# unicode.ludic — Unicode.* correctness over UTF-8. Byte counting is wrong for
# non-ASCII, so we assert the code-point / grapheme invariants that must hold:
# len counts code points not bytes, validation accepts good UTF-8, char access
# never splits a character, case mapping round-trips, truncate keeps whole
# characters, and grapheme_len collapses combining marks, ZWJ emoji, and flags.
# Running it prints: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
program Unicode {
  entry {
    # code points vs bytes
    if Unicode.len("héllo") == 5 { print(1) }
    if Unicode.byte_len("héllo") == 6 { print(2) }
    if Unicode.len("abc") == 3 { print(3) }

    # validation of well-formed UTF-8
    if Unicode.is_valid_utf8("héllo") { print(4) }

    # code-point access by index (é is U+00E9 = 233), out of range -> -1
    if Unicode.char_at("héllo", 0) == 104 { print(5) }
    if Unicode.char_at("héllo", 1) == 233 { print(6) }
    if Unicode.char_at("héllo", 5) < 0 { print(7) }

    # chars() yields every code point in order
    let cs = Unicode.chars("héllo")
    if len(cs) == 5 { print(8) }
    if cs[1] == 233 { print(9) }

    # case mapping (ASCII + Latin-1) round-trips
    if Unicode.upper("héllo") == "HÉLLO" { print(10) }
    if Unicode.lower("HÉLLO") == "héllo" { print(11) }

    # truncate keeps whole characters: first 3 code points of "héllo" is "hél"
    if Unicode.truncate("héllo", 3) == "hél" { print(12) }

    # grapheme clustering: ASCII is one grapheme per code point
    if Unicode.grapheme_len("abc") == 3 { print(13) }

    # a combining accent joins its base: "café" decomposed is 5 code points but
    # 4 user-perceived characters
    if Unicode.grapheme_len("café") == 4 { print(14) }
    if Unicode.len("café") == 5 { print(15) }

    # a ZWJ emoji sequence (family) is 5 code points but one grapheme
    if Unicode.grapheme_len("👨‍👩‍👧") == 1 { print(16) }
    if Unicode.len("👨‍👩‍👧") == 5 { print(17) }

    # a flag is two regional indicators but one grapheme
    if Unicode.grapheme_len("🇺🇸") == 1 { print(18) }
  }
}