doc: Improve <service-type> documentation.

* doc/guix.texi (Service Reference): Correct and clarify some statements
  regarding the "compose" and "extend" procedures of <service-type>.
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Chris Marusich 2018-03-29 07:29:49 +02:00
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@ -21090,16 +21090,16 @@ services.
Otherwise, it must be a one-argument procedure. The procedure is called Otherwise, it must be a one-argument procedure. The procedure is called
by @code{fold-services} and is passed a list of values collected from by @code{fold-services} and is passed a list of values collected from
extensions. It must return a value that is a valid parameter value for extensions. It may return any single value.
the service instance.
@item @code{extend} (default: @code{#f}) @item @code{extend} (default: @code{#f})
If this is @code{#f}, services of this type cannot be extended. If this is @code{#f}, services of this type cannot be extended.
Otherwise, it must be a two-argument procedure: @code{fold-services} Otherwise, it must be a two-argument procedure: @code{fold-services}
calls it, passing it the initial value of the service as the first argument calls it, passing it the initial value of the service as the first
and the result of applying @code{compose} to the extension values as the argument and the result of applying @code{compose} to the extension
second argument. values as the second argument. It must return a value that is a valid
parameter value for the service instance.
@end table @end table
@xref{Service Types and Services}, for examples. @xref{Service Types and Services}, for examples.