'mm' scaling value on top-level

[Werner LEMBERG]

Folks,


This is a comment of mine from !929:

======================================================================

The change to enable pairs [in `#(set-default-paper-size)`] is almost
trivial:

```
--- a/scm/paper.scm
+++ b/scm/paper.scm
@@ -314,7 +314,9 @@ unless explicitly overridden in the name."
      scaled-values)))
 
 (define (internal-set-paper-size module name landscape?)
-  (let* ((entry (lookup-paper-name module name landscape?))
+  (let* ((entry (if (pair? name)
+                    name
+                    (lookup-paper-name module name landscape?)))
          (is-paper? (module-defined? module 'is-paper)))
     (cond
      ((not is-paper?)
```

Using it with

```
#(set-default-paper-size (cons 100 50)))
```

works like a charm.  However, code like

```
#(set-default-paper-size (cons (* 100 mm) (* 50 mm)))
```

doesn't work; I get the error message

```
error: GUILE signaled an error for the expression beginning here
#
 (set-default-paper-size (cons (* 100 mm) (* 50 mm)))
Unbound variable: mm
```

What must I do to make 'mm' and similar dimension scale values
available at the top level?

======================================================================

I guess not everyone is reading the MR tracker stuff, so I ask here
directly.  Any help is greatly appreciated.


    Werner