165 lines
4.1 KiB
Plaintext
165 lines
4.1 KiB
Plaintext
# Copyright 2017-2018 Free Software Foundation, Inc.
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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# This file implements some simple data structures in Tcl.
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# A namespace/commands to support a stack.
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#
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# To create a stack, call ::Stack::new, recording the returned object ID
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# for future calls to manipulate the stack object.
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#
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# Example:
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#
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# set sid [::Stack::new]
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# stack push $sid a
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# stack push $sid b
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# stack empty $sid; # returns false
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# stack pop $sid; # returns "b"
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# stack pop $sid; # returns "a"
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# stack pop $sid; # errors with "stack is empty"
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# stack delete $sid1
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namespace eval ::Stack {
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# A counter used to create object IDs
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variable num_ 0
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# An array holding all object lists, indexed by object ID.
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variable data_
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# Create a new stack object, returning its object ID.
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proc new {} {
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variable num_
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variable data_
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set oid [incr num_]
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set data_($oid) [list]
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return $oid
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}
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# Delete the given stack ID.
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proc delete {oid} {
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variable data_
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error_if $oid
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unset data_($oid)
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}
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# Returns whether the given stack is empty.
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proc empty {oid} {
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variable data_
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error_if $oid
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return [expr {[llength $data_($oid)] == 0}]
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}
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# Push ELEM onto the stack given by OID.
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proc push {oid elem} {
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variable data_
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error_if $oid
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lappend data_($oid) $elem
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}
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# Return and pop the top element on OID. It is an error to pop
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# an empty stack.
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proc pop {oid} {
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variable data_
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error_if $oid
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if {[llength $data_($oid)] == 0} {
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::error "stack is empty"
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}
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set elem [lindex $data_($oid) end]
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set data_($oid) [lreplace $data_($oid) end end]
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return $elem
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}
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# Returns the depth of a given ID.
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proc length {oid} {
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variable data_
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error_if $oid
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return [llength $data_($oid)]
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}
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# Error handler for invalid object IDs.
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proc error_if {oid} {
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variable data_
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if {![info exists data_($oid)]} {
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::error "object ID $oid does not exist"
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}
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}
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# Export procs to be used.
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namespace export empty push pop new delete length error_if
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# Create an ensemble command to use instead of requiring users
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# to type namespace proc names.
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namespace ensemble create -command ::stack
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}
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# A namespace/commands to support a queue.
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#
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# To create a queue, call ::Queue::new, recording the returned queue ID
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# for future calls to manipulate the queue object.
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#
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# Example:
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#
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# set qid [::Queue::new]
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# queue push $qid a
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# queue push $qid b
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# queue empty $qid; # returns false
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# queue pop $qid; # returns "a"
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# queue pop $qid; # returns "b"
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# queue pop $qid; # errors with "queue is empty"
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# queue delete $qid
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namespace eval ::Queue {
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# Remove and return the oldest element in the queue given by OID.
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# It is an error to pop an empty queue.
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proc pop {oid} {
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variable ::Stack::data_
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error_if $oid
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if {[llength $data_($oid)] == 0} {
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error "queue is empty"
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}
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set elem [lindex $data_($oid) 0]
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set data_($oid) [lreplace $data_($oid) 0 0]
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return $elem
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}
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# "Unpush" ELEM back to the head of the queue given by QID.
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proc unpush {oid elem} {
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variable ::Stack::data_
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error_if $oid
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set data_($oid) [linsert $data_($oid) 0 $elem]
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}
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# Re-use some common routines from the Stack implementation.
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namespace import ::Stack::create ::Stack::new ::Stack::empty \
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::Stack::delete ::Stack::push ::Stack::length ::Stack::error_if
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# Export procs to be used.
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namespace export new empty push pop new delete length error_if unpush
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# Create an ensemble command to use instead of requiring users
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# to type namespace proc names.
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namespace ensemble create -command ::queue
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}
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