Stack: Difference between revisions

=={{header|Tcl}}==

Here's a simple implementation using a list:

<lang tcl>proc push {stackvar value} {

upvar 1 $stackvar stack

lappend stack $value

}

proc pop {stackvar} {

upvar 1 $stackvar stack

set value [lindex $stack end]

set stack [lrange $stack 0 end-1]

return $value

}

proc size {stackvar} {

upvar 1 $stackvar stack

llength $stack

}

proc empty {stackvar} {

upvar 1 $stackvar stack

expr {[size stack] == 0}

}

proc peek {stackvar} {

upvar 1 $stackvar stack

lindex $stack end

}

set S [list]

empty S ;# ==> 1 (true)

push S foo

empty S ;# ==> 0 (false)

push S bar

peek S ;# ==> bar

pop S ;# ==> bar

peek S ;# ==> foo</lang>

There is a package in [http://tcllib.sourceforge.net/ tcllib] called <code>struct::stack</code> that presents an object interface:

<lang tcl>package require struct::stack

struct::stack S

S size ;# ==> 0

S push a b c d e

S size ;# ==> 5

S peek ;# ==> e

S pop ;# ==> e

S peek ;# ==> d

S pop 4 ;# ==> d c b a

S size ;# ==> 0</lang>