Inserting single curly braces to Tcl list elements - tcl

Question

I have a report file having multiple lines in this form:
str1 num1 num2 ... numN str2
Given that (N) is not the same across lines. These numbers represent coordinates, so I need to enclose each point with curly braces to be:
{num1 num2} {num3 num4} and so on...
I have tried this piece of code:
set file_r [open file.rpt r]
set lines [split [read $file_r] "\n"]
close $file_r
foreach line $lines {
set items [split $line]
set str1 [lindex $items 0]
set str2 [lindex $items [expr [llength $items] - 1]]
set box [lrange $items 1 [expr [llength $items] - 2]]
foreach coord $box {
set index [lsearch $box $coord]
set index_rem [expr $index % 2]
if {index_rem == 0} {
set box [lreplace $box $index $index "{$coord"]
} else {
set box [lreplace $box $index $index "$coord}"]
}
}
puts "box: $box"
}
This gives me a syntax error that a close-brace is missing. And if I try "\{$coord" the back-slash character gets typed in the $box.
Any ideas to overcome this?

Answer 1

There are a few things you could improve to have better and simpler Tcl style.
You usually don't need to use split to form a list from a line if the line is already space separated. Space separated strings can almost always be used directly in list commands.
The exceptions are when the string contains { or " characters.
lindex and lrange can take end and end-N arguments.
This plus Donal's comment to use lmap will result in this:
set file_r [open file.rpt r]
set lines [split [read $file_r] "\n"]
close $file_r
foreach line $lines {
set str1 [lindex $line 0]
set str2 [lindex $line end]
set numbers [lrange $line 1 end-1]
set boxes [lmap {a b} $numbers {list $a $b}]
foreach box $boxes {
puts "box: {$box}"
}
}