Adding toJSON and toYAML functions

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

README.md

@@ -67,6 +67,10 @@ Gomplate is an alternative that will let you process templates which also includ
 				- [Example](#example)
 			- [`yamlArray`](#yamlarray)
 				- [Example](#example)
+			- [`toJSON`](#tojson)
+				- [Example](#example)
+			- [`toYAML`](#toyaml)
+				- [Example](#example)
 			- [`datasource`](#datasource)
 				- [Examples](#examples)
 					- [Basic usage](#basic-usage)
@@ -111,7 +115,7 @@ $ apk add gomplate
 ...
 ```
 
-_Note: the Alpine version of gomplate may lag behind the latest release of gomplate._ 
+_Note: the Alpine version of gomplate may lag behind the latest release of gomplate._
 
 ### use with Docker
 
@@ -453,6 +457,43 @@ $ gomplate < input.tmpl
 Hello world
 ```
 
+#### `toJSON`
+
+Converts an object to a JSON document. Input objects may be the result of `json`, `yaml`, `jsonArray`, or `yamlArray` functions, or they could be provided by a `datasource`.
+
+##### Example
+
+_This is obviously contrived - `json` is used to create an object._
+
+_`input.tmpl`:_
+```
+{{ ("{\"foo\":{\"hello\":\"world\"}}" | json).foo | toJSON }}
+```
+
+```console
+$ gomplate < input.tmpl
+{"hello":"world"}
+```
+
+#### `toYAML`
+
+Converts an object to a YAML document. Input objects may be the result of `json`, `yaml`, `jsonArray`, or `yamlArray` functions, or they could be provided by a `datasource`.
+
+##### Example
+
+_This is obviously contrived - `json` is used to create an object._
+
+_`input.tmpl`:_
+```
+{{ ("{\"foo\":{\"hello\":\"world\"}}" | json).foo | toYAML }}
+```
+
+```console
+$ gomplate < input.tmpl
+hello: world
+
+```
+
 #### `datasource`
 
 Parses a given datasource (provided by the [`--datasource/-d`](#--datasource-d) argument).

main.go

@@ -56,6 +56,8 @@ func NewGomplate(data *Data) *Gomplate {
 			"yamlArray":        typeconv.YAMLArray,
 			"slice":            typeconv.Slice,
 			"join":             typeconv.Join,
+			"toJSON":           typeconv.ToJSON,
+			"toYAML":           typeconv.ToYAML,
 			"ec2meta":          ec2meta.Meta,
 			"ec2dynamic":       ec2meta.Dynamic,
 			"ec2tag":           ec2info.Tag,

typeconv.go

@@ -64,6 +64,25 @@ func (t *TypeConv) YAMLArray(in string) []interface{} {
 	return unmarshalArray(obj, in, yaml.Unmarshal)
 }
 
+func marshalObj(obj interface{}, f func(interface{}) ([]byte, error)) string {
+	b, err := f(obj)
+	if err != nil {
+		log.Fatalf("Unable to marshal object %s: %v", obj, err)
+	}
+
+	return string(b)
+}
+
+// ToJSON - Stringify a struct as JSON
+func (t *TypeConv) ToJSON(in interface{}) string {
+	return marshalObj(in, json.Marshal)
+}
+
+// ToYAML - Stringify a struct as YAML
+func (t *TypeConv) ToYAML(in interface{}) string {
+	return marshalObj(in, yaml.Marshal)
+}
+
 // Slice creates a slice from a bunch of arguments
 func (t *TypeConv) Slice(args ...interface{}) []interface{} {
 	return args

typeconv_test.go

@@ -59,6 +59,31 @@ func TestUnmarshalArray(t *testing.T) {
 `))
 }
 
+func TestToJSON(t *testing.T) {
+	ty := new(TypeConv)
+	expected := `{"foo":"bar","one":1,"true":true}`
+	in := map[string]interface{}{
+		"foo":  "bar",
+		"one":  1,
+		"true": true,
+	}
+	assert.Equal(t, expected, ty.ToJSON(in))
+}
+
+func TestToYAML(t *testing.T) {
+	ty := new(TypeConv)
+	expected := `foo: bar
+one: 1
+"true": true
+`
+	in := map[string]interface{}{
+		"foo":  "bar",
+		"one":  1,
+		"true": true,
+	}
+	assert.Equal(t, expected, ty.ToYAML(in))
+}
+
 func TestSlice(t *testing.T) {
 	ty := new(TypeConv)
 	expected := []string{"foo", "bar"}