char と ASCII

char は Unicode scalar value です。ASCII 判定や UTF-8 encode の補助は core/char にあります。str の byte index と char の値は分けて考えます。

TESTstdionormalize_newlines

#entry main
#indent 4
#target std

#import "alloc/string" as *
#import "core/char" as *
#import "core/result" as *
#import "std/test" as *

fn expect_char %fn Result char str fn i32 Result unit str \got\expected_code:
    match got:
        Result::Ok c:
            check_eq_i32 expected_code char_to_i32 c
        Result::Err msg:
            Result::Err msg

fn main %impure fn void i32 \void:
    let a %char 'A'
    let hira %char 'あ'
    let checks:
        checks_new
        |> checks_push assert_eq_i32 65 char_to_i32 a
        |> checks_push assert char_is_ascii_alpha a
        |> checks_push assert char_is_ascii_digit '7'
        |> checks_push assert char_is_ascii_whitespace '\n'
        |> checks_push assert_eq_i32 1 char_utf8_len a
        |> checks_push assert_eq_i32 3 char_utf8_len hira
        |> checks_push expect_char str_char_at_result "Aあ" 1 0x3042
    let shown checks_print_report checks
    checks_exit_code shown

ASCII だけを受け付ける処理では char_is_ascii_* を使います。任意の text を 1 byte として扱うのは誤りです。