Richard Suchenwirth 2002-07-17 - Since Tcl 8.4, lindex and the new lset command take multiple indices to retrieve or modify an element in a nested list. To complement these two new goodies, here's a recursive lsearch that returns an index list, of the first occurrence of the wanted item, as can be used by lindex or lset, or -1 if the element was not found.
Note that the search goes down as long as an element can be interpreted as a list of more than one element, so intended strings like "John F Kennedy" will also be searched, e.g. for F. Note also that the result often is a list, so comparisons should be limited to == -1 or != -1.
proc lrsearch {list el {prefix {}} } {
set pos [lsearch $list $el]
if {$pos != -1} {return [concat $prefix $pos]}
for {set i 0} {$i<[llength $list]} {incr i} {
set ilist [lindex $list $i]
if {[llength $ilist]>1} {
set pos [lrsearch $ilist $el [concat $prefix $i]]
if {$pos != -1} {return $pos}
}
}
return -1
} % lrsearch {a b {c {d e}}} a
0
% lrsearch {a b {c {d e}}} b
1
% lrsearch {a b {c {d e}}} c
2 0
% lrsearch {a b {c {d e}}} d
2 1 0
% lrsearch {a b {c {d e}}} e
2 1 1
% lrsearch {a b {c {d e}}} f
-1However, nested lists with just one element escape attention:^(
% lrsearch {a {{b c}} d} b
-1
% lrsearch {a {b c} d} b
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