Now with maps and structs!

[burakemir]

And our first announcement: Mangle has maps and structs. These are useful for representing structured data, similar to JSON or protocol buffers.

Proper documentation is in the works, but in short, there are built-in functions fn:map and fn:struct which construct maps and struct constants. Until then, you may want to check out some unit tests.

A map expression is simply an apply expression fn:map( key_1, val_1, ..., key_n, val_n) with a convenient syntax [ key_1 : val_1, ..., key_n : val_n ]. A type expression for map types is fn:Map(Key, Val) and it conforms to .fn:Map(Key2, Val2) if Key2 conforms to Key1 and Val1 conforms to Val2.

Structs are written fn:struct( key_1, val_1, ..., key_n, val_n) with a convenient syntax { key_1 : val_1, ..., key_n : val_n } A type expression for struct types is fn:Struct(key_1, Val_1, ..., key_n, Val_n) where each key_i is a name constant, and it conforms to another struct type if it is "longer" and has conforming values for matching keys.

In both cases, the convenient syntax is shorthand for the apply expression (it still involves a function symbol). Any rule that involves apply expressions could construct an unbounded number of tuples (unlike a proper datalog rule), and one has to be careful about non-termination.

Accessing data from maps and structs happens with the new built-in match predicates :match_entry(Map, Entry, Value) (for maps) and :match_field(Struct, Key, Value) or by checking equality.