What about integers being keys. That works fine. How does a 3 level deep map work with clauses The most straightforward manner is like you would do this in a

What about integers being keys. That works fine. How does a 3 level deep map work with clauses The most straightforward manner is like you would do this in a relational database (if the goal is to keep O(1) times). E.g. two-level: foo(a,x). foo(b,y). bar(x,a-x-one). bar(x,a-x-two). bar(y,b-y-one). Again, you can add predicates to make this less unwieldy. If the JSON conforms to a schema, there is also the possibility of mapping particular keys to arguments. Since you know the set of possible keys in such a case, you could map keys to fixed term arguments. E.g. a structure such as: { "foo": "apple", "bar": "pear" } Could be mapped to: json(apple,pear) You would have the same You could do this for deeper maps as well. It gives you the same benefits as hash maps, O(1) indexing. In fact, the Hdrug[1] system uses such a representation for partially typed feature structures, which can have an arbitrary depth. It provides a DSL for easily specifying types (the 'schema') and unifying structures and substructures. There is also a short description in the introductory chapters of my thesis, though it is definitely not my work ;). Note: I am not for or against adding maps to the language. There are probably applications where they are very handy in Prolog. For the things I worked on in Prolog I never really needed first-class maps. [1] http://www.let.rug.nl/~vannoord/Hdrug/ http://www.let.rug.nl/~vannoord/Hdrug/ [2] http://danieldk.eu/Research/Publications/phd-thesis.pdf http://danieldk.eu/Research/Publications/phd-thesis.pdf (starting at the end of page 19)