# Tracing Functions: Problem printing parameter values

**URL:** https://discourse.julialang.org/t/tracing-functions-problem-printing-parameter-values/80003
**Category:** General Usage
**Tags:** macros
**Created:** [April 25, 2022, 5:58pm UTC](https://discourse.julialang.org/t/tracing-functions-problem-printing-parameter-values/80003 "2022-04-25T17:58:19Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![Mark\_Nahabedian](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mark_nahabedian/32/16562_2.png) [@Mark\_Nahabedian](https://discourse.julialang.org/u/Mark_Nahabedian)
#### Post date: [April 25, 2022, 5:58pm UTC](https://discourse.julialang.org/t/tracing-functions-problem-printing-parameter-values/80003/1 "2022-04-25T17:58:19Z")

</div>

I’m trying to implement a function tracing facility in Julia. Each time the designated function is called I want to log the parameters and return values.

I have something partially working that is checked in at

> **[GitHub - MarkNahabedian/NahaJuliaLib.jl: Some utility functions for Julia...](https://github.com/MarkNahabedian/NahaJuliaLib.jl)**
>
> Some utility functions for Julia programming. Contribute to MarkNahabedian/NahaJuliaLib.jl development by creating an account on GitHub.

`@trace` is defined at

> <https://github.com/MarkNahabedian/NahaJuliaLib.jl/blob/7b3e88a54543a5a96207767849a2dbe3b34c0c4c/src/trace.jl#L68>

It has two problems:

- it prints the parameter names rather than their values
- I’m using `println` because when I use Logging.@info I get the error “ERROR: LoadError: LoadError: MethodError: no method matching logmsg\_code(::Module, ::String, ::Int64, ::Symbol)”.

```julia
using Pkg
Pkg.add(url="https://github.com/MarkNahabedian/NahaJuliaLib.jl")
using NahaJuliaLib
using MacroTools
@trace(trace_hanoi, function hanoi(from, to, other, count)
    if count == 1
        println("move 1 from $from to $to")
        return
    else
        hanoi(from, other, to, count - 1)
        println("move 1 from $from to $to")
        hanoi(other, to, from, count - 1)
        return (from, to) # arbitrary result to show
    end
end)
hanoi (generic function with 1 method)
trace_hanoi = true
true
hanoi(:a, :b, :c, 2)
Trace Enter hanoi(from, to, other, count)
Trace Enter hanoi(from, to, other, count)
move 1 from a to c
Trace Exit nothing
move 1 from a to b
Trace Enter hanoi(from, to, other, count)
move 1 from c to b
Trace Exit nothing
Trace Exit (:a, :b)

```

Note the “Trace Enter” lines. I’d like the first one to say

```julia
Trace Enter hanoi(:a, :b, :c, 2)

```

instead but can’t get the code right.

I don’t see how I can “unquote” the expressions further than they’ve been quoted. Can someone sugguest how I can get the values rather than the names of the parameters printed? The values are available at runtime, so that is when the expression needs to be constructed.

Note that I will also need to make this work for functions that take keyword arguments as well. That is why I’m constructing a :call Expr and then serializing it, rather than constructing a String directly.

Here’s the macroexpansion

```julia
striplines(@macroexpand(@trace(trace_hanoi, function hanoi(from, to, other, count)
    if count == 1
        println("move 1 from $from to $to")
        return
    else
        hanoi(from, other, to, count - 1)
        println("move 1 from $from to $to")
        hanoi(other, to, from, count - 1)
        return (from, to) # arbitrary result to show
    end
end)))
:($(Expr(:function, :(hanoi(from, to, other, count)), quote
    function var"##bodyfunction#274"()
        if count == 1
            println("move 1 from $(from) to $(to)")
            return
        else
            hanoi(from, other, to, count - 1)
            println("move 1 from $(from) to $(to)")
            hanoi(other, to, from, count - 1)
            return (from, to)
        end
    end
    if trace_hanoi
        (println)("Trace Enter ", (string)($(Expr(:copyast, :($(QuoteNode(:(hanoi(from, to, other, count)))))))))
    end
    var"##result#273" = var"##bodyfunction#274"()
    if trace_hanoi
        (println)("Trace Exit ", var"##result#273")
    end
end, Symbol("##result#273"))))

```

My problem is readily observable in the "Trace Enter " line. I don’t see how to get the values of the parameters rather than their names, given that their names are the result of calling `map` at macroexpansion time.

Thanks.