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feat(builtin): add dump() for easy print-based debugging #1269

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feat(builtin): add dump() for easy print-based debugging #1269

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feat(builtin): add `dump()` for easy print-based debugging
rami3l Nov 29, 2024
7b2f8d3
Merge branch 'main' into feat/dump
rami3l Dec 2, 2024
7204d46
Merge branch 'main' into feat/dump
bobzhang Dec 3, 2024
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2 changes: 2 additions & 0 deletions builtin/builtin.mbti
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@ fn assert_not_eq[T : Eq + Show](T, T, loc~ : SourceLoc = _) -> Unit!

fn assert_true(Bool, loc~ : SourceLoc = _) -> Unit!

fn dump[T](T, name? : String, loc~ : SourceLoc = _) -> T //deprecated

fn fail[T](String, loc~ : SourceLoc = _) -> T!Failure

fn ignore[T](T) -> Unit
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15 changes: 15 additions & 0 deletions builtin/console.mbt
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Expand Up @@ -15,6 +15,9 @@
///|
fn println_mono(s : String) -> Unit = "%println"

///|
fn any_to_string[T](any : T) -> String = "%any.to_string"

///|
pub fn println[T : Show](input : T) -> Unit {
println_mono(input.to_string())
Expand All @@ -26,6 +29,18 @@ pub fn print[T : Show](input : T) -> Unit {
println(input)
}

///|
/// Prints and returns the value of a given expression for quick and dirty debugging.
/// @alert deprecated "This function is for debugging only and should not be used in production"
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@rami3l rami3l Nov 29, 2024 •
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This function is marked as deprecated because it seems to be the only way to generate warnings with it. In Rust this logic is handled by clippy instead of rustc so there haven't been such concerns.

pub fn dump[T](t : T, name? : String, loc~ : SourceLoc = _) -> T {
let name = match name {
Some(name) => name
None => ""
}
println("dump(\{name}@\{loc}) = \{any_to_string(t)}")
t
}

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any_to_string is introduced for arbitrary code transformations where T is not sure if it satsifies Show. How is this different from dump[T:Show](...)
cc @Guest0x0 it makes sense to introduce support of ArgsRepr which is essentialy a stringified repr of args. so that we can do something like this:

pub fn dump[T:Show](t : T, name~ : ArgsRepr = _, loc~ : SourceLoc = _) -> T

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@rami3l rami3l Dec 4, 2024 •
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@bobzhang One thing that distinguishes Swift's dump() from Rust's dbg!() is that the former doesn't pose any restrictions on T whereas the latter depends on T: Debug (which is exclusively used for print-oriented pretty-printing, compensating for the lack of a built-in dumper in Rust) 1.

I think the Show trait in MoonBit corresponds to the Display trait (which subsumes .to_string() in Rust) rather than Debug, so it makes more sense to add no bounds at all.

OTOH ArgsRepr will definitely be a nice addition.

Footnotes

  1. The lack of distinction between Display and Debug seems like a common reason for which print-based debugging is less popular in traditional tech stacks; both approaches here allow the mitigation of this issue. ↩

///|
pub fn to_string(self : Bool) -> String {
if self {
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