test2.tcl

proc is_admin {
  user_id
} {
  switch $user_id {
    1 -
    3 -
    5 { return true }
    default { return false }
  }
}

rename if if_old

proc if {
  condition
  block
} {
  if_old {$condition == {[is_admin $user_id]}} {
    upvar user_id user_id
    if_old {$user_id == 22157} {
      uplevel 1 $block
    }
  } else {
    set result [uplevel 1 expr $condition]
    if_old {$result} {
      uplevel 1 $block
    }
  }
}

set user_id 22157

if {[is_admin $user_id]} {
  puts "$user_id is an admin and can do admin things"
}