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# generator.tcl --
#
# Iterators and generators via coroutines.
#
# Copyright (c) 2009 by Neil Madden <nem@cs.nott.ac.uk>
#
# See the file "license.terms" for information on Usage and redistribution
# of this file, and for a DISCLAIMER OF ALL WARRANTIES.
#
# RCS: @(#) $Id: generator.tcl,v 1.1 2012/08/08 23:23:06 andreas_kupries Exp $
#
package require Tcl 8.6
package provide generator 0.1
namespace eval generator {
namespace export {[a-z]*}
namespace ensemble create
# next generator varName ?varName ..? --
#
# Fetch the next values from a generator, assigning them to variables. If
# the generator is exhausted any remaining variables are assigned the
# empty string.
#
proc next {generator args} {
set items [takeList [llength $args] $generator]
uplevel 1 [list lassign $items {*}$args]
}
proc takeList {n generator} {
if {![exists $generator]} { return [list] }
set ret [list]
for {set i 0} {$i < $n} {incr i} {
set item [$generator]
if {[llength $item] == 0} { break }
lappend ret [lindex $item 0]
}
return $ret
}
# foreach varSpec generator ?varSpec generator ...? body --
#
# Iterate over the elements of one or more generator functions. Each
# generator is a command that yields successive elements. The syntax
# of this construct closely matches that of the built-in foreach
# command.
#
proc foreach args {
if {[llength $args] < 3 || ([llength $args] % 2) != 1} {
Usage "foreach varSpec generator ?varSpec generator ..? body"
}
set body [lindex $args end]
set genSpec [lrange $args 0 end-1]
set items [list]
::foreach {varList generator} $genSpec {
lappend items [takeList [llength $varList] $generator]
}
try {
# Keep going until all of the generators are exhausted
# This is the foreach behaviour: empty strings are substituted for
# exhausted generators.
while 1 {
set count 0
::foreach {varList generator} $genSpec item $items {
incr count [llength $item]
uplevel 1 [list lassign $item {*}$varList]
}
if {$count == 0} {
# All exhausted
break
}
try {
uplevel 1 $body
} on continue {} {
# Continue processing
} on return {result options} {
# increment -level to remove implementation details
dict incr options -level
return -options $options $result
}
set items [list]
::foreach {varList generator} $genSpec {
lappend items [takeList [llength $varList] $generator]
}
}
} finally {
# Ensure generators are all cleaned up
::foreach {_ generator} $genSpec {
destroy $generator
}
}
return
}
# finally cmd args.. --
#
# Arranges for cmd to be called when the generator is destroyed. This
# can be used to perform cleanup in the event that a generator is
# terminated early.
#
proc finally args {
set ns [uplevel 1 { namespace current }]
trace add command [info coroutine] delete [list ::apply [list args $args $ns]]
}
proc exists generator { expr {[llength [info commands $generator]] != 0} }
proc destroy args {
::foreach generator $args {
if {[exists $generator]} { rename $generator "" }
}
}
proc yield args {
# Each argument is yielded individually as a separate value.
::foreach arg $args {
::yield [list $arg]
}
}
proc define {name params body} {
set name [Resolve 1 $name]
set ns [namespace qualifiers $name]
set lambda [list $params $body $ns]
interp alias {} $name {} ::generator::spawn $lambda
return $name
}
##### PRIVATE METHODS #####
proc spawn {lambda args} {
set it [Gensym]
coroutine $it ::generator::generate $it $lambda $args
}
proc generate {name lambda argList} {
::yield $name
apply $lambda {*}$argList
}
proc Resolve {level name} {
if {[string match ::* $name]} { return $name }
if {[string is integer -strict $level] && $level >= 0} { incr level }
set ns [uplevel $level { namespace current }]
if {$ns eq "::"} { return ::$name }
return $ns\::$name
}
proc All {p xs} {
::foreach x $xs { if {![{*}$p $x]} { return 0 } }
return 1
}
proc Empty? xs { expr {[llength $xs] == 0} }
variable Gensymid 0
proc Gensym {} {
variable Gensymid
set prefix [namespace current]::generator
while {1} {
set name $prefix[incr Gensymid]
if {[llength [info commands $name]] == 0} { break }
}
return $name
}
proc Usage msg {
return -code error -level 2 "wrong # args: should be \"$msg\""
}
proc names {} {
set pat {[0-9]*}
return [info commands [namespace current]::generator$pat]
}
##### STANDARD GENERATORS #####
define map {f xs} {
# Ensure underlying generator is cleaned up too
finally destroy $xs
foreach x $xs { yield [{*}$f $x] }
}
define filter {p xs} {
finally destroy $xs
foreach x $xs {
if {[{*}$p $x]} { yield $x }
}
}
proc reduce {f z xs} {
foreach x $xs { set z [{*}$f $z $x] }
return $z
}
proc foldl {f z xs} { reduce $f $z $xs }
proc foldr {f z xs} {
set ys [generator to list $xs]
for {set i 0} {$i < [llength $ys]} {incr i} {
set z [{*}$f [lindex $ys end-$i] $z]
}
return $z
}
define zipWith {f xs ys} {
finally destroy $xs $ys
foreach x $xs y $ys { yield [{*}$f $x $y] }
}
proc zip {xs ys} { zipWith list $xs $ys }
proc all {p xs} {
and [map $p $xs]
}
proc and xs {
# foldl && true $xs
# more efficient implementation (bail-out on first non-true element):
foreach x $xs { if {!$x} { return 0 } }
return 1
}
proc any {p xs} { reduce or 0 [map $p $xs] }
define concat args {
::foreach xs $args { finally destroy $xs }
::foreach xs $args {
foreach x $xs { yield $x }
}
}
define concatMap {f xs} {
concat {*}[map $f $xs]
}
proc drop {n xs} {
takeList $n $xs
return $xs
}
define dropWhile {p xs} {
finally destroy $xs
foreach x $xs {
if {![{*}$p $x]} { yield $x; break }
}
foreach x $xs { yield $x }
}
proc contains {elem xs} {
foreach x $xs { if {$x eq $elem} { return 1 } }
return 0
}
proc foldl1 {f xs} { foldl $f [take 1 $xs] $xs }
proc foldli {f z xs} {
foreach x $xs { set z [{*}$f [incr i] $z $x] }
return $z
}
proc foldri {f z xs} {
set ys [to list $xs]
for {set i [llength $ys]} {$i > 0} {incr i -1} {
set z [{*}$f [incr j] [lindex $ys $i-1] $z]
}
return $z
}
proc head xs { take 1 $xs }
proc tail xs { drop 1 $xs }
proc last xs {
foreach x $xs { }
return $x
}
define init xs {
finally destroy $xs
set last [head $xs]
foreach x $xs {
yield $last
set last $x
}
}
define take {n xs} {
finally destroy $xs
foreach x $xs {
if {[incr i] >= $n} { break }
yield $x
}
}
define iterate {f x} {
while 1 {
yield $x
set x [{*}$f $x]
}
}
proc Count {x y} { incr x }
proc length xs { foldl Count 0 $xs }
proc or {p xs} {
foreach x $xs { if {[{*}$p $x]} { return 1 } }
return 0
}
proc product xs { foldl ::tcl::mathop::* 1 $xs }
define repeat {n args} {
for {set i 0} {$i < $n} {incr i} {
yield {*}$args
}
}
proc sum xs { foldl ::tcl::mathop::+ 0 $xs }
define takeWhile {p xs} {
finally destroy $xs
foreach x $xs {
if {[{*}$p $x]} { yield $x }
}
}
define splitWhen {p xs} {
finally destroy $xs
set token [list]
foreach x $xs {
if {[{*}$p $x]} {
yield $token
set token [list]
} else {
lappend token $x
}
}
if {[llength $token]} { yield $token }
}
define scanl {f z xs} {
finally destroy $xs
yield $z
foreach x $xs {
set z [{*}$f $z $x]
yield $z
}
}
# from ?list|dict? xs
# Converts a list or dictionary into a generator: over elements or key/value
# pairs.
namespace eval from {
namespace export list dict string
namespace ensemble create
generator define list xs {
foreach x $xs { generator yield $x }
}
generator define dict d {
::dict for {k v} $d { generator yield $k $v }
}
generator define string s {
foreach c [split $s ""] { generator yield $c }
}
}
# to ?list|dict? g
# Converts a generator into a list or dictionary by extracting all elements.
# Dictionaries are created by assuming the generator returns a pair of
# values per element, and using these as the key and value.
namespace eval to {
namespace export list dict string
namespace ensemble create
proc list g {
set xs [::list]
generator foreach x $g { lappend xs $x }
return $xs
}
proc dict g {
set d [dict create]
generator foreach {k v} $g { dict set d $k $v }
return $d
}
proc string g {
set s ""
generator foreach c $g { append s $c }
return $s
}
}
# The conversion functions should follow these identity laws:
# [to list [from list $xs]] == $xs
# [to dict [from dict $xs]] == $xs
}
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