Info Catalog groff: Interpolating Registers groff: Registers groff: Assigning Register Formats

groff: Auto-increment

 
 5.8.3 Auto-increment
 --------------------
 
 Registers can also be incremented or decremented by a configured amount
 at the time they are interpolated.  The value of the increment is
 specified with a third argument to the 'nr' request, and a special
 interpolation syntax is used to alter and then retrieve the register's
 Auto-increment-Footnote-1::)
 
  -- Request: .nr ident value incr
      Set register IDENT to VALUE and its auto-incrementation amount to
      to INCR.  The '\R' escape sequence doesn't support an INCR
      argument.
 
    Auto-incrementation is not _completely_ automatic; the '\n' escape
 sequence in its basic form never alters the value of a register.  To
 apply auto-incrementation to a register, interpolate it with '\n±'.
 
  -- Escape sequence: \n+i
  -- Escape sequence: \n-i
  -- Escape sequence: \n+(id
  -- Escape sequence: \n-(id
  -- Escape sequence: \n+[ident]
  -- Escape sequence: \n-[ident]
      Increment or decrement IDENT (one-character name I, two-character
      name ID) by the register's auto-incrementation value and then
      interpolate the new register value.  If IDENT has no
      auto-incrementation value, interpolate as with '\n'.
 
      .nr a 0 1
      .nr xx 0 5
      .nr foo 0 -2
      \n+a, \n+a, \n+a, \n+a, \n+a
      .br
      \n-(xx, \n-(xx, \n-(xx, \n-(xx, \n-(xx
      .br
      \n+[foo], \n+[foo], \n+[foo], \n+[foo], \n+[foo]
          => 1, 2, 3, 4, 5
          => -5, -10, -15, -20, -25
          => -2, -4, -6, -8, -10
 
    To change the increment value without changing the value of a
 register, assign the register's value to itself by interpolating it, and
 specify the desired increment normally.  Apply an increment of '0' to
 disable auto-incrementation of the register.
 

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