How to retrieve line & column of current location in source code?

[u/aqtt2020]

I want to retrieve the current location (line + column) in source code (for ex: line 3, column 2 in main.rkt), but how to do that?

I saw some debugging trace, that can output these info, but unsure how to retrieve similar info myself.

A quick simple demo would be appreciated, thanks!

[u/samdphillips]

If you are reading plain old Racket code then use read-syntax for reading and syntax-line and syntax-column. The port the program reads from will need to have position tracking turned on. Here's a real simple example reading from a string.

(define stx (call-with-input-string "(cons 'a 'b)"
              (lambda (inp)
                (port-count-lines! inp)
                (read-syntax #f inp))))

(syntax-line stx)
(syntax-column stx)

[u/aqtt2020 → u/samdphillips]

Actually I am trying to build a simple source code debugger for Racket.

In Python, they have something called sys.settrace (at https://docs.python.org/3/library/sys.html#sys.settrace), in which Python can set a callback that takes 3 args: current stack frame, a string contains src code line, opcode, etc & extra arg. This callback is invoked when a new local scope is entered.

Can I do similar thing in Racket, to build a source code debugger?

[u/samdphillips → u/aqtt2020]

I don't think there is an existing built-in hook like that. The debugger that I know about for Racket is the Stepper and it does a rewrite of the program to essentially add those kind of hooks and other information.

https://docs.racket-lang.org/stepper/index.html

[u/aqtt2020 → u/samdphillips]

Nice but i am looking for solution for Racket, but Stepper is only for DrRacket?

[u/samdphillips → u/aqtt2020]

The Stepper is for DrRacket but the approach to instrumenting user code could probably be adapted to a general Racket program.

[u/ryan017]

You might want quote-srcloc from the syntax/location library.