While for loops are not supported in custom functions, you can use Range to implement loop logic.

Definition:

Range range = Ranges.of(Integer start,Integer end)

range.each{

}

Note: Maximum 500 iterations allowed.

Example:

Range range = Ranges.of(1,5)

range.each{ it ->
  log.info(it)
}  
//[1,2,3,4,5]