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<a class="link" href="appendix-i-keywords.html">Appendix I: Keywords</a>
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<h1 class="main">Trace</h1>
<p>Another feature of <code>v.debug</code> is the possibility to add hook functions
before and after each function call.</p>
<p>To enable this feature, add the <code>-d trace</code> switch when building or running
your code:</p>
<div class="language-v">import v.debug
fn main() {
hook1 := debug.add_before_call(fn (fn_name string) {
println('> before ${fn_name}')
})
hook2 := debug.add_after_call(fn (fn_name string) {
println('> after ${fn_name}')
})
anon := fn () {
println('call')
}
anon()
// optionally you can remove the hooks:
debug.remove_before_call(hook1)
debug.remove_after_call(hook2)
anon()
}
</div>
<pre><code>$ v -d trace run example.v
> before anon
call
> after anon
call
</code></pre>
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