LengthVariation

extends: script
message: "This paragraph has a stdev less than 2"
link: https://tengolang.com/
scope: paragraph
script: |
  text := import("text")
  math := import("math")

  matches := []

  each := func(seq, fn) {
    for x in seq {
        fn(x)
    }
  }

  sum := func(seq) {
    s := 0
    each(seq, func(x) {
      s += x
    })
    return s
  }

  stdev := func(seq) {
    size := len(seq)
    mean := sum(seq) / size

    sd := 0.0
    each(seq, func(x) {
      sd += math.pow(x - mean, 2)
    })

    return math.sqrt(sd / size)
  }

  lengths := []
  for sent in text.re_split(`[.!?] `, scope, -1) {
    lengths = append(lengths, len(text.fields(sent)))
  }

  computed := stdev(lengths)
  if computed < 2 && len(lengths) >= 3 {
    matches = append(matches, {begin: 0, end: len(scope)})
  }