What are expl3 equivalents for various macros useful to debugging and a building private packages

Question

When I'm writing my own private style packages, such as when developing them, I find it useful to use typeout to help me see what I've currently created or figure out what line of code is the source of the issues (particularly when a mysterious error message is getting thrown).

Currently, I'm refractoring some old expl3 code I created back when I  understood very little expl3.  Throughout that code I've got things like typeout and a judicious sprinkling of space thrown in there to make terminal output simple and easy to read.  I've come to actually like this terminal output because it helps me debug things, but I can't find anything expl3 equivalents of typeout.  The best I can find is msg_warning:... which throws too much to the terminal.

Similarly, I like that I can concatenate space to create larger white space on the terminal screen.  Concatenating ~ doesn't work.

A third macro I've come to really appreciate when debugging and outputting to terminal is detokenize.

It would seem that when write expl3, I should stick with expl3 macros and such.  Does anyone have any suggestions about writing expl3 equivalents for:

typeout{....}
detokenize{....}
space

egreg · Accepted Answer

You want iow_term:n that expands macros in the usual way.

RequirePackage{expl3}

ExplSyntaxOn

iow_term:n {Hi,~Andrew,~how~are~you?~This~message~will~automatically~
 wrap~when~reaching~a~predefinedc_space_tl limit. \ \
 You~can~force~a~break~and~use~exp_not:N tl_to_str:n
 for~showing~tl_to_str:n{whatever~you~want}}

This will output

*************************************************
* Hi, Andrew, how are you? This message will automatically wrap when
* reaching a predefined limit.
* 
* You can force a break and use tl_to_str:n for showing whatever you want 
*************************************************

So iow_term:n is the analog of typeout, while tl_to_str:n is detokenize; a space is c_space_tl, which is exactly the same as space.

There's also iow_log:n for writing to the log file only.

Jérôme LAURENS · Answer

The first answer is no longer accurate, no more stars and the expansion policy has changed. One must adapt to use either iow_term:n or iow_term:x, the former expands nothing while the latter expands... what is expandable.
Here is an example with various settings to illustrate how to expand some macros, or not.
documentclass{minimal}
ExplSyntaxOn
tl_set:Nn l_tmpa_tl { 2 + 2 }
int_set:Nn l_tmpa_int { l_tmpa_tl }
iow_term:n{****~iow_term:n :~l_tmpa_tl~=~l_tmpa_int}
iow_term:x{****~iow_term:x :~l_tmpa_tl~c_space_tl=~l_tmpa_int}
iow_term:x{****~iow_term:x :~l_tmpa_tl~c_space_tl=~int_use:Nl_tmpa_int}
iow_term:x{****~iow_term:x :~exp_not:N l_tmpa_tl~=~int_use:Nl_tmpa_int}
ExplSyntaxOff
begin{document}
end{document}

The terminal output reads
**** iow_term:n : l_tmpa_tl = l_tmpa_int 
**** iow_term:x : 2+2 = l_tmpa_int 
**** iow_term:x : 2+2 = 4
**** iow_term:x : l_tmpa_tl = 4

The c_space_tl was sometimes necessary to insert a space before the =.

David Carlisle · Answer

grep is your friend:

l3kernel/l3tl.dtx:cs_new_eq:NN tl_to_str:n etex_detokenize:D

l3kernel/l3tl.dtx:tl_const:Nn c_space_tl { ~ }

for messages if you don't like the msg functions, probably typeout is still your friend.

What are expl3 equivalents for various macros useful to debugging and a building private packages

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