imicros-feel-interpreter

FEEL interpreter written in JavaScript.

Developed for of the imicros backend, but can be used also stand-alone.

Installation

$ npm install imicros-feel-interpreter

Usage

const { Interpreter } = require("imicros-feel-interpreter");

const interpreter = new Interpreter();

/*** parse and evaluate in a single step ***/
let result = interpreter.evaluate("a/b**-c-d",{a:1,b:2,c:4,d:3});
// 13

/*** or in two steps: parse single evaluate multiple***/
let success = interpreter.parse("a/b**-c-d");
// true

let serialized = JSON.stringify(interpreter.ast);
interpreter.ast = JSON.parse(serialized);
// serialized ast can be stored somewhere and restored for multiple usage with different data sets

let result = interpreter.evaluate({a:1,b:2,c:4,d:3});
// 13

Usage Converter to convert a DMN file (XML) to a single FEEL expression

const { DMNParser, DMNConverter } = require("imicros-feel-interpreter");
const fs = require("fs");

const xmlData = fs.readFileSync(./assets/Sample.dmn).toString();
const expression = new DMNConverter().convert({ xml: xmlData });

Features

• Complete support of DMN 1.4. Known restrictions see below.
• Provide build-in functions as listed below.

Restrictions

• Additional name symbols ./-+* according rule 30. of the sepcification as well as keywords for,return,if,true,false,in,and,or,between,some,every,then,else,not,string,number,boolean,null,date,time,duration in names are not supported. (The package uses nearley as parser and I didn't found a way to implement the ambiguity). White spaces are allowed and normalized (doubled spaces will be replaced by just one space). Therefore expresssions like {"new example": 5}.new    example as well as { "new     example": 5}.new example will work. Beside white spaces the special characters _?' which are not used as operators are allowed.
• No external functions are supported.

Performance considerations

In case of intensive usage with large number of data sets consider the pre-parsing possibility.

A simple expression if even(i) then (i*a) else (i*b) with parsing and evaluation in one step evaluates 2.500 data sets per second and with a single parsing you can evaluate up to 200.000 data sets per second on an average hardware with single thread processing.

Example expressions

• date and time("2022-04-05T23:59:59") < date("2022-04-06") w/o context --> true
• if a>b then c+4 else d with context {a:3,b:2,c:5.1,d:4} --> 9.1
• {"Mother's finest":5, "result": 5 + Mother's finest}.result --> 10
• "best of " + lower case("IMicros") w/o context --> "best of imicros"
• [{a:3,b:1},{a:4,b:2}][item.a > 3] w/o context --> [{a:4,b:2}]
• [1,2,3,4,5,6,7,8,9][a*(item+1)=6] with context {a:2} --> [2]
• a+b > c+d with context {a:5,b:4,c:3,d:5} --> true
• flight list[item.status = "cancelled"].flight number with context {"flight list": [{ "flight number": 123, status: "boarding"},{ "flight number": 234, status: "cancelled"}]} --> [234]
• {calc:function (a:number,b:number) a-b, y:calc(b:c,a:d)+3}.y with context {c:4,d:5} --> 4
• deep.a.b + deep.c with context {deep:{a:{b:3},c:2}} --> 5
• {a:3}.aw/o context --> 3
• extract("references are 1234, 1256, 1378", "12[0-9]*") w/o context --> ["1234","1256"]
• (a+b)>(8.9) and (c+d)>(8.1) with context {a:5,b:4,c:4,d:5}--> true
• @"2022-04-10T13:15:20" + @"P1M" w/o context --> "2022-05-10T13:15:20"
• day of year(@"2022-04-16") w/o context --> 106
• @"P7M2Y" + @"P5D" w/o context --> "P5D7M2Y"
• { "PMT": function (p:number,r:number,n:number) (p*r/12)/(1-(1+r/12)**-n), "MonthlyPayment": PMT(Loan.amount, Loan.rate, Loan.term) + fee }.MonthlyPayment with context {Loan: { amount: 600000, rate: 0.0375, term:360 }, fee: 100} --> 2878.6935494327668
• decision table( outputs: ["Applicant Risk Rating"], inputs: ["Applicant Age","Medical History"], rule list: [ [>60,"good","Medium"], [>60,"bad","High"], [[25..60],-,"Medium"], [<25,"good","Low"], [<25,"bad","Medium"] ], hit policy: "Unique" ) with context {"Applicant Age": 65, "Medical History": "bad"} --> { "Applicant Risk Rating": "High" }

Supported expressions

(not the complete list - refer to the test cases for a complete list of tested expressions)

Arithmetic

Muliplication: *, Division: /, Addition: +, Subtraction: -, Exponentation: **

• (x - 2)**2 + 3/a - c*2

Negation: -

• -5

Boolean

And: and, Or: or

Equal to: =, not equal to: !=, less than: <, less than or equal to: <=, greater than: >, greater than or equal to: >=

• 5 = 5 and 6 != 5 and 3 <= 4 and date("2022-05-08") > date("2022-05-07") --> true

Existence check: is defined(var)

• is defined({x:null}.x) --> true
• is defined({}.x) --> false

Negation: not(expression)

• {a:5,b:3,result: not(a<b)}.result --> true

Type check: expression instance of type

• a instance of b with context {a:3,b:5} --> true
• a instance of string with context {a:"test"} --> true
• a instance of number with context {a:3} --> true
• a instance of boolean with context {a:true} --> true

String

Concatenate: + (only possible with both terms type string)

• "foo" + "bar" --> "foobar"

Context and path

Context is a defintion in JSON notation with { key: value }.
The key must evaluate to a string, the value can be any expression (including function definitions and complete decision table calls).
With the .name notation an attribute of the context is accessed.

• {a:3}.a --> 3
• deep.a.b + deep.c with context {deep:{a:{b:3},c:2}} --> 5
• {calc:function (a:number,b:number) a-b, y:calc(b:c,a:d)+3}.y with context {c:4,d:5} --> 4
• {calc:function (a:number,b:number) a+b, y:calc(4,5)+3} --> {y:12}

Filter (Lists)

Get element by index (index count is starting with 1)

• [1,2,3,4][2] --> 2

Negative indices are counted from the end

• [1,2,3,4][-1] --> 3
• [1,2,3,4][-0] --> 4

Reduce list based on logic expression - variable item is the current element

• [1,2,3,4][item > 2] --> [3,4]
• [1,2,3,4,5,6,7,8,9][a*(item+1)=6] with context {a:2} --> [2]
• [1,2,3,4][even(item)] --> [2,4]
• flight list[item.status = "cancelled"].flight number with context {"flight list": [{ "flight number": 123, status: "boarding"},{ "flight number": 234, status: "cancelled"}]} --> [234]

Temporal

Date or date and time expressions as well as durations can be written with the @String notation

• @"2022-05-10T13:15:20" - @"P1M" --> "2022-04-10T13:15:20"
• @"13:45:20" - @"PT30M" --> "13:15:20"
• date("2022-05-14") - date("2020-09-10") --> "P4D8M1Y"
• date("2020-09-10")-date("2022-05-14") --> "-P4D8M1Y"

Comparison with <,<=,>,>=,=
Additon/Subtraction with date|date and time +/- duration

• date("2022-04-05") < date("2022-04-06") --> true
• date and time("2022-04-15T08:00:00") = date and time("2022-04-15T00:00:00") + @"P8H" --> true
• @"P5D" > @"P2D" --> true
• @"P5D" > @"P4DT23H" --> true

Comparison with in interval

• date("2022-04-05") in [date("2022-04-04")..date("2022-04-06")] --> true
• (date("2022-04-01")+duration("P3D")) in [date("2022-04-04")..date("2022-04-06")] --> true

Comparison with between date|date and time and date|date and time

• date("2022-04-05") between date("2022-04-04") and date("2022-04-06") --> true

Access of attributes of the temporal type

• @"2022-04-10".month --> 4
• date("2022-04-10").day --> 10
• date and time("2022-04-10T13:15:20").year --> 2022
• date and time("2022-04-10T13:15:20").hour --> 13
• date and time("2022-04-10T13:15:20").minute --> 15
• date and time("2022-04-10T13:15:20").second --> 20
• @"P12D5M".months --> 5
• today().year --> current year
• now().minute --> current minute
• day of week(@"2022-04-16") --> "Saturday"
• day of year(@"2022-04-16") --> 106
• week of year(@"2022-04-16") --> 15
• abs(@"-P7M2Y") --> "P7M2Y"

If

if condition then expression else expression

• if 1 > 2 then 3 else 4

For

for name in iteration context return expression

• for a in [1,2,3] return a*2 --> [2,4,6]

Comments

single line comments starting with // until the end of the line single line or multiline comments framed with /* and */.

/*  start 
    comment */ 
decision table(
    outputs: ["Applicant Risk Rating"],  
    inputs: ["Applicant Age","Medical History"],
    /* multi line
        between */
    rule list: [
        [>60,"good","Medium"],
        [>60,"bad","High"],
        [[25..60],-,"Medium"],
        /**** 
         * important comment 
         ****/
        [<25,"good","Low"],
        [<25,"bad","Medium"] // single line comment
    ],
    hit policy: "Unique"
) /* end comment */

Supported build-in functions

Conversion

• date(from|year,month,day)
• time(from|hour,minute,second,offset?) with offset type duration (e.g. @"PT1H")
• missing: date and time(from - with named parameter|date,time)
• years and months duration(from,to) with from,to type date
• number(from) with from type string
• string(from)
• context(entries) with entries type object with attributes key and value (e.g. {key: "a",value: 1})

Temporal

• today()
• now()
• day of week(date)
• day of year(date)
• week of year(date)
• month of year(date)
• abs(duration)

Arithmetic

• decimal(n,scale)
• floor(n)
• ceiling(n)
• round up(n,scale?)
• round down(n,scale?)
• round half up(n,scale?)
• round half down(n,scale?)
• abs(number)
• modulo(dividend,divisor)
• sqrt(number)
• log(number)
• exp(number)
• odd(number)
• even(number)

Logical

• is defined(value)
• not(negand)

Ranges

• before(a,b) with a,b either point or interval
• after(a,b) with a,b either point or interval
• meets(a,b) with a,b intervals
• met by(a,b) with a,b intervals
• overlaps(a,b) with a,b intervals
• overlaps before(a,b) with a,b intervals
• overlaps after(a,b) with a,b intervals
• finishes(a,b) with a eiter point or interval and b interval
• finished by(a,b) with a interval and b either point or interval
• includes(a,b) with a interval and b either point or interval
• during(a,b) with a eiter point or interval and b interval
• starts(a,b) with a eiter point or interval and b interval
• started by(a,b) with a interval and b either point or interval
• coinsides(a,b) with a,b either both points or both intervals

Lists

• list contains(list,element)
• count(list) / count(...item)
• min(list) / min(...item)
• max(list) / max(...item)
• sum(list) / sum(...item)
• product(list) / product(...item)
• mean(list) / mean(...item)
• median(list) / median(...item)
• stddev(list) / stddev(...item)
• mode(list) / mode(...item)
• all(list) / all(...item)
• and(list)
• any(list) / any(...item)
• or(list)
• sublist(list, startposition, length?)
• append(list,...item)
• union(...list)
• concatenate(...list)
• insert before(list,position,newItem)
• remove(list,position)
• reverse(list)
• index of(list,match)
• distinct values(list)
• flatten(list)
• sort(list,precedes)
• string join(list,delimiter?,prefix?,suffix?)

Strings

• substring(string,start,length)
• string length(string)
• upper case(string)
• lower case(string)
• substring before(string,match)
• substring after(string,match)
• contains(string,match)
• starts with(string,match)
• ends with(string,match)
• matches(input,pattern)
• replace(input,pattern,replacement,flags)
• split(string,delimiter)
• extract(string,pattern)

Context

• get value(context,key)
• get entries(context)
• put(context,key,value)
• put all(entries)

Decisions

• boxed expression(context,expression)
• decision table(output, input, rule list, hit policy) (supported hit policies: "U"|"Unique","A"|"Any","F"|"First","R"|"Rule order","C"|"Collect","C+"|"C<"|"C>"|"C#")

Complete (complex) decisions

Also complex decisions like the example under assets/Sample.dmn can be written as a complex FEEL expression and evaluated - here for example as a context returning the last evaluated context entry.

const Interpreter = require("../lib/interpreter.js");

const interpreter = new Interpreter();

let exp = `
{   "Lender Acceptable DTI": function () 0.36,
    "Lender Acceptable PITI": function () 0.28,
    "DTI": function (d,i) d/i,
    "PITI": function (pmt,tax,insurance,income) (pmt+tax+insurance)/income,
    "Credit Score.FICO": Credit Score.FICO,
    "Credit Score Rating": decision table(
            inputs: ["Credit Score.FICO"],
            outputs: ["Credit Score Rating"],
            rule list: [
                [>=750,"Excellent"],
                [[700..750),"Good"],
                [[650..700),"Fair"],
                [[600..650),"Poor"],
                [< 600,"Bad"]
            ],
            hit policy: "U"
        ).Credit Score Rating,
    "Client DTI": DTI(d: Applicant Data.Monthly.Repayments + Applicant Data.Monthly.Expenses, i: Applicant Data.Monthly.Income),
    "Client PITI": PITI(
        pmt: (Requested Product.Amount*((Requested Product.Rate/100)/12))/(1-(1/(1+(Requested Product.Rate/100)/12)**-Requested Product.Term)),
        tax: Applicant Data.Monthly.Tax,
        insurance: Applicant Data.Monthly.Insurance,
        income: Applicant Data.Monthly.Income
    ),
    "Back End Ratio": if Client DTI <= Lender Acceptable DTI()
        then "Sufficient"
        else "Insufficient",
    "Front End Ratio": if Client PITI <= Lender Acceptable PITI()
                    then "Sufficient"
                    else "Insufficient",
    "Loan PreQualification": decision table(
                    outputs: ["Qualification","Reason"],
                    inputs: ["Credit Score Rating","Back End Ratio","Front End Ratio"],
                    rule list: [
                        [["Poor","Bad"],-,-,"Not Qualified","Credit Score too low."],
                        [-,"Insufficient","Sufficient","Not Qualified","Debt to income ratio is too high."],
                        [-,"Sufficient","Insufficient","Not Qualified","Mortgage payment to income ratio is too high."],
                        [-,"Insufficient","Insufficient","Not Qualified","Debt to income ratio is too high AND mortgage payment to income ratio is too high."],
                        [["Fair","Good","Excellent"],"Sufficient","Sufficient","Qualified","The borrower has been successfully prequalified for the requested loan."]
                    ],
                    hit policy: "F"
                )
}.Loan PreQualification
`
let success = interpreter.parse(exp);
if (!success) console.log(interpreter.error);

result = interpreter.evaluate(exp,{
    "Credit Score": { FICO: 700 }, 
    "Applicant Data": { Monthly: { Repayments: 1000, Tax: 1000, Insurance: 100, Expenses: 500, Income: 5000 } },
    "Requested Product": { Amount: 600000, Rate: 0.0375, Term: 360 }
});

console.log(result);
// {
//   Qualification: 'Qualified',
//   Reason: 'The borrower has been successfully prequalified for the requested loan.'
// }