prefix-expression

Library to Evaluate Prefix Expressions represented in JSON

npm i prefix-expression

Overview

prefix expression can be represented in JSON Format as follows

EXPRESSION = {
    OPERATOR : [
        ...OPERANDS
    ]
}

An OPERAND can be strng, number, boolean, null, array or EXPRESSION The type and number of OPERANDs are defined by each operator

The supported OPERATORs are

• Numeric
  • Arithmatic
    ( +, -, *, /, pow, % )
  • Comparision
    ( >, >=, <, <= )
• Boolean Logic
  • Comparision
    ( ==, ===, !=, !== )
  • Negate
    ( ! )
  • Logical
    ( or, and )
  • Others
    ( if ) if requires 3 operands [condition, trueValue, falseValue]
• Array
  • ( map, reduce, filter )
  • ( intersection, diff, union )
  • ( includes )
  • ( size ) works with string also
  • ( max, min )
• String
  • ( indexOf )
  • ( concat )
  • ( size ) works with array also
• Object
  • ( entries )
• Special Operators
  Special Operators can not be overrided or removed
  • Data Access
    ( var )
    Uses JSONPath to access data
    has 2 operands , 1st is a JSON path string or an expression which resolves into a string , 2nd is boolean indicating to return all or 1st result from json path query
  • Callback
    ( callback )
    to differ the evaluation of expression until parent expression is evaluated ... parent Operation can use the callback to evaluate child expression with new data

Install

npm i prefix-expression

Usage

evaluate

import { evaluate, PrefixExpression, Expression } from "prefix-expression"

// prefix expression
const expression: PrefixExpression;

// simple evaluate
const result = evaluate(expression);

// evaluate with data
const data: unknown;
const result = evaluate(expression, data);

// overide the operators
type OperatorLogic = {
  name: string;
  logic: {
    schema: JSONSchemaType<Expression[]>;
    operation: (operands: Expression)=>Expression};
}
const operators: (string|OperatorLogic)[];
const result = evaluate(expression, {}, operators);

• result is either result of the expression OR reduced expression with unresolved data
• result can be still evaluated when more data is available

Support

This project is a part of Open Source Intitiative from Sodaru Technologies

Write an email to [email protected] for queries on this project