This Commented CUE demonstrates constraining the sum of a list of numbers.
schema.cue
package example
import "list"
// both data fields are lists of numbers
good_list: [...number]
bad_list: [...number]
// We introduce a hidden CUE field for each list
// we want to check. Each hidden field unifies
// the relevant value constraint with the list's
// sum
_good_sum: <=100 & list.Sum(good_list)
_bad_sum: <=99.5 & list.Sum(bad_list)data.yml
good_list: [ 1,2,3,4 ]
bad_list: [ 1,2,3,100.5 ]TERMINAL
$ cue vet .:example data.yml
_bad_sum: invalid value 106.5 (out of bound <=99.5):
./schema.cue:14:12
./schema.cue:14:21