README.md

Golang Rules Engine

Rules engine written in golang with the help of antlr.

This package will be very helpful in situations where you have a generic rule and want to verify if your values (specified using map[string]interface{}) satisfy the rule.

Here are some examples:

  parser.Evaluate("x eq 1", map[string]interface{}{"x": 1})
  parser.Evaluate("x == 1", map[string]interface{}{"x": 1})
  parser.Evaluate("x lt 1", map[string]interface{}{"x": 1})
  parser.Evaluate("x < 1", map[string]interface{}{"x": 1})
  parser.Evaluate("x gt 1", map[string]interface{}{"x": 1})

  parser.Evaluate("x.a == 1 and x.b.c <= 2", map[string]interface{}{
    "x": map[string]interface{}{
       "a": 1,
       "b": map[string]interface{}{
          "c": 2,
       },
    },
  })


  parser.Evaluate("y == 4 and (x > 1)", map[string]interface{}{"x": 1})

  parser.Evaluate("y == 4 and (x IN [1,2,3])", map[string]interface{}{"x": 1})

  parser.Evaluate("y == 4 and (x eq 1.2.3)", map[string]interface{}{"x": "1.2.3"})

Operations

All the operations can be written capitalized or lowercase (ex: eq or EQ can be used)

Logical Operations supported are and or

Compare Expression and their definitions

expression	meaning
eq	equals to
==	equals to
ne	not equal to
!=	not equal to
lt	less than
<	less than
gt	greater than
>	greater than
le	less than or equal to
<=	less than or equal to
ge	greater than or equal to
>=	greater than or equal to
co	contains
sw	starts with
ew	ends with
in	in a list
pr	present, will be true if you have a key as true
not	not of a logical expression

How to use it

Use your dependency manager to import github.com/nikunjy/rules/parser. This will let you parse a rule and keep the parsed representation around. Alternatively, you can also use github.com/nikunjy/rules directly to call the root Evaluate(string, map[string]interface{}) method.

I would recommend importing github.com/nikunjy/rules/parser

How to extend the grammar

1. Please look at this antlr tutorial, the link will show you how to setup antlr. The article has a whole lot of detail about antlr I encourage you to read it, you might also like my blog post about this repo.
2. After taking a look at the antlr tutorial, you can extend the JsonQuery.g4 file.
3. Compile the parser antlr4 -Dlanguage=Go -visitor -no-listener JsonQuery.g4 -o ./ (Note: -o is the output directory, make sure all the stuff it generates is in the parser directory of the root repo folder)