc",
+			"None",
+			"Null",
+			"True",
+			"False",
+			"Use",
+			"Into",
+			"Keep",
+			"With",
+			"Count",
+			"All",
+			"Any",
+			"Aggregate",
+			"Like",
+			"Not",
+			"In",
+		}
+
+		for _, kw := range keywords {
+			segment := kw
+			err := c.Namespace("T").Namespace(segment).RegisterFunction("TEST", func(ctx context.Context, args ...core.Value) (core.Value, error) {
+				return values.True, nil
+			})
+
+			So(err, ShouldBeNil)
+
+			err = c.Namespace("T").Namespace(segment).RegisterFunction(segment, func(ctx context.Context, args ...core.Value) (core.Value, error) {
+				return values.True, nil
+			})
+
+			So(err, ShouldBeNil)
+
+			p, err := c.Compile(fmt.Sprintf(`
+			RETURN T::%s::TEST()
+		`, segment))
+
+			So(err, ShouldBeNil)
+
+			out := p.MustRun(context.Background())
+
+			So(string(out), ShouldEqual, "true")
+
+			p, err = c.Compile(fmt.Sprintf(`
+			RETURN T::%s::%s()
+		`, segment, segment))
+
+			So(err, ShouldBeNil)
+
+			out = p.MustRun(context.Background())
+
+			So(string(out), ShouldEqual, "true")
+		}
+	})
+
 }