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https://github.com/gopl-zh/gopl-zh.github.com.git
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53 lines
940 B
Go
53 lines
940 B
Go
// 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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"bytes"
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"fmt"
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)
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// Format formats an expression as a string.
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// It does not attempt to remove unnecessary parens.
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func Format(e Expr) string {
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var buf bytes.Buffer
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write(&buf, e)
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return buf.String()
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}
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func write(buf *bytes.Buffer, e Expr) {
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switch e := e.(type) {
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case literal:
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fmt.Fprintf(buf, "%g", e)
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case Var:
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fmt.Fprintf(buf, "%s", e)
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case unary:
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fmt.Fprintf(buf, "(%c", e.op)
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write(buf, e.x)
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buf.WriteByte(')')
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case binary:
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buf.WriteByte('(')
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write(buf, e.x)
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fmt.Fprintf(buf, " %c ", e.op)
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write(buf, e.y)
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buf.WriteByte(')')
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case call:
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fmt.Fprintf(buf, "%s(", e.fn)
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for i, arg := range e.args {
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if i > 0 {
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buf.WriteString(", ")
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}
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write(buf, arg)
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}
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buf.WriteByte(')')
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default:
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panic(fmt.Sprintf("unknown Expr: %T", e))
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}
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}
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