haystack-core

Haystack Core

A core haystack implementation written in TypeScript.

• Core haystack type implementation.
• Haystack filter compilation and evaluation.
• Core haystack units implementation.
• Hayson encoding/decoding.
• Zinc 3.0 encoding/decoding.
• Haystack v4 defs full normalization, namespace and filter support.
• Older Haystack version 3 JSON encoding.

This library is designed to be used in conjunction with these other haystack libraries depending on your use case...

• Haystack units: all haystack units.
• Haystack nclient: a client network library used for working with a haystack server.
• Haystack react: a set of high level React hooks and utilities for working with haystack data.

If you're after a high performance haystack library for running on constrained devices, please see libhaystack.

Installation

npm install haystack-core

APIs

Please click here for the API documentation.

Core Types

The following core Haystack types are implemented...

• HVal: the base class for all haystack values.
• HStr: a string value.
• HBool: a boolean true or false value.
• HNum: a numeric value.
• HCoord: co-ordinates with latitude and longitude.
• HXStr: an xstring implementation. Supports difference types and mime types.
• HDate: a date value.
• HTime: a time value.
• HDateTime: date and time.
• HSymbol: a symbol.
• HDict: dictionary - a map of key/haystack value pairs.
• HGrid: grid - a table of haystack values.
• HList: a list of haystack values.
• HMarker: a marker value.
• HNa: a non-applicable value.
• HRef: a reference value.
• HRemove: a remove value.
• HUri: a universal resource indicator value.

Each haystack value has a kind that can be queried. A haystack value can be encoded to Zinc by calling toZinc().

To convert a Zinc back to a haystack value see ZincReader.

Units

Haystack core has full support for units. The actual unit database implementation is stored in haystack-units. This enables a developer to import the whole unit database or just the units they're interested in working in.

Defs

Haystack core has comprehensive support for Haystack v4 defs. Defs add an ontology to the pre-existing haystack taxonomy that is now formalized.

• Normalization: compile a number of libraries (typically held in a trio format) into a normalized def database that can be consumed by a namespace.
• Namespace: the defs database that can be queried.
• Filter: extra haystack filter support for making semantic queries using defs.

Trio

The TrioReader and TrioWriter classes are used to read and write Trio files.

Hayson

Hayson is an alternative JSON encoding format for Haystack that's being promoted.

Hayson has full support in Haystack Core.

Shorthand

An abbreviated namespace of useful methods has been created to make it easier to work with in environments such as a web browser.

Filters

A full haystack filter compiler implementation is included.

To work with filters please see HFilter.

• Compile a haystack filter into a node AST (abstract syntax tree).
• Evaluate a Haystack Filter against some haystack values.
• Convert an AST Node tree back into a haystack filter.
• Build a filter using HFilterBuilder

Design

Grammar

For the full grammar, please see the class definition for the Parser.

The main class to work with is HFilter. This class contains a number of high level methods that hide the complexity of working with the underlying parser.

Nodes

When a haystack filter string is parsed, it's converted into an AST (abstract syntax tree) hierarchy of Nodes.

The Node tree can be used in the following ways...

• Locally evaluated against some data to see if the filter matches or not.
• Converted to back into a haystack filter string.
• Modified via the relevant accessor methods for each different type of Node.
• Revalidated to ensure any changes to the Node tree doesn't contain errors.

Visitors

The visitor design pattern has been implemented to make it easy to generate code for different targets (i.e. a haystack filter string).

LocalizedError

Any errors caught during parsing are thrown as LocalizedError objects. This error object contains a lexicon key and arguments used for localization as well as a possible index number. If the index number is defined, it will specify the index number of the character that caused the error in the original haystack filter.

Misc links

• Haystack zinc
• Haystack filters
• Java Haystack Filter implemenation