##### 37.6.4.3 Using loop structures

DITA2Go supports “while” loops, “repeat” loops, and “until” loops:

    <$_while (expr)>...<$_endwhile>    loops while expr is not 0 (zero)
    <$_repeat (expr)>...<$_endrepeat>  loops for the count of expr
    <$_until (expr)>...<$_enduntil>    loops while expr is false

“While” loops

For <$_while>, a runaway-prevention feature ends the loop after the maximum count specified in the following setting:

    [Macros]
    ; WhileMax = maximum count for <$_while>, to prevent runaways; the
    ;  current count can be accessed using predefined macro variable
    ;  <$$_wcount>
    WhileMax=128

Predefined variable <$$_wcount> contains the loop count, starting with 1 (one).

“Until” loops

Because “until” is really the same as “while not”, the <$_while> runaway-prevention limit also applies to <$_until> loops:

    [HtmlOptions]
    WhileMax=128

For example, a loop controlled by <$_until (0)> goes to the WhileMax limit, unless you include an effective <$_break>. Predefined variable <$$_wcount> contains the loop count, starting with 1 (one).

“Repeat” loops

For <$_repeat>, the runaway-prevention limit comes into play only if the count is set to zero:

    [Macros]
    ; RepeatMax = maximum count for <$_repeat> when value is not given, so
    ;  that loop continues until a <$_break condition> is met
    RepeatMax=128

The current loop count is held in predefined variable <$$_count>, and the down-count starting with expr is in predefined variable <$$_dcount>.

Nest loops

You cannot nest a <$_while> in a <$_while>, or a <$_repeat> in a <$_repeat>, in the same macro. Nor can you nest a <$_while> in an <$_until>, or an <$_until> in a <$_while>. Instead you can call another macro to run a sub-loop. However, you can nest a <$_while> in a <$_repeat>, or a <$_repeat> in a <$_while>, and you can use one layer of <$_if> in the mix:

    <$_while (expr)>
       <$_if (expr)>
          <$_repeat (expr)>...<$_endrepeat>
       <$_else>
          <$_repeat (expr)>...<$_endrepeat>
       <$_endif>
    <$_endwhile>

Move around within loops

You can use <$_break> to skip to the end of the loop, and <$_continue> to jump back to the start of the next iteration. Although you can invoke these control elements in <$_if>s, it is simpler to use the following constructs:

    <$_break if (expr)>
    <$_continue if (expr)>

Use only a single space before each if, and a minimum of one space after each if. These constructs work even in nested <$_while> or <$_repeat> loops, where they apply to the innermost of the loops where they occur.

Previous Topic: 37.6.4.2 Using conditional expressions

Next Topic: 37.6.5 Specifying substrings in expressions

Parent Topic: 37.6.4 Using control structures in expressions

Sibling Topics:

37.6.4.1 Understanding control-structure elements

37.6.4.2 Using conditional expressions

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