genruler 0.1.0

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ruler

A rule dsl language parser in Python

ruler DSL

This mini-language is partially inspired by LISP. A rule is represented by a an s-expression.

Syntax & Structure

(namespace.function_name "some_arguments" "more_arguments_if_applicable")

A rule is usually consist of a function name, and a list of (sometimes optional) arguments. Function names are often namespaced (e.g. "boolean.and", "condition.equal" etc.) and usually only recognized if placed in the first elemnt.

Unless otherwise specified, a rule can be inserted as an argument to another rule, for example a boolean.and rule.

(boolean.and (condition.equal (basic.field "fieldA") "X"),
              condition.equal (basic.field "fieldB") "Y")

Parsing and computing result

In order to parse the rule, just call genruler.parse. The result is a function where you can put in a context object in order for it to compute a result.

import genruler

rule = genruler.parse('(condition.Equal (basic.Field "fieldA") "X")')
context = {"fieldA": "X"}
rule(context) // should return true

Usage

Installation

I probably should submit this to PyPI so it is pip-installable

Ruler API overview

Array functions

Some array related functions.

array.length

(array.length $argument)

Returns the length of a given array $argument. For example,

import genruler

rule = genruler.parse('(array.length (basic.Field "fieldA"))')
context = {"fieldA": [1, 2, 3]}
rule(context) // should return 3

Basic functions

Some random functions that don't fit anywhere else goes here

basic.context

(basic.Context $context_sub, $rule)

Temporarily change the context to $context_sub, and perform $rule with $context_sub as the new context

• $context_sub (required): A struct, or a rule to extract a new struct w.r.t. the original context
• $rule (required): the rule to be applied w.r.t. $context_sub

An example:

rule = ruler.parse('(basic.Context (basic.field, 'sub')
                                   (basic.field, 'foo'))')

context = {"sub": {"foo": "bar"}}
rule(context) # returns context['sub']['foo'], which is 'bar'

Basic.field

(basic.field $key $default)

Returns a field value from context when called.

• $key (required): is a key in the context.
• $default (optional): is a default value to be returned when context[key] does not exist.

basic.value

(basic.value $value)

Returns a value, regardless what is in the context

• $value (required): a value to return. MAY NOT be a sub-rule

Boolean operators

Usually used to chain condition rules (see next section) together

boolean.and_

(boolean.and_ $argument1 $argument2 ...)

Returns True if all arguments returns True, or False otherwise.

boolean.contradiction

(boolean.contradiction)

Always returns a False, a shorthand for

(basic.Value false)

boolean.not_

(boolean.not_ $argument)

Returns the result of negation done to $argument.

boolean.or_

(boolean.or $argument2 $argument2)

Returns True if any of the arguments is True, or False otherwise.

boolean.tautology

(boolean.tautology)

Returns True regardless

Condition rules

Usually returns either true or false

condition.equal

(condition.equal $alpha $beta)

Returns True if and only if $alpha is equivalent to $beta.

condition.gt

(condition.gt $alpha $beta)

Returns True if and only if $alpha is greater than $beta.

condition.ge

(condition.ge $alpha $beta)

Returns True if and only if $alpha is greater than or equal to $beta.

condition.in_

(condition.In $alpha $values)

Returns True if $alpha is in $values

condition.is_none

(condition.is_none $alpha)

Returns True if $alpha is None

condition.is_true

(condition.Is_True $alpha)

Returns True if $alpha is True

condition.lt

(condition.less_than $alpha $beta)

Returns True if and only if $alpha is less than $beta.

condition.le

["condition.Less_Than_Equal", $alpha, $beta]

Returns True if and only if $alpha is less than or equal to $beta.

String operations

Some basic string operations

string.concat

(string.Concat $link $argument1 $argument2 ...)

Concatenate arguments by $link

string.concat_fields

(string.concat_fields $link $key1 $key2 ...)

A short hand for

(string.concat $link (string.Field $key1) (string.field $key2) ...)

Note: $key1, $key2 etc.

string.lower

(string.lower $value)

Change $value to lowercase