This is a drop-in replacement for the standard for command. It supports an expanded syntax for looping over iterators, and is fully compatible with the standard for command. It can be downloaded as a part of ycl, or copied straight from this page. The [package require] command is not required, but indicates how to use this command as part of ycl.
package require ycl::iter
for {varname1 ...} in iterator_name1 [{varname {varnameX ... } in iterator_nameX] ... script like foreach does with list, it can operate on multiple iterators and take an arbitrary number of items each time from each iterator. Also like foreach, empty strings are produced as necessary for any iterator which becomes depleted before the others.
note that [return -code break] within an iterator will cause the for loop to break, so it should be used with care.
newer code may be available in the ycl repository
rename ::for for_core
interp alias {} ::for {} [namespace current]::for
proc for args {
if {[lindex $args 1] eq "in"} {
if {[llength $args] % 3 != 1} {
return -code error "wrong number of arguments for [info level 0]"
}
set assigns {}
set assign_template {
if {[namespace which $iter] eq {}} {
variable $varname {}
} else {
variable $varname [$iter]
}
}
set conditions {}
set condition_template {[namespace which $iter] ne {}}
while {[llength $args] > 1} {
set args [lassign $args[unset args] varnames {} iter]
foreach varname $varnames {
lappend assigns [string map [list \$iter [list $iter] \$varname [list $varname]] \
$assign_template]
}
lappend conditions [string map [list \$iter [list $iter]] $condition_template]
}
set assigns [join $assigns \n]
set args [join $args \n]
uplevel "while {[join $conditions { || }]} {
$assigns
if {!([join $conditions { || }])} {
break
}
$args
}"
} else {
uplevel [list [namespace current]::for_core {*}$args]
}
}
namespace eval basket {
set items [list apples oranges bananas kiwis pears]
set current 0
proc next {} {
variable items
variable current
if {$current < [llength $items]} {
return [lindex $items [expr {[incr current]-1}]]
}
rename [info level 0] {}
}
}
set result [list]
for fruit in basket::next {
lappend result $fruit
}
puts $resultproduces
apples oranges bananas kiwis pears
example
set result [list]
for {key val} in [coroutine students apply {{} {
yield [info coroutine]
set db {
Jack 97
Sally 89
Bob 83
Jill 77
John 72
}
set index -1
foreach {name score} $db {
yield $name
yield $score
}
}}] prize in [coroutine prizes apply {{} {
yield [info coroutine]
foreach item { first second third } {
yield $item
}
}}] {
lappend result $key $val $prize
}
puts $resultproduces:
Jack 97 first Sally 89 second Bob 83 third Jill 77 {} John 72 {}