goruby/goruby

package evaluator

import (
    "bytes"
    "fmt"
    "go/token"
)

type runtime interface {
    addFile(*token.File)
    pushToStack(name string, position int)
    popFromStack()
    String() string
}

func newRuntime() runtime {
    return &_runtime{}
}

type _runtime struct {
    currentFile    *token.File
    currentContext *executionContext
    stack          []*executionContext
}

func (r *_runtime) addFile(file *token.File) {
    r.currentFile = file
    if len(r.stack) == 0 {
        ctx := &executionContext{file: file}
        ctx.addStackFrame("<main>", 1)
        r.currentContext = ctx
        r.stack = append(r.stack, ctx)
    }
}

func (r *_runtime) pushToStack(name string, position int) {
    ctx := &executionContext{file: r.currentFile}
    ctx.addStackFrame(name, position)
    r.currentContext = ctx
    r.stack = append(r.stack, ctx)
}

func (r *_runtime) popFromStack() {
    r.stack = r.stack[:len(r.stack)-1]
    r.currentContext = r.stack[len(r.stack)-1]
}

func (r *_runtime) String() string {
    var out bytes.Buffer
    for _, ctx := range r.stack {
        fmt.Fprintln(&out, ctx.String())
    }
    return out.String()
}

type executionContext struct {
    file  *token.File
    frame frame
}

func (ec *executionContext) addStackFrame(name string, position int) error {
    epos := ec.file.Position(token.Pos(position))
    if epos.Filename == "" || !epos.IsValid() {
        return fmt.Errorf("Error finding context within file %q", ec.file.Name())
    }
    ec.frame = frame{context: name, position: epos}
    return nil
}

func (ec *executionContext) String() string {
    var out bytes.Buffer
    fmt.Fprintln(&out, ec.frame.String())
    return out.String()
}

type frame struct {
    context  string
    position token.Position
}

func (ef frame) String() string {
    return fmt.Sprintf("%s:in `%s'", ef.position, ef.context)
}