Print List in Reverse: TCL

Question

I am reading "Exploring Expect: A TCL-Based Toolkit ... " by Don Libes.

An end of chapter question asked to "Write a procedure to reverse a string. If you wrote an iterative solution, now write a recursive solution or vice versa."

Reading up to this point in time, I decided to try the following:

set list {a b c d e f g}


for {set index [expr [llength $list]-1]} {$index>=0} {incr $index - 1} {

for {set i [expr [llength $list]-1]} {$i>=0} {incr $i - 1} {

    puts [lindex $list $index]

}

}

But I get the following error:

Error(s), warning(s):
wrong # args: should be "incr varName ?increment?"
    while executing
"incr $i - 1"
    ("for" body line 3)
    invoked from within
"for {set index [expr [llength $list]-1]} {$index>=0} {incr $index - 1} {

for {set i [expr [llength $list]-1]} {$i>=0} {incr $i - 1} {

    puts [lind..."
    (file "source_file.tcl" line 4)
g

I see that I am not incrimenting the "index" variable correctly though I am unsure as to why. Also, is this approach recursive or iterative?

Any advice will be greatly appreciated.

---

________SOLUTION____________________________________

Based on the solution/approach provided by @glenn the correct code is as follows:

set list {a b c d e f g}



for {set i [expr {[llength $list]-1}]} {$i>=0} {incr i -1} {

    puts [lindex $list $i]

}

Many other examples are shown by his post below.

Answer 1

First thing, you are passing 3 arguments to incr: $index, - and 1. As the error message indicates, incr takes a maximum of 2 arguments. Specify "minus 1" as -1 with no spaces.

Take careful note of the error message:

wrong # args: should be "incr varName ?increment?"

Note how it says varName -- when you use $index you are passing the variable's value not the name. Remove the $

for {set i [expr {[llength $list]-1}]} {$i>=0} {incr i -1} {
# .................................................. ^ ^^
#                                              varname increment

Note the braces around the argument to expr: that's a good habit to get into.