Number to words — spell out integers 0..999

number_to_words.cell

// ============================================================================
// Number to words — spell out integers 0..999
// ============================================================================
//
// Composes English number words from ones/teens/tens tables. Demonstrates
// list-literal lookup tables indexed by digit, integer division with floor,
// and string assembly with trim to drop stray spaces.
//
// Run: soma run number_to_words.cell --signal spell 342

cell NumberToWords {
    face {
        signal spell(n: Int) -> String
    }

    on _ones(d: Int) {
        let t = list("zero","one","two","three","four","five","six","seven","eight","nine")
        return t[d]
    }

    on _teens(d: Int) {
        let t = list("ten","eleven","twelve","thirteen","fourteen","fifteen","sixteen","seventeen","eighteen","nineteen")
        return t[d]
    }

    on _tens(d: Int) {
        let t = list("","","twenty","thirty","forty","fifty","sixty","seventy","eighty","ninety")
        return t[d]
    }

    // Spell 0..99
    on _two_digits(n: Int) {
        if n < 10 { return _ones(n) }
        if n < 20 { return _teens(n - 10) }
        let tens = floor(n / 10)
        let ones = n % 10
        if ones == 0 { return _tens(tens) }
        return _tens(tens) + "-" + _ones(ones)
    }

    on spell(n: Int) {
        if n == 0 { return "zero" }
        if n < 100 { return _two_digits(n) }
        let hundreds = floor(n / 100)
        let rest = n % 100
        let out = _ones(hundreds) + " hundred"
        if rest > 0 {
            out = out + " " + _two_digits(rest)
        }
        return out
    }
}

cell test NumberToWordsTest {
    rules {
        assert spell(0) == "zero"
        assert spell(7) == "seven"
        assert spell(13) == "thirteen"
        assert spell(20) == "twenty"
        assert spell(42) == "forty-two"
        assert spell(100) == "one hundred"
        assert spell(342) == "three hundred forty-two"
        assert spell(905) == "nine hundred five"
    }
}