There are several errrors in this demo, fixed first one
Merge branch 'master' of https://github.com/cwi-swat/rascal.git
Now producing proper concrete lists as result of matching

Consider:

syntax D = "d";
syntax Ds = {D ","}*;

and the match
Removed ConcreteMatching[12].rsc (moved to rascal-test)
Remaining fixes
Merge branch 'master' of https://github.com/cwi-swat/rascal.git