JSON Quickstart

This page shows the fastest way to parse and generate JSON in PyLog using the new built‑ins and dual representations.

Parse JSON text (classic)

?- atom_json_term('{"name":"test","value":42}', T, []).
T = json([name=test, value=42]).

?- atom_json_term('[1,2,true,null]', L, []).
L = [1, 2, @(true), @(null)].

Parse JSON text (dict mode)

?- atom_json_term('{"name":"alice","age":30}', D, [mode(dict)]).
D = {name:alice, age:30}.

% SWI‑compatible alias
?- atom_json_term('{"name":"alice","age":30}', D, [json_object(dict)]).
D = {name:alice, age:30}.

Generate JSON from terms

% Classic → JSON atom
?- T = json([inner=json([value=42])]), atom_json_term(A, T, []).
A = '{"inner": {"value": 42}}'.

% Dict → JSON atom (dict mode)
?- D = {ok:true}, atom_json_term(A, D, [mode(dict)]).
A = '{"ok": true}'.

Round‑trips

% Classic
?- atom_json_term(A, json([k=v]), []).
A = '{"k": "v"}'.

% Dict
?- atom_json_term('{"k":true}', D, [mode(dict)]), atom_json_term(A, D, [mode(dict)]).
D = {k:true},
A = '{"k": true}'.

Constants and representations

• Classic uses @(null), @(true), @(false).
• Dict uses atoms null, true, false.
• Objects are unordered; PyLog uses canonical key sorting.

Notes

• Prefer atom_json_term/3 for pure Prolog workflows.
• For file/stream I/O (embedding PyLog in Python), use json_read/3, json_write/3, json_read_dict/3, json_write_dict/3 with file‑like streams. See Reference → JSON for details.

See also

• Reference → JSON: mapping, options (mode/1, json_object/1), error handling
• Basics → Dicts: dict_create/3, get_dict/3, put_dict/3