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60 lines
1.1 KiB
Go
60 lines
1.1 KiB
Go
package main
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import (
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"fmt"
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"sort"
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)
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type UnknownSymbolError struct{ symbol }
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func (u UnknownSymbolError) Error() string {
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return fmt.Sprintf(`unknown symbol "%v"`, u.symbol)
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}
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type environment struct {
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items map[symbol]interface{}
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outer *environment
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}
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func newEnvironment(outer *environment) *environment {
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return &environment{
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items: make(map[symbol]interface{}),
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outer: outer,
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}
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}
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func (e environment) get(key symbol) (interface{}, error) {
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v, ok := e.items[key]
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if ok {
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debugPrint(fmt.Sprintf(`found key "%v": %v`, key, v))
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return v, nil
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}
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if e.outer != nil {
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return e.outer.get(key)
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}
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return nil, UnknownSymbolError{key}
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}
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func (e environment) set(key symbol, val interface{}) {
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e.items[key] = val
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}
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func (e environment) keys() []string {
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keys := make([]string, 0, len(e.items))
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for key, _ := range e.items {
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keys = append(keys, string(key))
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}
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if e.outer != nil {
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keys = append(keys, e.outer.keys()...)
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}
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sort.Strings(keys)
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return keys
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}
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func (e environment) defined(key symbol) bool {
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_, err := e.get(key)
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return err == nil
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}
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