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62 lines
1.5 KiB
Go
62 lines
1.5 KiB
Go
package main
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import (
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"fmt"
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"reflect"
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)
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type special func(*environment, ...interface{}) (interface{}, error)
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func define(env *environment, args ...interface{}) (interface{}, error) {
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if len(args) != 2 {
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return nil, fmt.Errorf(`received %d arguments in *define*, expected exactly 2`, len(args))
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}
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s, ok := args[0].(symbol)
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if !ok {
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return nil, fmt.Errorf(`first argument to *define* must be symbol, received %v`, reflect.TypeOf(args[0]))
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}
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v, err := eval(args[1], env)
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if err != nil {
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return nil, err
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}
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env.set(s, v)
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return nil, nil
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}
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func quote(_ *environment, args ...interface{}) (interface{}, error) {
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return sexp(args), nil
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}
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func _if(env *environment, args ...interface{}) (interface{}, error) {
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if len(args) != 3 {
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return nil, fmt.Errorf(`received %d arguments in *if*, expected exactly 3`, len(args))
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}
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v, err := eval(args[0], env)
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if err != nil {
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return nil, err
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}
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if b, ok := v.(bool); ok && !b {
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return eval(args[2], env)
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}
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return eval(args[1], env)
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}
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func set(env *environment, args ...interface{}) (interface{}, error) {
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if len(args) != 2 {
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return nil, fmt.Errorf(`received %d arguments in *set!*, expected exactly 2`, len(args))
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}
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s, ok := args[0].(symbol)
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if !ok {
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return nil, fmt.Errorf(`first argument to *set!* must be symbol, received %v`, reflect.TypeOf(args[0]))
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}
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if !env.defined(s) {
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return nil, fmt.Errorf(`cannot *set!* undefined symbol %v`, s)
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}
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v, err := eval(args[1], env)
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if err != nil {
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return nil, err
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}
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env.set(s, v)
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return nil, nil
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}
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