ifelse.kts

// top level function
inline fun ifp(boolean: Boolean?, noinline statements: ()->Unit) 
         = NonReturningIfContinuation().ElseIfP(boolean, statements)
inline fun ifn(boolean: Boolean?, noinline statements: ()->Unit) 
         = NonReturningIfContinuation().ElseIfN(boolean,statements)
inline fun <reified T> retIfn(boolean: Boolean?, noinline statements: ()->T) 
         = ReturningIfContinuation<T>().ElseIfN(boolean,statements)
inline fun <reified T> retIfP(boolean: Boolean?, noinline statements: ()->T) 
         = ReturningIfContinuation<T>().ElseIfN(boolean,statements)

/**
* class for if-statement, which don't return anyhing.
* This is to not have to wory about the returtypes of the statements
*/
class NonReturningIfContinuation{
    var caseReached: Boolean = false
    //--------------- pass booleans directly to the function
    fun ElseIf(condition: Boolean, statements: ()->Unit) = this.apply {
        if (!caseReached && condition) {
            statements()
            caseReached = true
        }
    }
    fun ElseIfP(condition: Boolean?, statements: ()->Unit) 
            = ElseIf(condition==true, statements)
    fun ElseIfN(condition: Boolean?, statements: () -> Unit) 
            = ElseIf(condition==false, statements)

    //---------------------------- pass booleans lazy
    fun ElseIf(getBoolean: ()->Boolean, statements: () -> Unit) = this.apply {
        if (!caseReached && getBoolean()) {
            statements()
            caseReached = true
        }
    }
    fun ElseIfP(getBoolean: () -> Boolean?, statements: () -> Unit) 
            = ElseIf({getBoolean() == true}, statements)
    fun ElseIfN(getBoolean: () -> Boolean?, statements: () -> Unit) 
            = ElseIf({getBoolean() == false}, statements)

    //----------------------------get value
    infix fun Else(statements: () -> Unit) { if (caseReached) statements() }
    fun endIf() {} //not necesary, but used for matching ReturningIfContinuation
}

/**
* Class for if with returnvalue
* To be safe, this class makes no usage of casts.
* This meansthe returntype matches the type being inferred, or stated at the returntype 
*/
class ReturningIfContinuation<T>(var retValue: T? = null){
    var caseReached: Boolean = false
//----------------------------- pass boolean directly -------
    fun ElseIf(boolean: Boolean, statements: ()->T) = this.apply {
        if (!caseReached && boolean) {
            retValue = statements()
            caseReached = true
        }
    }

    fun ElseIfP(boolean: Boolean?, statements: ()->T) 
             = ElseIf(boolean==true, statements)
    fun ElseIfN(boolean: Boolean?, statements: () -> T) 
             = ElseIf(boolean==false, statements)

    //--------------------------- pass booleans lazy ------------------
    fun ElseIf(getBoolean: ()->Boolean, statements: () -> T) = this.apply { 
        if (!caseReached && getBoolean()){
            retValue = statements()
            caseReached = true
        }
    }
    
    fun ElseIfP(getBoolean: ()->Boolean?, statements: () -> T)
         = ElseIf({getBoolean() == true}, statements)
    fun ElseIfN(getBoolean: ()->Boolean?, statements: () -> T) 
        = ElseIf({getBoolean() == false}, statements)

    //--------------------- finishing------------------------
    infix fun Else(statements: () -> T) = if (caseReached) retValue else statements()
    fun endIf() : T? = if (caseReached) retValue else null
}