ddlog happily string-izes function references to unhelpful closure description

[blp]

The following program:

function f(): string { "mystring" }
output relation X(x: string)
X("${f}").

yields this output:

X:
X{.x = "<closure: f, captured_args: ()>"}: +1

Of course, what I meant was:

function f(): string { "mystring" }
output relation X(x: string)
X("${f()}").

which outputs as expected:

X:
X{.x = "mystring"}: +1

I think that the compiler should be less willing to convert function references to strings this way.

[ryzhyk]

This was meant as a useful debugging feature, but I can see how it is confusing.

[mihaibudiu]

Could be a warning

[Kixiron]

I don't think this should be implicit behavior at all, if anything it should be an explicitly-called method on functions

[ryzhyk]

We can keep this behavior in debug printing (pring::debug() and ddlog_std::to_string_debug()).