Rand Stats



Build Status


A naive imperative JSON parser in pure Raku (but with direct access to nqp:: ops), to evaluate performance against JSON::Tiny. It is a drop-in replacement for JSON::Tiny’s from-json and to-json subs, but it offers a few extra features.

Currently it seems to be about 4x faster and uses up about a quarter of the RAM JSON::Tiny would use.

This module also includes a very fast to-json function that tony-o created and lizmat later completely refactored.

Exported subroutines


    my $*JSON_NAN_INF_SUPPORT = 1; # allow NaN, Inf, and -Inf to be serialized.
    say to-json [<my Raku data structure>];
    say to-json [<my Raku data structure>], :!pretty;
    say to-json [<my Raku data structure>], :spacing(4);

enum Blerp <Hello Goodbye>;
say to-json [Hello, Goodbye]; # ["Hello", "Goodbye"]
say to-json [Hello, Goodbye], :enums-as-value; # [0, 1]

Encode a Raku data structure into JSON. Takes one positional argument, which is a thing you want to encode into JSON. Takes these optional named arguments:


Bool. Defaults to True. Specifies whether the output should be "pretty", human-readable JSON. When set to false, will output json in a single line.


Int. Defaults to 2. Applies only when pretty is True. Controls how much spacing there is between each nested level of the output.


Bool, defaults to False. Specifies whether keys from objects should be sorted before serializing them to a string or if $obj.keys is good enough.


Bool, defaults to False. Specifies whether enums should be json-ified as their underlying values, instead of as the name of the enum.


    my $x = from-json '["foo", "bar", {"ber": "bor"}]';
    say $x.perl;
    # outputs: $["foo", "bar", {:ber("bor")}]

Takes one positional argument that is coerced into a Str type and represents a JSON text to decode. Returns a Raku datastructure representing that JSON.


Bool. Defaults to False. Specifies whether Hashes and Arrays should be rendered as immutable datastructures instead (as Map / List. Creating an immutable data structures is mostly saving on memory usage, and a little bit on CPU (typically around 5%).

This also has the side effect that elements from the returned structure can now be iterated over directly because they are not containerized.

    my %hash := from-json "META6.json".IO.slurp, :immutable;
    say "Provides:";
    .say for %hash<provides>;

Additional features

Adapting defaults of "from-json"

In the use statement, you can add the string "immutable" to make the default of the immutable parameter to the from-json subroutine True, rather than False.

    use JSON::Fast <immutable>;  # create immutable data structures by default

Adapting defaults of "to-json"

In the use statement, you can add the strings "!pretty", "sorted-keys" and/or "enums-as-value" to change the associated defaults of the to-json subroutine.

    use JSON::FAST <!pretty sorted-keys enums-as-value>;

Strings containing multiple json pieces

When the document contains additional non-whitespace after the first successfully parsed JSON object, JSON::Fast will throw the exception X::JSON::AdditionalContent. If you expect multiple objects, you can catch that exception, retrieve the parse result from its parsed attribute, and remove the first rest-position characters off of the string and restart parsing from there.