Perhaps I'm just having a bout of Perl envy, but I keep wanting to implement an ''lmap'' and ''lgrep'' set of procs that do map and grep on lists.  Sample usage:

  % set l [list a b c d]
  a b c d

  % lmap l { format %s%s $_ $_ }
  aa bb cc dd

  % lgrep l { string match *d* $_ }
  d

These are easy enough to implement in Tcl:

  proc lmap {listName expr} {
    upvar $listName list
    foreach _ $list {
      lappend newList [eval $expr]
    }
    return $newList
  }

  proc lgrep {listName expr} {
    upvar $listName list
    foreach _ $list {
      if [eval $expr] {
        lappend newList $_
      }
    }
    return $newList
  }

Does anyone else wish these were part of standard Tcl?  Would someone want to write up the TIP to try and get this in?

-- [Dossy] 13aug2003
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[RS] What you want (and have implemented) are the classic ''map'' ([function mapping]) and ''filter'' functions. The term ''lgrep'' seems not so good to me, as ''grep'' is etymologized as "general regular expression parser", and ''filter'' allows much more than that.

However, use of an implicit variable _ is no good Tcl style. I'm afraid one would have to call these with named or anonymous functions ([Lambda in Tcl]):
 lmap2   [lambda x {format %s%s $x $x}]   $list    ;# pass values, not names!
 lfilter [lambda x {string match *d* $x}] $list
And I think, as easily these are implemented, there's no need to TIP a core change...
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