factorial_question_answer_sequence.puml

@startuml
/' computes the factorial of the given integer. '/
!function $factorial($n)
    /' Return value of this function is memoized because it uses recursion. 
    PlantUML preprocessor doesn't provide dictionary or array data structure, 
    hence a "hack" simulates a dictionary. For every input integer, a variable 
    is created with the stringized integer as its name, and the return value is 
    assigned to it. Thus, the variable's name serves as the "key". '/
    !if %variable_exists(%string($n))
        !return %get_variable_value(%string($n))
    !endif

    !if $n == 0
        !$value = 1
    !else
        !$value = $n * $factorial($n - 1)
    !endif

    %set_variable_value(%string($n), $value)
    !return $value
!endfunction

!procedure $factorial_question_answer_sequence(\
        $starting_number = 0,\
        $ending_number = 12,\
        $color_number_in_question = blue,\
        $color_number_in_answer = green)
    skinparam SequenceMessageAlignment direction
    !$number = $starting_number
    !while $number <= $ending_number
        Question -> Answer : What is factorial of <color:$color_number_in_question>**$number**</color>?
        Question <- Answer : Factorial of <color:$color_number_in_question>**$number**</color> is <color:$color_number_in_answer>**$factorial($number)**</color>.
        |||
        !$number = $number + 1
    !endwhile
!endprocedure

scale 1.5 /' zooms the generated diagram per specified scaling factor '/
$factorial_question_answer_sequence(\
    $color_number_in_answer = darkviolet, $color_number_in_question = red\
)
@enduml