juliensf / mercury-json Goto Github PK
View Code? Open in Web Editor NEWA Mercury JSON library.
License: BSD 2-Clause "Simplified" License
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mercury-json's Issues
Unused imports warning
Following is a warning message when compiling mercury-json with --warn-unused-imports enabled.
mercury-json/src/json.m:1023: In module `json':
mercury-json/src/json.m:1023: warning: module `univ' has a
mercury-json/src/json.m:1023: `:- import_module' declaration, but
mercury-json/src/json.m:1023: is not used anywhere in the module.
I'm using Mercury 22.01.5.
Failed to convert JSON objects to Mercury maps
When trying to convert JSON objects to Mercury maps, a confusing error will be reported, i.e.:
conversion to tree234.tree234(string, list.list(string)): argument is object, expected object
Following is demo code:
:- module test.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
:- import_module json.
:- import_module list.
:- import_module map.
:- import_module maybe.
:- import_module string.
main(!IO) :-
Result = json.from_json(
json.det_from_string(
"{\"foo\": [\"a\", \"b\"], \"bar\": [\"c\"]}")),
( Result = maybe.ok(Data : map(string, list(string))),
io.write_line(Data, !IO)
; Result = maybe.error(Error),
io.write_line(Error, !IO)
).
Tested Mercury version is:
Mercury Compiler, version rotd-2019-08-16, on x86_64-pc-linux-gnu
Performance issue when parsing large JSON data
It seems that mercury-json has a poor performance when parsing large JSON data.
For example, using following Python snippet to generate some random data:
import json
import random
with open("data.json", "w") as f: json.dump([[random.random() for i in range(5)] for i in range(5000)], f)Then trying to load data using mercury-json:
:- module main.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
:- import_module list.
:- import_module string.
:- import_module require.
:- import_module json.
main(!IO) :-
io.read_named_file_as_string("data.json", Result, !IO),
( Result = io.ok(Data),
( json.from_string(Data, json.array(Rows)) ->
io.write_string(string.format("rows = %d\n", [i(list.length(Rows))]), !IO)
; require.error("Invalid JSON")
)
; Result = io.error(Error),
require.error(io.error_message(Error))
).Convert Mercury maps to JSON objects
When trying to convert Mercury map to JSON object, a list of key and value pair objects is returned, instead of an object, which I think is not quite correct.
For example, with following demo code, the result is:
[{"key":"bar","value":["c"]},{"key":"foo","value":["a","b"]}]
Instead of:
{"bar": ["c"], "foo": ["a", "b"]}
Demo code:
:- module test.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
:- import_module json.
:- import_module list.
:- import_module map.
:- import_module pair.
main(!IO) :-
Json = json.to_json(
map.from_assoc_list(
["foo" - ["a", "b"], "bar" - ["c"]])),
json.write_compact(Json, !IO).
Tested on:
Mercury Compiler, version rotd-2019-08-16, on x86_64-pc-linux-gnu
Misleading error message
The following JSON, containing an unterminated string literal,
{ "compatible_crews": [ "37003 ] }
results in the following misleading error message from the parser:
bug.json:4:0: error: unescaped control character: U+000A
(It's technically correct but quite confusing.)
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