CODEWITHSUNDEEP
tcl
pax
pax

Reputation: 90

Accessing list-of-lists returned from tcl procedure

I have a procedure that returns a list of lists. I can't figure out how to access the inner lists without splitting them first. I'm sure there must be a cleaner way.

For example, this:

proc return_l_of_l {} {
  set x {a b c}
  set y {d e f}
  return [list [list $x] [list $y]]
}
set l [return_l_of_l]
set x_list [lindex $l 0]
set y_list [lindex $l 1]

foreach x $x_list { puts $x }
foreach y $y_list { puts $y }

outputs:

a b c
d e f

not:

a
b
c
d
e
f

Upvotes: 0

Views: 1767

Answers (2)

kostix
kostix

Reputation: 55453

proc return_l_of_l {} {
  set x {a b c}
  set y {d e f}
  return [list [list $x] [list $y]]
}

returns a list of two lists each consisting of a single element — a b c and d e f. That's because {a b c} and {d e f} are already constructs which can be interpreted as lists.

Supposedly you'd just need

return [list $x $y]

Upvotes: 0

Donal Fellows
Donal Fellows

Reputation: 137567

The problem is this line:

return [list [list $x] [list $y]]

Since x and y already hold lists, it makes a list of lists of lists. You should instead do:

return [list $x $y]

or possibly:

return [list [list {*}$x] [list {*}$y]]

Upvotes: 3

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