In order to do explorative programming in Tcl shell using macports extensions a self contained script is provided here, the script merges ​script.tcl from tcl.tk wiki and instructions from committers' tips and tricks.

The script also uses rlwrap and tcl from macports itself, save it with a name like mpsh somewhere in your path, for instance $prefix/bin, and make it executable.

#!/usr/bin/env rlwrap port-tclsh

namespace eval prompt {}

proc prompt::_init {} {
    variable buffer ""
    variable continue 0
    variable prompt1 "% "
    variable prompt2 ""
    return
}

proc prompt::_getline {line} {    
    variable buffer
    variable continue   
    set n1 [string length $line]
    set line2 [string trimright $line \\]
    set n2 [string length $line2]
    set cont [expr {($n1 - $n2) % 2 == 1}]
    if { $cont } {
      set line [string range $line 0 end-1]
    }
    if { $continue } {
      append buffer " [string trimleft $line]"
    } elseif { [string length $buffer] } {
      append buffer \n$line
    } else {
      set buffer $line
    }
    set continue $cont
    if { $continue } {
      set complete 0
    } else {
      set complete [info complete $buffer]
    }
    if { !$continue && [info complete $buffer] } {
      set code [catch {uplevel #0 $buffer} result]
      set std [expr {$code > 0 ? "stderr" : "stdout"}]
      if { [string length $result] } {
        puts $std "$result"
      }
      set buffer ""
      _prompt 1
    } else {
      _prompt 2
    }    
    return
}

proc prompt::_readable {chan} {    
    variable status
    set code [catch {gets $chan line} chars]    
    if { $code > 0 } {
      puts stderr "error reading $chan: $chars"
      set status "error"
    } elseif { $chars > -1 } {
      _getline $line
    } elseif { [eof $chan] } {
      set status "eof"
    } elseif { [fblocked $chan] } {
      return
    } else {
      set status "unknown"
    }    
    return
}

proc prompt::_prompt {n} {
    global tcl_prompt$n
    variable prompt$n
    if { [info exists tcl_prompt$n] } {
      if { [catch {uplevel #0 [set tcl_prompt$n]} result] } {
        puts stderr $result
        flush stderr
      }
    } else {
      puts -nonewline stdout [set prompt$n]
    }
    flush stdout
    return
}

proc prompt::prompt {} {
    _prompt 1
    fileevent stdin readable [list [namespace current]::_readable stdin]
    vwait [namespace current]::status
    return
}

package require macports
mportinit
package require Pextlib

prompt::_init
if { [info exists argv0] && [string equal $argv0 [info script]] } {
    #   set tcl_prompt2 {puts -nonewline "> "}
      set prompt::prompt2 "> "
      prompt::prompt
}