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https://github.com/gopl-zh/gopl-zh.github.com.git
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59 lines
1.1 KiB
Go
59 lines
1.1 KiB
Go
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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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package eval
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import (
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"fmt"
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"strings"
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)
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//!+Check
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func (v Var) Check(vars map[Var]bool) error {
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vars[v] = true
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return nil
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}
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func (literal) Check(vars map[Var]bool) error {
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return nil
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}
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func (u unary) Check(vars map[Var]bool) error {
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if !strings.ContainsRune("+-", u.op) {
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return fmt.Errorf("unexpected unary op %q", u.op)
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}
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return u.x.Check(vars)
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}
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func (b binary) Check(vars map[Var]bool) error {
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if !strings.ContainsRune("+-*/", b.op) {
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return fmt.Errorf("unexpected binary op %q", b.op)
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}
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if err := b.x.Check(vars); err != nil {
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return err
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}
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return b.y.Check(vars)
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}
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func (c call) Check(vars map[Var]bool) error {
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arity, ok := numParams[c.fn]
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if !ok {
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return fmt.Errorf("unknown function %q", c.fn)
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}
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if len(c.args) != arity {
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return fmt.Errorf("call to %s has %d args, want %d",
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c.fn, len(c.args), arity)
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}
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for _, arg := range c.args {
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if err := arg.Check(vars); err != nil {
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return err
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}
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}
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return nil
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}
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var numParams = map[string]int{"pow": 2, "sin": 1, "sqrt": 1}
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//!-Check
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