TCL assign and evaluate a variable in boolean conditional seems to fail

In a while conditional I am read-assigning and then testing a variable as boolean expression.

Let's say I am reading a file and want to discard lines that are comments. Yet the following does not enter the loop. The puts never prints.

while {[gets $fp line] >= 0 && [regexp {^#} $line] ==0} {
  puts "Got valid data"
}

Seems the gets assignment of line and it's evaluation can't be in the same conditional. Is that corroborated in TCL spec?

For sure this one works but I would have liked to do the conditional in one statement.

while {[gets $fp line] >= 0 } {
  if {[regexp {^#} $line] == 0 } {
    puts "Got valid data"
  }
}

Cheers.

as per @glennjackman, logic is flawed.

here's a trivial example using a function to read/filter input

cat gert.tcl
#!/usr/bin/env tclsh

proc filteredRead {fstream lineVar prune} {
    upvar $fstream handle;
    upvar $lineVar line;
    upvar $prune   filter; #skip lines matching this regexp

    while {[gets $fstream line] >= 0} {
        if {[regexp $prune $line]} {
            continue
        }
        return 1
    }
    return 0
}

if {$argc == 0} {
    puts "Usage: $argv0 <filename> [filter (default is ^#)]"
    exit 1
}

set filename [lindex $argv 0]
set filter {^#};     # default filter is comment lines

if {$argc == 2} {
    set filter [lindex $argv 1]
}

if {![file readable $filename]} {
    puts "Error: File '$filename' does not exist or is not readable."
    exit 1
}

set handle [open $filename r]

set line ""

puts "\nfiltering lines matching: \[$filter\]"

while {[filteredRead $handle line $filter]} {
    puts "\[$line\]"
}

close $handle

#
#invoke against an simple test file 
#
cat input
# i'm a comment, skip me
print me 

# i'm also comment, skip me
and me
# skip me 

# and me
i will be printed
# i'll be skipped

./gert.tcl input
filtering lines matching: [^#]
[print me ]
[]
[and me]
[]
[i will be printed]

hope this helps.