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Re: [Groff] blm blues

From: Werner LEMBERG
Subject: Re: [Groff] blm blues
Date: Tue, 11 Nov 2008 08:15:40 +0100 (CET)

> I am trying to produce a macro for request blm that would set space
> as a given fraction of the current vertical spacing.
> I did the following:
> .de blank
> .  nr blankreg (c;\\$1)
> ..
> .de blank_aux
> .  sp (\\n[.v]u*\\n[blankreg]u/28340)u
> ..
> .blm blank_aux
> This does not work (does not produce any space).

Again, you haven't applied `u' correctly.  In a request which doesn't
use `u' as the default scaling indicator, *each* element gets
converted to the request's default unit before it is processed
arithmetically.  In your example, the `28340' is converted to `v'
also.  Additionally, it has no effect to apply `u' to an expression.
The right way to write the call to .sp is

  .sp (\\n[.v]u * \\n[blankreg]u / 28340u)

Alternatively, you might write

  .sp (u;(\\n[.v] * \\n[blankreg] / 28340))

See section 5.2.1 (Default Units) in for more examples.


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