Using `format/2` with attributed variable on a pengine

[ridgeworks]

Got stuck so opened a new topic:

Use of `attribute_goals//1` to compose answers

Apologies on the length of this post but think I need to provide some motivation. Background: Attributed variables are a core feature supporting many (most?) CLP dialects on Prolog. By permitting logic variables to be “annotated”, they effectively permit constraint networks to be constructed without requiring a separately managed constraint store, really a brilliant idea IMHO. The constraint networks built using attributed variables are terms which are typically cyclic (they’re graphs) and can…