Result

Result .T .E は「成功値 / 失敗理由」を型で表します。失敗しうる関数は Result を返し、呼び出し側が match で成功と失敗を分けます。

TESTstdionormalize_newlines

#entry main
#indent 4
#target std

#import "core/result" as *
#import "std/test" as *
#import "core/math" as *

fn divide_10 %fn i32 Result i32 str \x:
    if:
        eq x 0
        then:
            Result::Err "division by zero"
        else:
            Result::Ok div_s 10 x

fn expect_ok %fn Result i32 str fn i32 Result unit str \got\expected:
    match got:
        Result::Ok value:
            check_eq_i32 expected value
        Result::Err msg:
            Result::Err msg

fn expect_err %fn Result i32 str fn str Result unit str \got\expected:
    match got:
        Result::Ok value:
            Result::Err "expected Err"
        Result::Err msg:
            check_str_eq expected msg

fn main %impure fn void i32 \void:
    let checks:
        checks_new
        |> checks_push expect_ok divide_10 2 5
        |> checks_push expect_err divide_10 0 "division by zero"
    let shown checks_print_report checks
    checks_exit_code shown

Result の中身を取り出す関数を小さく分けると、正常系と異常系の扱いをテストしやすくなります。