// Package expression parses and evaluates the expression language that is used in objects {{a.b[c]}} and tag parameters {%assign pages = site.pages | reverse%}. package expression import ( "github.com/osteele/liquid/generics" ) // Expression is a parsed expression. type Expression interface { // Evaluate evaluates an expression in a context. Evaluate(ctx Context) (interface{}, error) } // Closure binds an environment. type Closure interface { Bind(name string, value interface{}) Closure Evaluate() (interface{}, error) } type closure struct { expr Expression context Context } func (c closure) Bind(name string, value interface{}) Closure { // TODO create a new context c.context.Set(name, value) return c } func (c closure) Evaluate() (interface{}, error) { return c.expr.Evaluate(c.context) } type expression struct { evaluator func(Context) interface{} } func (e expression) Evaluate(ctx Context) (out interface{}, err error) { defer func() { if r := recover(); r != nil { switch e := r.(type) { case generics.GenericError: err = e case InterpreterError: err = e case UndefinedFilter: err = e default: panic(r) } } }() return e.evaluator(ctx), nil }