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environment.go
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/
environment.go
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package deslang
import (
"errors"
)
// lookup table for declared variables
type Environment struct {
values map[string]BasicLit
Enclosing *Environment // parent scope
global bool // global scope
}
func NewEnvironment(global bool) *Environment {
return &Environment{
values: make(map[string]BasicLit),
global: global,
}
}
func (env *Environment) Assign(tok Token, val BasicLit) error {
s := string(tok.Lexeme)
if _, has := env.values[s]; has {
env.values[s] = val
return nil
}
// As long as it hasn't reached the global scope, recursively check the chain
// of environments.
if !env.global {
err := env.Enclosing.Assign(tok, val)
if err != nil {
return err
}
}
return errors.New("Undefined variable '" + s + "'.")
}
func (env *Environment) Define(name string, lit BasicLit) {
env.values[name] = lit
}
func (env *Environment) Get(tok Token) (BasicLit, error) {
var lit BasicLit
// Recursively look for the variable.
lit, has := env.values[string(tok.Lexeme)]
if !has {
if env.global {
return lit, errors.New("Undefined variable '" + string(tok.Lexeme) + "'.")
}
return env.Enclosing.Get(tok)
}
return lit, nil
}