iu2 2009-03-24 This is a calculator application. So, What's the big deal? The way the window's caption is used...
I apologize, this is very silly, but at the same time a bit challenging, I think. I don't think this could be more elegant in other languages (of the few I know...) thanks to after, trace and binding
Here it is:
package require Tk
label .lbl -text "Type a calculation in this odd calculator and press ENTER.\nType 'exit' to exit"
pack .lbl
set ::exp ""
set ::caret _
bind . <Key> {
if {[string is print "%A"]} {
append ::exp %A
} elseif {"%K" eq "BackSpace"} {
set ::exp [string range $::exp 0 end-1]
} elseif {%k == 13} calc
}
proc calc {} {
if {![catch {expr $::exp} res]} {
set ::exp $res
} elseif {$::exp eq "exit"} {
set ::exp Bye...
after 1000 {destroy .}
}
}
proc blink {} {
if {$::caret eq "_"} {set ::caret ""} {set ::caret "_"}
wm title . $::exp$::caret
after 250 blink
}
trace add variable ::exp write {apply {{name1 name2 op} {wm title . $::exp}}}
raise .
after 250 blink
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