The Go Programming Language

12.3 Display, a Recursive Value Printer

Next we’ll take a look at how to improve the display of composite types. Rather than try to copy fmt.Sprint exactly, we’ll build a debugging utility function called Display that, given an arbitrarily complex value x, prints the complete structure of that value, labeling each element with the path by which it was found. Let’s start with an example.

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e, _ := eval.Parse("sqrt(A / pi)")
Display("e", e)

In the call above, the argument to Display is a syntax tree from the expression evaluator in Section 7.9. The output of Display is shown below:

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Display e (eval.call): e.fn = "sqrt" e.args[0].type = eval.binary e.args[0].value.op = 47 e.args[0].value.x.type ...