Missing {res} when -display- is*used in a loop

[Nils Enevoldsen]

Stata erroneously omits {res} when -display- is used in a loop, causing the displayed result to take the display style of the previous line. If there is no other previous style, it takes the {com} style of the loop itself.

When -display- is used in -foreach-, -forvalues-, or -while-, it should print:

{res} foo

But instead it prints:

foo

This is not a new issue, and as of five years ago technical support even reported that they were "taking a look". I've re-reported the issue, but am also posting here for searchability. In addition, I clarify that the issue is not simply that "as error" persists. Other styles also persist, such as "as text", "as input", and even the "command" style of the loop itself.

// Demonstrate issue with -forvalues-:
forvalues i = 1/1 {
    display "implicit res <- bug"
    display as err "explicit err <- properly styled"
    display "implicit res <- bug"
    display as txt "explicit txt <- properly styled"
    display "implicit res <- bug"
    display as com "explicit com <- properly styled"
    display "implicit res <- bug"
    display as res "explicit res <- properly styled"
    display "implicit res <- technically bug, but properly styled anyway"
}

. // Demonstrate issue with -forvalues-:
. forvalues i = 1/1 {c -(}
{txt}  2{com}.     display "implicit res <- bug"
{txt}  3{com}.     display as err "explicit err <- properly styled"
{txt}  4{com}.     display "implicit res <- bug"
{txt}  5{com}.     display as txt "explicit txt <- properly styled"
{txt}  6{com}.     display "implicit res <- bug"
{txt}  7{com}.     display as com "explicit com <- properly styled"
{txt}  8{com}.     display "implicit res <- bug"
{txt}  9{com}.     display as res "explicit res <- properly styled"
{txt} 10{com}.     display "implicit res <- technically bug, but properly styled anyway"
{txt} 11{com}. {c )-}
implicit res <- bug
{err}explicit err <- properly styled
implicit res <- bug
{txt}explicit txt <- properly styled
implicit res <- bug
{com}explicit com <- properly styled
implicit res <- bug
{res}explicit res <- properly styled
implicit res <- technically bug, but properly styled anyway

[Nils Enevoldsen]

Stata Technical Support has responded to me, saying that this behavior is intended, because,

Sometimes you want to put SMCL into a certain mode/color and have the subsequent -display- commands come out in whatever mode you set. Therefore -display- itself can't reset the SMCL mode.

This happens in loops as well, because loops are "implicit programs":

Inside a program or an implicit program (i.e. a loop, which needs to create a hidden program to store the lines inside the loop to be executed over and over), the SMCL mode is not set or reset at any point.

However a running do-file/ado-file is not an implicit program, so the behavior is different there. This doesn't seem optimal to me, but I will learn to live with it.

Even Stata's own documentation, such as the examples in -help foreach-, ends up printing text in {com} mode.

foreach name in "Annette Fett" "Ashley Poole" "Marsha Martinez" {
        display length("`name'") " characters long -- `name'"
}

Long story short: I should get in the habit of always specifying the mode when using -display-.