Working with Expressions

Expressions are widely used throughout Iotellect, so it's sometimes quite important to handle expression processing programmatically.

An expression is represented by Expression class that can be constructed from a string. However, instances of Expression encapsulate a parsed syntax tree. Thus, if a single Expression is evaluated multiple times (e.g. with different environment), parsing of its source text is performed only once.

Expression evaluation, e.g. calculation of results, is performed by evaluate() methods of Evaluator class. Those methods return raw Object instances representing resulting values. However, there are also methods involving conversion of resulting value to a certain type: evaluateToBoolean(), evaluateToColor(), evaluateToData(), evaluateToDataTable(), evaluateToDate(), evaluateToNumber(), evaluateToString() and more.

The Evaluator object has a map of reference schema that is used to determine which part of the system should be used to resolve a references. The most commonly used schema indicate the standard reference (where no schema is specified) and the environment reference, indicated with the env schema.

The majority of expressions requires a certain schema to be specified, so the Evaluator class has a number of special constructors and configuration methods delegating functionality to the standard schema and allowing to specify:

  • The ContextManager that will be used to find contexts.

  • Default Context.

  • Default DataTable.

  • CallerController that replicates the permissions of the user or module for which the expression is being evaluated.

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