Info Catalog groff: if-else groff: Conditionals and Loops

groff: while

 
 5.20.3 while
 ------------
 
 'gtroff' provides a looping construct using the 'while' request, which
 is used much like the 'if' (and related) requests.
 
  -- 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 that
           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 that 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.
 
    Expressions.
 

Info Catalog groff: if-else groff: Conditionals and Loops