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40 lines
684 B
Go
40 lines
684 B
Go
package main
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import (
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"fmt"
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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 (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) 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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