Simple (Expression and Rule) Engine

This is a simple engine for parsing and interpreting expressions and rules.

Install

add dependency at package.json, then install

"dependencies": {
  "simple-expr-engine": "git+https://github.com/luo3house/simple-expr-engine"
}

npm install
# or if use yarn
yarn

UMD

Directly use UMD with global variable simple_expr_engine:

https://github.com/luo3house/simple-expr-engine/tree/master/dist/umd/index.min.js

Expression Grammar

It is described as a JavaScript-like language. But not all features as JavaScript.

Space Splitted

( 1 != 0 )
( "hello world" == "hello world" )

Nested Expression and Auto Merge

( ( true == true ) and ( 0 == 1 ) )
( ( true == true ) and ( 0 == 1 ) or ( "hello" != "world" ) )

Weak Typing

( true == true )
( 1 == true )
( "strings that length > 1" == true )
( 0 == false )
( 50 < "100" )

Variable Injection

( order_status == OrderStatus_CREATED )
( pm25 > 80 )
( pm25 <= 80.80 )
( level > 60 )

Rule Grammar

Rule is described as A Group Of Expressions With Results.

The first matched expression will be returned from it's result, which interpreted to value true.

Here is an example:

( false == true ) => 0
( 0 == 1 ) => 1
( "hello" == "world" ) => 2
( true == true ) => 3
( true != true ) => 4

The rule above will result in 3 if interpreted.

Also, you can use variable instead.

( exp < 7 ) => 1
( exp < 16 ) => 2
( exp < 27 ) => 3
( exp < 40 ) => 4
( exp < 55 ) => 5
( exp < 72 ) => 6
( exp < 91 ) => 7
( exp < 112 ) => 8
( exp < 135 ) => 9
( exp < 160 ) => 10

interpret the rule above with variable exp = 150, you can get the level 9.

Use library

Interpret Expression

// configure variable pool
const context = {
  variableStore: new VariableStore([]),
};
// source code of expression
const source = `( true == true )`;
// parse
const expr = Facade.buildExpr(context, source);
// interpret
Interpreter.interpretExpr(expr); // true

with variables:

const context = {
  variableStore: new VariableStore([
    Variable.defineNUMBER('exp', 150),
  ]),
};
const source = `( exp == 150 )`;
const result = Interpreter.interpretExpr(
  Facade.buildExpr(context, source)
); // true

Interpret Rule

const context = {
  variableStore: new VariableStore([
    Variable.defineNUMBER('exp', 150),
  ]),
};
const sources = [
  "( exp < 7 ) => 1",
  "( exp < 16 ) => 2",
  "( exp < 27 ) => 3",
  "( exp < 40 ) => 4",
  "( exp < 55 ) => 5",
  "( exp < 72 ) => 6",
  "( exp < 91 ) => 7",
  "( exp < 112 ) => 8",
  "( exp < 135 ) => 9",
  "( exp < 160 ) => 10",
];
try {
  const result = Interpreter.interpretRules(
    Facade.buildRules(context, sources)
  ); 
  const level = result.valueHolder.asNumber() // 9
} catch (e: NoRuleResultError) {
  // throw if no any rules matched
}

To see more examples. Please visit __test__ dir.