Unexpected handling of "variables" in cmd.exe batch file

I have a xyz.bat file with this content:

@set val=one
@if "%val%" equ "one" (
   @set val=yes
   echo val after setting it: %val%
) else (
   @set val=no
)
@echo %val%

Running it in cmd.exe prints

val after setting it: one
yes

but I expected

val after开发者_JAVA百科 setting it: yes
yes

Why is this? And is there a way to make it behave as I think it should?

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Everything between ( and ) is parsed as a single line (joining commands with &) – and the shell expands %var% variables at parse time

The output of set /? explains this further.

In recent versions:

@echo off
setlocal enabledelayedexpansion
set var=one
if a equ a (
    set var=two
    echo immediate expansion: %var%
    echo delayed expansion:   !var!
)
echo after: %var%

• The Old New Thing: Environment variable expansion occurs when the command is read

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...but that way lies madness. For example, if you want to echo a ! in delayed expansion mode, you have to escape it twice:

echo hi^^!

(This gets parsed twice, reduced to echo hi^! the first time.) And don't even get me started on using ^ inside variables.

• The Old New Thing: What this batch file needs is more escape characters

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Consider a less kludgy language (Perl, Python, PowerShell, PHP, JScript, C#, ...)