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package stick
import (
// A Template represents a named template and its contents.
type Template interface {
// Name returns the name of this Template.
Name() string
// Contents returns an io.Reader for reading the Template contents.
Contents() io.Reader
// A Func represents a user-defined function.
// Functions can be called anywhere expressions are allowed and
// take any number of arguments.
type Func func(ctx Context, args ...Value) Value
// A Filter is a user-defined filter.
// Filters receive a value and modify it in some way. Filters
// also accept parameters.
type Filter func(ctx Context, val Value, args ...Value) Value
// A Test represents a user-defined test.
// Tests are used to make some comparisons more expressive. Tests
// also accept arguments and can consist of two words.
type Test func(ctx Context, val Value, args ...Value) bool
// Env represents a configured Stick environment.
type Env struct {
Loader Loader // Template loader.
Functions map[string]Func // User-defined functions.
Filters map[string]Filter // User-defined filters.
Tests map[string]Test // User-defined tests.
Visitors []parse.NodeVisitor // User-defined node visitors.
// An Extension is used to group related functions, filters, visitors, etc.
type Extension interface {
// Init is the entry-point for an extension to modify the Env.
Init(*Env) error
// ContextMetadata contains additional, unstructured runtime attributes about
// the template being executed.
type ContextMetadata interface {
All() map[string]string // Returns a map of all attributes and values.
Set(name, val string) // Set a metadata attribute on the context.
Get(name string) (string, bool) // Get a metadata attribute on the context.
noexport() // Prevent other packages from satisfying this interface.
// ContextScope provides an interface with the currently executing template's
// scope.
type ContextScope interface {
All() map[string]Value // Returns a map of all values defined in the scope.
Get(string) (Value, bool) // Get a value defined in the scope.
Set(string, Value) // Set a value in the scope.
noexport() // Prevent other packages from satisfying this interface.
// A Context represents the execution context of a template.
// The Context is passed to all user-defined functions, filters, tests,
// and node visitors. It can be used to affect and inspect the local
// environment while a template is executing.
type Context interface {
Name() string // The name of the template being executed.
Meta() ContextMetadata // Runtime metadata about the template.
Scope() ContextScope // All defined root-level names.
Env() *Env
noexport() // Prevent other packages from satisfying this interface.
// New creates an empty Env.
// If nil is passed as loader, a StringLoader is used.
func New(loader Loader) *Env {
if loader == nil {
loader = &StringLoader{}
return &Env{loader, make(map[string]Func), make(map[string]Filter), make(map[string]Test), make([]parse.NodeVisitor, 0)}
// Register adds the given Extension to the Env.
func (env *Env) Register(e Extension) error {
return e.Init(env)
// Execute parses and executes the given template.
func (env *Env) Execute(tpl string, out io.Writer, ctx map[string]Value) error {
return execute(tpl, out, ctx, env)
// Parse loads and parses the given template.
func (env *Env) Parse(name string) (*parse.Tree, error) {
return env.load(name)