value by ranges

displayValue() is the function you need. 
docs.appian.com/.../fnc_conversion_displayvalue.html

Assuming that the list of ranges is sorted, the following code should do this. I use the list comprehension feature of operators to compare x to all ranges, the use where() to get the indexes of matches, pick the first match and the pick the value for that matching index.

a!localVariables(
  local!x: 4,
  local!values: {23, 5, 468, 123, 42, 500},
  local!ranges: {1, 2, 3, 4, 5},
  index(
    local!values,
    index(where(local!x <= local!ranges), 1, count(local!values)),
    0
  )
)