Function in Grule

Built-In Functions

Built-in functions are all defined within the ast/BuiltInFunctions.go file. As of now, they are:

MakeTime(year, month, day, hour, minute, second int64) time.Time

MakeTime will create a time.Time with local locale.

Arguments

year is the Year number.
month is the Month number, January = 1.
day is the day number in a month.
hour the hour of the day starting from 0.
minute the minute of the hour starting from 0.
second the second of the minute starting from 0.

Returns

time.Time value representing the time as specified in the argument in local locale.

Example

rule SetExpire "Set the expire date for Fact created before 2020" {
    when
       Fact.CreateTime < MakeTime(2020,1,1,0,0,0)
    then
       Fact.ExpireTime = MakeTime(2021,1,1,0,0,0);
}

Changed(variableName string)

Changed will ensure the specified variableName is removed from the working memory before the next cycle.

Arguments

variableName the variable name to be removed from working memory.

Example

rule SetExpire "Set new expire date" {
    when
        IsZero(Fact.ExpireTime)
    then
        Fact.CalculateExpire(); // this function will internally change the ExpireTime variable
        Changed("Fact.ExpireTime")
}

Now() time.Time

Now function will create a new time.Time value containing the current time.

Returns

time.Time value representing the current value

Example

rule ResetTime "Reset the lastUpdate time" {
    when
        Fact.LastUpdate < Now()
    then
        Fact.LastUpdate = Now();
}

Log(text string)

Log will emit a log-debug string from within the rule.

Arguments

text The text to emit into the Log-Debug

Example

rule SomeRule "Log candidate name if he is below 17 years old" {
    when
        Candidate.Age < 17
    then
        Log("Under aged: " + Candidate.Name);
}

IsNil(i interface{}) bool

IsNil will check if the argument is a nil value.

Arguments

i a variable to check.

Returns

true if the specified argument isnil or an invalid ptr value.
false if the specified argument is a valid ptr value.

Example

rule CheckEducation "Check candidate's education fact" {
    when
        IsNil(Candidate.Education) == false &&
        Candidate.Education.Grade == "PHD"
    then
        Candidate.Onboard = true;
}

IsZero(i interface{}) bool

IsZero will check any variable in the argument for its Zero status value. Zero means that the variable is newly defined and has not been assigned an initial value. This is usually applied to types like string, int64, uint64, bool, time.Time, etc.

Arguments

i a variable to check.

Returns

true if the specified argument is Zero.
false if the specified argument not Zero.

Example

rule CheckStartTime "Check device's starting time." {
    when
        IsZero(Device.StartTime) == true
    then
        Device.StartTime = Now();
}

Retract(ruleName string)

Retract will exclude the specified rule from the subsequent cycle evaluations. If a rule is retracted its when scope will not be evaluated on the next cycles after the call to Retract. The engine will automatically resets all rule back inplace when it starts again from the beginning.

Arguments

ruleName name of the rule to retract.

Example

rule CheckStartTime "Check device's starting time." salience 1000 {
    when
        IsZero(Device.StartTime) == true
    then
        Device.StartTime = Now();
        Retract("CheckStartTime");
}

GetTimeYear(time time.Time) int

GetTimeYear will extract the Year value of the time argument.

Arguments

time The time variable

Returns

Year value of the time.

Example

rule StartNewYearProcess "Check if it's a new year to restart new FinancialYear." salience 1000 {
    when
        GetTimeYear(Now()) != GL.FinancialYear
    then
        GL.CloseYear(GL.FinancialYear)
}

GetTimeMonth(time time.Time) int

GetTimeMonth will extract the Month value of the time argument.

Arguments

time The time variable

Returns

Month value of the time. 1 = January.

Example

// TODO: something's not right here. The description is copy/pasted from above
// but the condition/action doesn't make sense to me
rule StartNewYearProcess "Check if its a new year to restart new FinancialYear." salience 1000 {
    when
        isZero(Process.Month)
    then
        Process.Month = GetTimeMonth(Process.Month);
}

GetTimeDay(time time.Time) int

GetTimeDay will extract the Day of the month value of the time argument.

Arguments

time The time variable

Returns

Day of month value of the time.

Example

rule GreetEveryDay "Log a greeting every day." salience 1000 {
    when
        Greeting.Day != GetTimeDay(Now())
    then
        Log("Its a new Day !!!")
        Retract("GreetEveryDay")
}

GetTimeHour(time time.Time) int

GetTimeHour will extract the Hour value of the time argument.

Arguments

time The time variable

Returns

Hour value of the time. Is between 0 to 23

Example

rule DailyCheckBuild "Execute build every 6AM and 6PM." {
    when
        GetTimeHour(Now()) == 6 || GetTimeHour(Now()) == 18
    then
        CiCd.BuildDaily();
        Retract("DailyCheckBuild");
}

GetTimeMinute(time time.Time) int

GetTimeMinute will extract the Minute value of the time argument.

Arguments

time The time variable

Returns

Minute value of the time, between 0 to 59

Example

rule DailyCheckBuild "Execute build every 6.30AM and 6.30PM." {
    when
        (GetTimeHour(Now()) == 6 || GetTimeHour(Now()) == 18) &&
        GetTimeMinute(Now()) == 30
    then
        CiCd.BuildDaily();
        Retract("DailyCheckBuild");
}

GetTimeSecond(time time.Time) int

GetTimeSecond will extract the Second value of the time argument.

Arguments

time The time variable

Returns

Second value of the time, between 0 to 59

Example

rule DailyCheckBuild "Execute build every 6.30AM and 6.30PM." {
    when
        (GetTimeHour(Now()) == 6 || GetTimeHour(Now()) == 18) &&
        GetTimeMinute(Now()) == 30 && GetTimeSecond(Now()) == 0
    then
        CiCd.BuildDaily();
        Retract("DailyCheckBuild");
}

IsTimeBefore(time, before time.Time) bool

IsTimeBefore will check if a time value precedes another time value.

Arguments

time The time value you wish to have checked
before The time value against which the above is checked

Returns

True if the before time value precedes the time value.
False if the before time value does not precede the time value.

Example

rule PromotionExpireCheck "Apply a promotion if promotion hasn't yet expired." {
    when
        IsTimeBefore(Now(), Promotion.ExpireDateTime)
    then
        Promotion.Discount = 0.10;
        Retract("PromotionExpireCheck");
}

IsTimeAfter(time, after time.Time) bool

IsTimeAfter will check if a time value follows another time value.

Arguments

time The time value you wish to have checked
after The time value against which the above is checked

Returns

True if the after time value follows time value.
False if the after time value does not follow the time value.

Example

rule AdditionalTax "Apply additional tax if new tax rules are in effect." {
    when
        IsTimeAfter(Purchase.TransactionTime, TaxRegulation.StartSince)
    then
        Purchase.Tax = Purchase.Tax + 0.01;
}

TimeFormat(time time.Time, layout string) string

TimeFormat will format a time argument as specified by layout argument.

Arguments

time The time value you wish to have formatted.
layout String variable specifying the date format layout.

For the layout format, you can read this article

Returns

A string formatted as specified.

Example

rule LogPurchaseDate "Log the purchase date." {
    when
        IsZero(Purchase.TransactionDate) == false
    then
        Log(TimeFormat(Purchase.TransactionDate, "2006-01-02T15:04:05-0700");
}

Complete()

Complete will cause the engine to stop processing further rules in its current cycle. This is useful if you want to terminate further rule evaluation under a set condition.

Example

rule DailyCheckBuild "Execute build at 6.30AM and 6.30PM." {
    when
        (GetTimeHour(Now()) == 6 || GetTimeHour(Now()) == 18) &&
        GetTimeMinute(Now()) == 30 && GetTimeSecond(Now()) == 0
    then
        CiCd.BuildDaily();
        Complete();
}

Math Functions

All the functions bellow is a wrapper to their golang math functions. You should read Golang math page to know how to use each function.

Unlike go, you don't have to use the math. prefix to use them in your GRL.

Use them like normal built in function.

when 
    Max(Fact.A, Fact.C, Fact.B) > 10
then
    Fact.X = Acosh(Fact.C);

Max(vals ...float64) float64
Min(vals ...float64) float64
Abs(x float64) float64
Acos(x float64) float64
Acosh(x float64) float64
Asin(x float64) float64
Asinh(x float64) float64
Atan(x float64) float64
Atan2(y, x float64) float64
Atanh(x float64) float64
Cbrt(x float64) float64
Ceil(x float64) float64
Copysign(x, y float64) float64
Cos(x float64) float64
Cosh(x float64) float64
Dim(x, y float64) float64
Erf(x float64) float64
Erfc(x float64) float64
Erfcinv(x float64) float64
Erfinv(x float64) float64
Exp(x float64) float64
Exp2(x float64) float64
Expm1(x float64) float64
Float64bits(f float64) uint64
Float64frombits(b uint64) float64
Floor(x float64) float64
Gamma(x float64) float64
Hypot(p, q float64) float64
Ilogb(x float64) int
IsInf(f float64, sign int64) bool
IsNaN(f float64) (is bool)
J0(x float64) float64
J1(x float64) float64
Jn(n int64, x float64) float64
Ldexp(frac float64, exp int64) float64
MathLog(x float64) float64
Log10(x float64) float64
Log1p(x float64) float64
Log2(x float64) float64
Logb(x float64) float64
Mod(x, y float64) float64
NaN() float64
Pow(x, y float64) float64
Pow10(n int64) float64
Remainder(x, y float64) float64
Round(x float64) float64
RoundToEven(x float64) float64
Signbit(x float64) bool
Sin(x float64) float64
Sinh(x float64) float64
Sqrt(x float64) float64
Tan(x float64) float64
Tanh(x float64) float64
Trunc(x float64) float64

Constant Functions

The following functions can be called from within GRL as long as the receiver value type is correct.

string.Len() int

Len will return string's length.

Returns

The length of string's receiver

Example

rule DoSomething "Do something when string length is sufficient" {
    when
        Fact.Name.Len() > "ATextConstant".Len()
    then
        Fact.DoSomething();
}

string.Compare(string) int

Compare will compare the receiver string to the argument.

Arguments

string The string to compare to

Returns

< 0 if receiver is less than the argument
0 if receiver is equal to the argument
> 0 if receiver is greater thant the argument

Example

rule CompareString "Do something when Fact.Text is greater than A" {
    when
        Fact.Text.Compare("A") > 0
    then
        Fact.DoSomething();
}

string.Contains(string) bool

Contains will check if its argument is contained within the receiver.

Arguments

string The substring to check within the receiver

Returns

true if the argument string is contained within the receiver.
false if the argument string is not contained within the receiver.

Example

rule ContainString "Do something when Fact.Text is contains XXX" {
    when
        Fact.Text.Contains("XXX")
    then
        Fact.DoSomething();
}

string.In(string ...) bool

In will check if the any of the argument is equals to the receiver.

Arguments

string The variadic string argument to check

Returns

bolean true if any of the argument is equals to the receiver, or false if otherwise.

Example

rule CheckArgumentIn "Do something when Fact.Text is equals to 'ABC' or 'BCD' or 'CDE' " {
    when
        Fact.Text.In("ABC", "BCD", "CDE")
    then
        Fact.DoSomething();
}

string.Count(string) int

Count will count the number of occurences of argument in receiver string.

Arguments

string The substring to count within the receiver

Returns

number of occurences of the argument in the receiver.

Example

rule CountString "Do something when Fact.Text contains 3 occurrences of 'ABC'" {
    when
        Fact.Text.Count("ABC") == 3
    then
        Fact.DoSomething();
}

string.HasPrefix(string) bool

HasPrefix will check if the receiver string has a specific prefix.

Arguments

string The expected prefix.

Returns

true if the receiver has the argument as its prefix.
false if the receiver does not have the argument as its prefix.

Example

rule IsPrefixed "Do something when Fact.Text started with PREF" {
    when
        Fact.Text.HasPrefix("PREF")
    then
        Fact.DoSomething();
}

string.HasSuffix(string) bool

HasSuffix will check if the receiver string has a specific suffix.

Arguments

string The expected suffix.

Returns

true if the receiver has the argument as its suffix.
false if the receiver does not have the argument as its suffix.

Example

rule IsSuffixed "Do something when Fact.Text ends with SUFF" {
    when
        Fact.Text.HasSuffix("SUFF")
    then
        Fact.DoSomething();
}

string.Index(string) int

Index will return the index of the first occurrence of the argument in the receiver string.

Arguments

string The substring to search for.

Returns

The index value of the first occurrence of the argument.

Example

rule IndexCheck "Do something when Fact.Text ABC occurs as specified" {
    when
        Fact.Text.Index("ABC") == "abABCabABC".Index("ABC")
    then
        Fact.DoSomething();
}

string.LastIndex(string) int

LastIndex will return the index of last occurrence of the argument in the receiver string.

Arguments

string The substring to search for.

Returns

The index of the last occurrence of the argument.

Example

rule LastIndexCheck "Do something when Fact.Text ABC occurs in the last position as specified" {
    when
        Fact.Text.LastIndex("ABC") == "abABCabABC".LastIndex("ABC")
    then
        Fact.DoSomething();
}

string.Repeat(int64) string

Repeat will return a string containing n occurrences of the receiver string.

Arguments

int64 the repeat count

Returns

A new string containing n occurrences of the receiver.

Example

rule StringRepeat "Do something when Fact.Text contains ABCABCABC" {
    when
        Fact.Text == "ABC".Repeat(3)
    then
        Fact.DoSomething();
}

string.Replace(old, new string) string

Replace will return a string with all occurrences of old replaced with new.

Arguments

old the substring you wish to have replaced.
new the string you wish to replace all occurrences of old.

Returns

A string where all instances of old in the receiver have been replaced with new.

Example

rule ReplaceString "Do something when Fact.Text contains replaced string" {
    when
        Fact.Text == "ABC123ABC".Replace("123","ABC")
    then
        Fact.DoSomething();
}

string.Split(string) []string

Split will return a string slice whose elements are determined after splitting the receiver by the string token argument. The token will not be present in the resulting slice elements.

Arguments

string the token you wish to use to split the receiver.

Returns

The string slice containing parts of the original string as split by the token.

Example

rule SplitString "Do something when Fact.Text is prefixed by 'ABC,'" {
    when
        Fact.Text.Split(",")[0] == "ABC"
    then
        Fact.DoSomething();
}

string.ToLower() string

ToLower will return a string whose contents are all lower case instances of characters in the receiver.

Returns

A new string that is a lower-cased version of the receiver.

Example

rule LowerText "Do something when Fact.Text is equal to 'abc'" {
    when
        Fact.Text.ToLower() == "Abc".ToLower()
    then
        Fact.DoSomething();
}

string.ToUpper() string

ToUpper will return a string whose contents are all upper case instances of characters in the receiver.

Returns

A new string that is an upper-cased version of the receiver.

Example

rule UpperText "Do something when Fact.Text is equal to 'ABC'" {
    when
        Fact.Text.ToUpper() == "Abc".ToUpper()
    then
        Fact.DoSomething();
}

string.Trim() string

Trim will return a string where the whitespace on either end of the string has been removed.

Returns

A string with the whitespace removed from the beginning and end.

Example

rule TrimText "Do something when Fact.Text is 'ABC'" {
    when
        Fact.Text == "  Abc   ".Trim().ToUpper()
    then
        Fact.DoSomething();
}

string.MatchString() string

MatchString MatchString reports whether the string s contains any match of the regular expression pattern. Similar to golang MatchString

Returns

True if the regexPattern matches the string s
False if the regexPattern doesn't match the string s

Example

rule MatchStringText "Return true when regex pattern matches the string"  {
	when
	  Fact.Text.MatchString("B([a-z]+)ck")
	then
	  Fact.DoSomething();
}

array.Len() int

Len will return the length of the array/slice.

Returns

The length of array/slice.

Example

rule DoSomething "Do something when array length is sufficient" {
    when
        Fact.ChildrenArray.Len() > 2
    then
        Fact.DoSomething();
}

array.Append(val)

Append will append val onto the end of the receiver array.

Arguments

val value to have appended.

Example

rule DoSomething "Add a new child when the array has less than 2 children" {
    when
        Fact.ChildrenArray.Len() < 2
    then
        Fact.ChildrenArray.Append(Fact.NewChild());
}

map.Len() int

Len will return map's length.

Returns

The length of map receiver.

Example

rule DoSomething "Do something when map length is sufficient" {
   when
       Fact.ChildrenMap.Len() > 2
   then
       Fact.DoSomething();
}

Custom Functions

All functions that are acessible from the DataContext are Invocable from within the rule, both in the "When" scope and the "Then" scope.

You can create functions and have your Fact as receiver, and those functions can be called from GRL.

For example. Given:

type MyPoGo struct {
}

func (p *MyPoGo) GetStringLength(sarg string) int {
    return len(sarg)
}

func (p *MyPoGo) AppendString(aString, subString string) string {
    return sprintf("%s%s", aString, subString)
}

You can make calls to the defined methods:

dctx := grule.context.NewDataContext()
dctx.Add("Pogo", &MyPoGo{})

rule "If it's possible to Groool, Groool" {
    when
        Pogo.GetStringLength(some.variable) < 100
    then
        some.variable = Pogo.AppendString(some.variable, "Groooling");
}

Variadic Function Arguments

Variadic arguments are supported for custom functions.

func (p *MyPoGo) GetLongestString(strs... string) string {
    var longestStr string
    for _, s := range strs {
        if len(s) > len(longestStr) {
            longestStr = s
        }
    }
    return longestStr
}

This function can then be called from within a rule with zero or more values supplied for the variadic argument.

when
    Pogo.GetStringLength(some.variable) < 100
then
    some.longest = Pogo.GetLongestString(some.stringA, some.stringB, some.stringC);

Since it is possible to provide zero values to satisfy a variadic argument, they can also be used to simulate optional parameters.

func (p *MyPoGo) AddTax(cost int64, optionalTaxRate... float64) int64 {
    var taxRate float64 = 0.2
    if len(optionalTaxRate) > 0 {
        taxRate = optionalTaxRate[0]
    }
    return cost * (1+taxRate)
}

when
    Pogo.IsTaxApplied() == false
then
    some.cost = Pogo.AddTax(come.cost);

//or

when
    Pogo.IsTaxApplied() == false
then
    some.cost = Pogo.AddTax(come.cost, 0.15);

The Laws of Custom Function in Grule

When you make your own function to be called from the rule engine, you need to know the following laws:

The function must be visible, meaning that functions must start with a capital letter. Private functions cannot be executed.
The function must only return one value type. Returning multiple values from a function is not supported and the rule execution will fail if there are multiple return values.
The way number literals are treated in Grule's GRL is such that a integer will always be taken as an int64 type and a real as float64, thus you must always define your numeric types accordingly.

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Function in Grule

Built-In Functions

MakeTime(year, month, day, hour, minute, second int64) time.Time

Arguments

Returns

Example

Changed(variableName string)

Arguments

Example

Now() time.Time

Returns

Example

Log(text string)

Arguments

Example

IsNil(i interface{}) bool

Arguments

Returns

Example

IsZero(i interface{}) bool

Arguments

Returns

Example

Retract(ruleName string)

Arguments

Example

GetTimeYear(time time.Time) int

Arguments

Returns

Example

GetTimeMonth(time time.Time) int

Arguments

Returns

Example

GetTimeDay(time time.Time) int

Arguments

Returns

Example

GetTimeHour(time time.Time) int

Arguments

Returns

Example

GetTimeMinute(time time.Time) int

Arguments

Returns

Example

GetTimeSecond(time time.Time) int

Arguments

Returns

Example

IsTimeBefore(time, before time.Time) bool

Arguments

Returns

Example

IsTimeAfter(time, after time.Time) bool

Arguments

Returns

Example

TimeFormat(time time.Time, layout string) string

Arguments

Returns

Example

Complete()

Example

Math Functions

Constant Functions

string.Len() int

Returns

Example

string.Compare(string) int

Arguments

Returns

Example

string.Contains(string) bool