Background

Trees are everywhere in computing, representing more complex than a list or sequence. The former is two dimensional, while the other is linear or one dimensional.

Examples of trees in computing:

• JSON
• XML documents
• Computer languages

Before expanding on their utility consider the following key classes/interfaces.

Expression

An agnostic AST that supports complex expressions, including computation, logical operands and invoking user defined functions.

• Immutable
• Functional
• Fully traversable
• May be evaluated - see below

ExpressionNumber

An abstraction holding a number value within an Expression, which available choices including:

• BigDecimal slower but more precision and various Rounding options.
• double faster but limited 64-bit precision
• float fastest but limited 32-bit precision TODO

ExpressionEvaluationContext

A context accompanies the evaluation of an Expression and provides context aware values and behaviours.

• A powerful construct that supports many values and behaviours that modify evaluation of an expression.
• Provides the preferred ExpressionNumber to use at evaluation time, during number / calculations.

Extends LocaleContext, which provides locale aware values such as decimal point, currency, day names and more.

ExpressionFunction

A function provides an independent function which describes

• name The name, which is used within expressions.
• return type The return type
• parameters All the parameters including their name, cardinality and type.
• purity Useful to determine whether the computed value can be cached, Within a spreadsheet this can help improve speed by avoiding unnecessary recalculations, because component values have or will never change.

ExpressionFunction(s)

• basic
• currency
• currencyCode
• currencyValue
• expression
• expressionNumberFunction
• eval
• fake
• lambda
• list
• listNonNull
• locale
• localeLanguageTag
• node
• nodeName
• nullFunction
• typeName

The accompanying ExpressionEvaluationContext when executing a function uses the function metadata to convert values to the target type as necessary, supporting a type-safe but dynamic conversions as necessary.

Projects

The following function projects hold many functions, and can be used in any Expression context including Spreadsheets.

• boolean
• datetime
• engineering
• net
• number
• number-trigonometry
• spreadsheet
• stat
• string
• walkingkooka-spreadsheet-expression-function Contains additional functions that can be executed within a spreadsheet expression context.

Node

A Node is a unit within a tree, coming in two forms, leaves and parent nodes with the former never having children while the later possibly containing zero or more children. Numerous Node implementations include:

• Expression
• File A file system abstraction, execute xpath over directories and files.
• Json Json objects.
• Patch JSON Patch
• Pojo Java POJOs with highlight support
• Xml Xml documents

Select

A selector represents a query which may be used to match Node within a node graph, equivalent to XPATH

• Almost identical in syntax and effective functionality to that of XPATH.
• May be executed using any of the many Node implementations.

NodePointer

A NodePointer supports path navigation/selection over a Node and is similar in syntax and features to JSON POINTER. Like Select is can operate against any of the above mentioned Node implementations.

NodePatch

A NodePatch is an equivalent technology similar to json-patch but supports all Node technologies.