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https://github.com/propensive/merino

A JSON parser and AST
https://github.com/propensive/merino

fast-json-parser json-parser scala

Last synced: 12 months ago
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A JSON parser and AST

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# Merino

jawn



__A fast JSON parser for Scala.__



_Merino_ is a JSON parser, and nothing more. It provides just a single `parse`

method that reads a stream of bytes and returns structured data.



## Features



- bare-bones JSON parsing

- provides a single `parse` method

- produces "raw" output, mostly as primitive types

- optimized for performance



## Availability



## Getting Started



Merino will parse a `DataStream`, that is, a `LazyList[IArray[Byte]]`. This

makes it easy to parse any type which can be converted to a byte array or a

lazy stream.



The `JsonAst.parse` method will parse the input and return a `JsonAst`, which

is an opaque type alias for the union of the following types:

- `Long`, `Double` and `BigDecimal`, representing JSON number types,

- `String` for JSON strings,

- `Boolean` for JSON `true` and `false` values,

- `Null` for the `null` value,

- `IArray[Any]` representing a JSON array, and,

- `(IArray[String], IArray[Any])` representing a JSON object



Note that which type of `Long`, `Double` or `BigDecimal` the parser chooses to

represent a given number will be determined by whether the type can represent

the number, as specified in the JSON source, precisely.



The types `IArray[Any]` and `(IArray[String], IArray[Any])`, representing

arrays and objects, will only ever contain `JsonAst`-typed values, despite

having type parameters of `Any`. But type aliases cannot refer to themselves,

so `Any` is used instead.



Additionally, the type `(IArray[String], IArray[Any])` was chosen as an

alternative to `IArray[(String, Any)]` since the former requires `2n + 3`

objects to be constructed for each field in the JSON object, as opposed to

`3n + 1` in the latter case: for anything but an object of exactly one key, the

former requires fewer objects to be created. Additionally, the types may be

disambiguated reflectively by their erased types.



If parsing fails, a `JsonParseError` will be thrown, including the line and

column in which the error occurs, and an enumeration value (of type

`JsonParseError.Issue`) describing the error.



## Status



Merino

jawn is classified as __maturescent__. For reference, Soundness projects are

categorized into one of the following five stability levels:



- _embryonic_: for experimental or demonstrative purposes only, without any guarantees of longevity

- _fledgling_: of proven utility, seeking contributions, but liable to significant redesigns

- _maturescent_: major design decisions broady settled, seeking probatory adoption and refinement

- _dependable_: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version `1.0.0` or later

- _adamantine_: proven, reliable and production-ready, with no further breaking changes ever anticipated



Projects at any stability level, even _embryonic_ projects, can still be used,

as long as caution is taken to avoid a mismatch between the project's stability

level and the required stability and maintainability of your own project.



Merino

jawn is designed to be _small_. Its entire source code currently consists

of 825 lines of code.



## Building



Merino

jawn will ultimately be built by Fury, when it is published. In the

meantime, two possibilities are offered, however they are acknowledged to be

fragile, inadequately tested, and unsuitable for anything more than

experimentation. They are provided only for the necessity of providing _some_

answer to the question, "how can I try Merino

jawn?".



1. *Copy the sources into your own project*

   

   Read the `fury` file in the repository root to understand Merino

jawn's build

   structure, dependencies and source location; the file format should be short

   and quite intuitive. Copy the sources into a source directory in your own

   project, then repeat (recursively) for each of the dependencies.



   The sources are compiled against the latest nightly release of Scala 3.

   There should be no problem to compile the project together with all of its

   dependencies in a single compilation.



2. *Build with [Wrath](https://github.com/propensive/wrath/)*



   Wrath is a bootstrapping script for building Merino

jawn and other projects in

   the absence of a fully-featured build tool. It is designed to read the `fury`

   file in the project directory, and produce a collection of JAR files which can

   be added to a classpath, by compiling the project and all of its dependencies,

   including the Scala compiler itself.

   

   Download the latest version of

   [`wrath`](https://github.com/propensive/wrath/releases/latest), make it

   executable, and add it to your path, for example by copying it to

   `/usr/local/bin/`.



   Clone this repository inside an empty directory, so that the build can

   safely make clones of repositories it depends on as _peers_ of `merino

jawn`.

   Run `wrath -F` in the repository root. This will download and compile the

   latest version of Scala, as well as all of Merino

jawn's dependencies.



   If the build was successful, the compiled JAR files can be found in the

   `.wrath/dist` directory.



## Contributing



Contributors to Merino

jawn are welcome and encouraged. New contributors may like

to look for issues marked

[beginner](https://github.com/propensive/merino

jawn/labels/beginner).



We suggest that all contributors read the [Contributing

Guide](/contributing.md) to make the process of contributing to Merino

jawn

easier.



Please __do not__ contact project maintainers privately with questions unless

there is a good reason to keep them private. While it can be tempting to

repsond to such questions, private answers cannot be shared with a wider

audience, and it can result in duplication of effort.



## Author



Merino

jawn was designed and developed by Jon Pretty, and commercial support and

training on all aspects of Scala 3 is available from [Propensive

OÜ](https://propensive.com/).



## Name



Merino is named after the variety of sheep known for the quality of their fleeces, in keeping with the trend for

JSON libraries to allude to the story of Jason and the Argonauts.



In general, Soundness project names are always chosen with some rationale,

however it is usually frivolous. Each name is chosen for more for its

_uniqueness_ and _intrigue_ than its concision or catchiness, and there is no

bias towards names with positive or "nice" meanings—since many of the libraries

perform some quite unpleasant tasks.



Names should be English words, though many are obscure or archaic, and it

should be noted how willingly English adopts foreign words. Names are generally

of Greek or Latin origin, and have often arrived in English via a romance

language.



## Logo



The logo represents a ball of wool, potentially merino wool.



## License



Merino

jawn is copyright © 2025 Jon Pretty & Propensive OÜ, and

is made available under the [Apache 2.0 License](/license.md).