— Request: .while expr anything

Evaluate the expression expr, and repeatedly execute anything (the remainder of the line) until expr evaluates to 0.

          
          .nr a 0 1
          .while (\na < 9) \{\
          \n+a,
          .\}
          \n+a
              ⇒ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

Some remarks.

• The body of a while request is treated like the body of a de request: gtroff temporarily stores it in a macro which is deleted after the loop has been exited. It can considerably slow down a macro if the body of the while request (within the macro) is large. Each time the macro is executed, the while body is parsed and stored again as a temporary macro.

                 
                 .de xxx
                 .  nr num 10
                 .  while (\\n[num] > 0) \{\
                 .    \" many lines of code
                 .    nr num -1
                 .  \}
                 ..
  

  The traditional and ofter better solution (UNIX troff doesn't have the while request) is to use a recursive macro instead which is parsed only once during its definition.

                 
                 .de yyy
                 .  if (\\n[num] > 0) \{\
                 .    \" many lines of code
                 .    nr num -1
                 .    yyy
                 .  \}
                 ..
                 .
                 .de xxx
                 .  nr num 10
                 .  yyy
                 ..
  

  Note that the number of available recursion levels is set to 1000 (this is a compile-time constant value of gtroff).

• The closing brace of a while body must end a line.

                 
                 .if 1 \{\
                 .  nr a 0 1
                 .  while (\n[a] < 10) \{\
                 .    nop \n+[a]
                 .\}\}
                     ⇒ unbalanced \{ \}
  

— Request: .break

Break out of a while loop. Be sure not to confuse this with the br request (causing a line break).

— Request: .continue

Finish the current iteration of a while loop, immediately restarting the next iteration.