Using string interpolation in an overlay results in the following kind of error:

    [java] [ Main | critical ] Cannot generate congruence definition from overlay definition
    [java]            ["EXTERNAL_DEF_RULE","(","3",")"]
    [java] Cannot generate congruence definition from overlay definition
    [java] 	"EXTERNAL_DEF_RULE(3)"

which is a bad error message, but there does not seem to be a reason why string interpolation cannot be used in an overlay?

Submitted by Gabriël Konat on 7 May 2014 at 17:42

Not a great error message indeed. The reason for the rejection is that string interpolation is compiled down to a series of applications of concat-strings, but strategy applications are not allowed in an overlay declaration. Perhaps the improvement should be in the way overlays are compiled.

Overlays allow for both matching and building. Building with string interpolation is fine, but matching is much trickier. Should greedy matching be used? How does $[ function x [y] ] match “function q() { r(); }”? I’d just tweak the error message for this one and use regular expressions when string matching is needed. (And I’m also not really a fan of overlays in the first place.) Just my .02.