Tcl Source Code

"mapeach" is a collecting [foreach], and arises from a discussion at http://wiki.tcl.tk/26013 .  This patch provides an implementation of [mapeach] in the core, with full bytecoding support, leveraging the existing [foreach] infrastructure.

Variation of this incorporated into 8.6 as lmap.

Latest implementation committed to branch 'tip-405-impl-td'.  This includes 'mapeach' and 'dict map' with full test suites, a bug fix made since the last patchfile, and man pages.

Also included is an experimental accumulating foreach tentatively named 'foreacha'.  [foreacha] treats the first list variable as an accumulator.  The accumulator consumes a list element on the first iteration only, and is returned by [foreacha].

Examples of [foreacha]:

fold with initial var: foreacha a 0 b {1 2 3 4} { incr a $b }
fold without initial var: foreacha {a b} {1 2 3 4} { incr a $b }
filter: foreacha a {} b {1 2 3 4} { if { ($b % 2)==0 } { lappend a $b } }
map: foreacha a {} b {1 2 3 4} { lappend a [expr { $b * 5 }] }
prefix: foreacha a {} b {1 2 3 4} { if { $b > 2 } break; lappend a $b }

# Performance tests
# Tcl = 32-bit tclsh86t.exe from trunk [19174445] with branches bug-3545363
#       and td-mapeach merged in, built with MSVC10, OPTS=threads
# Platform = Intel64 (AMD64) i5 @ 2.67Ghz running Windows 7 (64-bit)

set d [lsearch -all [lrepeat 1000000 x] x] ; llength $d

lindex $d 1000 ;# ensure list rep

time {
set accum {}
foreach {k v} $::d {
  lappend accum [expr { $k * $v }]
}
puts [tcl::mathop::+ {*}$accum] ;# 166666416666500000
}
# 750919 microseconds per iteration (foreach)

time {
puts [tcl::mathop::+ {*}[mapeach {k v} $::d { expr { $k * $v } }]] ;# 166666416666500000
}
# 616432 microseconds per iteration (mapeach)

time { 
apply {{} {
set accum {}
foreach {k v} $::d {
  lappend accum [expr { $k * $v }]
}
puts [tcl::mathop::+ {*}$accum] ;# 166666416666500000
}}
}
# 382724 microseconds per iteration (apply foreach)

time {
apply {{} {
puts [tcl::mathop::+ {*}[mapeach {k v} $::d { expr { $k * $v } }]] ;# 166666416666500000
}}
}
# 382829 microseconds per iteration (apply mapeach)

dict get $d 1000 ;# ensure dict rep

time {
set accum {}
dict for {k v} $::d {
  lappend accum [expr { $k * $v }]
}
puts [tcl::mathop::+ {*}$accum] ;# 166666416666500000
}
# 739547 microseconds per iteration (dict for)

time {
puts [tcl::mathop::+ {*}[dict map {k v} $::d { expr { $k * $v } }]] ;# 166666416666500000
}
# 621000 microseconds per iteration (dict map)

time { 
apply {{} {
set accum {}
dict for {k v} $::d {
  lappend accum [expr { $k * $v }]
}
puts [tcl::mathop::+ {*}$accum] ;# 166666416666500000
}}
}
# 357713 microseconds per iteration (apply dict for)

time {
apply {{} {
puts [tcl::mathop::+ {*}[dict map {k v} $::d { expr { $k * $v } }]] ;# 166666416666500000
}}
}
# 360457 microseconds per iteration (apply dict map)

RANK:
# 357713 microseconds per iteration (apply dict for)
# 360457 microseconds per iteration (apply dict map)
# 382724 microseconds per iteration (apply foreach)
# 382829 microseconds per iteration (apply mapeach)
# 616432 microseconds per iteration (mapeach)
# 621000 microseconds per iteration (dict map)
# 739547 microseconds per iteration (dict for)
# 750919 microseconds per iteration (foreach)

File Added - 450402: td-3163961-3.patch

File Added - 450233: td-3163961-2.patch

Includes a full set up tests (partially derived from the foreach.test suite).

File Added - 399514: mapeach.test

File Added - 399513: mapeach.patch