!! +exec+ +var+ +string+
$lst_tit evalsubst$lst_titend$type_both
  $lst_alias evalsubstit, evalsubstitute, evaluesubst,
    evaluesubstit, evaluesubstitute
  $(lst_syntax)evalsubst $emph name=val $emphend in $emph
  expr$emphend</tt>
  $lst_mean 对数学表达式的操作: 把表达式 $emph expr$emphend 
  里的变量 $emph name$emphend 替换成 $emph val$emphend,
  然后计算表达式的实数值. <br/>
  在 $emph name$emphend 内不允许正则表达式. <br/>
  请参看命令
  $(ref1)cmdlist_mathsubst_&cmd_choose=all$(ref2)cmdlist_mathsubst_">!mathsubst</a>,
  $(ref1)cmdlist_replace_&cmd_choose=all$(ref2)cmdlist_replace_">!replace</a>.



