#!/usr/bin/env wish -f
proc power {base p} {
  set result 1
  while {$p > 0} {
    set result [expr $result*$base]
    set p [expr $p-1]
  }
  return $result
}

#set result 0
entry .base -width 6 -relief sunken -textvariable base
label .label1 -text "to the power"
entry .power -width 6 -relief sunken -textvariable power
label .label2 -text "is"
label .result -textvariable result
pack .base .label1 .power .label2 .result -side left \
  -padx 1m -pady 2m
bind .base <Return> {set result [power $base $power]; puts $result}
bind .power <Return> {set result [power $base $power]}