LOUT - how to do variable length arrows with labels?

[Paul A Blampied]

Hi, can anybody help me with this:

Without having to use the diagram package, I want to produce diagrams
involving horizontally composed arrows, possibly with labels above them,
e.g.:


      label1      longerlabel2
   A --------> B --------------> C --> D


from Lout code such as:

@CD @E {

  A
  @Arrow label {label1}
  B
  @Arrow label {longerlabel2}
  C
  @Arrow
  D

}

My problem is how to make the arrows the correct length.  This is how far
I have got with the definition:

extend  @Eq
def     @Arrow
  named label   {}      # Label to go along top of arrow
{
  @OneRow {
    @OneCol { ||0.5f label ||0.5f }     # Put some space either side of label
  ^/
    @OneCol {-->}
  }
}

Is it possible to extend the arrow to cover the full width of the label?
I have tried various combinations of @Wide and @Scale, but I can't seem
to get the right effect!

Paul Blampied
(address@hidden)