good good study, day day up!

vendor/gopl.io/ch7/eval/print.go

@@ -0,0 +1,52 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+package eval
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// Format formats an expression as a string.
+// It does not attempt to remove unnecessary parens.
+func Format(e Expr) string {
+	var buf bytes.Buffer
+	write(&buf, e)
+	return buf.String()
+}
+
+func write(buf *bytes.Buffer, e Expr) {
+	switch e := e.(type) {
+	case literal:
+		fmt.Fprintf(buf, "%g", e)
+
+	case Var:
+		fmt.Fprintf(buf, "%s", e)
+
+	case unary:
+		fmt.Fprintf(buf, "(%c", e.op)
+		write(buf, e.x)
+		buf.WriteByte(')')
+
+	case binary:
+		buf.WriteByte('(')
+		write(buf, e.x)
+		fmt.Fprintf(buf, " %c ", e.op)
+		write(buf, e.y)
+		buf.WriteByte(')')
+
+	case call:
+		fmt.Fprintf(buf, "%s(", e.fn)
+		for i, arg := range e.args {
+			if i > 0 {
+				buf.WriteString(", ")
+			}
+			write(buf, arg)
+		}
+		buf.WriteByte(')')
+
+	default:
+		panic(fmt.Sprintf("unknown Expr: %T", e))
+	}
+}