Go Interpreter (in 35 lines) - CURRENTLY NOT WORKING

interp.go

// NOT WORKING AS AT 14-JAN-14 DUE TO API CHANGES
//
// written for the Go London User Group meeting of 21st November 2013 by Elliott Stoneham
// uses code.google.com/p/go.tools/ssa/interp which warns “It is not, and will never be, a production-quality Go interpreter.”
// main() code adapted from the example given in code.google.com/p/go.tools/ssa
// requires go version 1.2 
//
package main

import (
	"code.google.com/p/go.tools/importer"
	"code.google.com/p/go.tools/ssa"
	"code.google.com/p/go.tools/ssa/interp"
	"fmt"
	"go/build"
	"go/parser"
)

const code = `
package main 		// example inspired by gobyexample.com/recursion
import 	_ "runtime"     // required by go.tools/ssa/interp
func fact(n int) int {
	if n == 0 {
		return 1
	}
	return n * fact(n-1)
}
func main() { println("ten factorial is ",fact(10)) }
`

func main() {
	imp := importer.New(&importer.Config{Build: &build.Default}) // Imports will be loaded as if by 'go build'.
	file, err := parser.ParseFile(imp.Fset, "main.go", code, 0)  // Parse the input file.
	if err != nil {
		fmt.Print(err) // parse error
		return
	}
	mainInfo := imp.CreatePackage("main", file) // Create single-file main package and import its dependencies.
	var mode ssa.BuilderMode
	prog := ssa.NewProgram(imp.Fset, mode) // Create SSA-form program representation.
	if err := prog.CreatePackages(imp); err != nil {
		fmt.Print(err) // type error in some package
		return
	}
	mainPkg := prog.Package(mainInfo.Pkg)
	packages := prog.AllPackages() // Build SSA code for bodies of functions in all packages
	for p := range packages {
		packages[p].Build()
	}
	rv := interp.Interpret(mainPkg, 0, "", nil)
	if rv != 0 {
		fmt.Printf("Interpreter error: %d\n", rv) // show any error
	}
}