ER: debug/1

[pkoppstein]

There have been several proposals for adding debug/1 for convenience.

In particular, @nicowilliams mentioned:

def debug($msg): ("\($msg): \(.)|debug|empty), .;

This has good memory-management characteristics, but includes "(.)" unconditionally, which reduces flexibility and can lead to very long debug messages that can potentially cause problems. Thus I would like to propose a similar but simpler definition:

def debug(msg): (msg | debug | empty), .;

This would allow tailored messages such as: debug("entering foo(\(arg1); \(arg2))")

while still allowing . to be prepended with a string, at a cost of just a few extra keystrokes:

debug("hello: \(.)")

Or one could go with:

debug("hello", .)

---

Footnote:

#2112 proposes:

def debug(f): . as $val | f | debug | $val;

but this def effectively presupposes that f is a singleton, for if
one were to use it and wrote debug("msg1"; "msg2"), an undesirable fork would result.

The two defs above avoid this issue, and indeed make it easy to split up a debug message over more than one line, while keeping them together.

[itchyny]

Ref: #2111, #2112