Attempt to create nested for loops generating missing arguments error

Am attempting to teach myself to program using Tcl. (I want to become more familiar with the language to understand someone else's code - SCID chess) The task i've set myself to motivate my learing of Tcl is to solve the 开发者_StackOverflow8 queens problem. My approach to creating a program is to sucessively 'prototype' a solution. So. I'm up to nesting a for loop holding the q pos on row 2 inside the for loop holding the q pos on row 1

Here is my code

set allowd 1
set notallowd 0

for {set r1p 1} {$r1p <= 8} {incr r1p } {
    puts "1st row q placed at $r1p" 
    ;# re-initialize r2 'free for q placemnt' array after every change of r1 q pos:
    for {set i 1 } {$i <= 8} {incr i} { set r2($i) $allowd    }

    for { set r2($r1p) $notallowd ; set r2([eval $r1p-1]) $notallowd ;
           set r2([eval $r1p+1]) $notallowd ; set r2p 1}   {$r2p <= 8} {
         incr r2p ;# end of 'next' arg of r2 forloop
        }
        ;# commnd arg of r2 forloop placed below: 
        {puts "2nd row q placed at $r2p"    
    }
} 

My problem is that when i run the code the interpreter is aborting with the fatal error: "wrong #args should be for start test next command.

I've gone over my code a few times and can't see that i've missed any of the for loop arguments.

The carriage return before the command in the last for loop is what's getting you. From the first syntax rule on the Tcl man page, "Semi-colons and newlines are command separators unless quoted as described below." BTW, your eval's should be expr's.

This works for me:

set allowd 1
set notallowd 0

for {set r1p 1} {$r1p <= 8} {incr r1p } {
    puts "1st row q placed at $r1p" 
    ;# re-initialize r2 'free for q placemnt' array after every change of r1 q pos:
    for {set i 1 } {$i <= 8} {incr i} { set r2($i) $allowd    }

    for { set r2($r1p) $notallowd ; set r2([expr $r1p-1]) $notallowd ;
        set r2([expr $r1p+1]) $notallowd ; set r2p 1}   {$r2p <= 8} {
        incr r2p ;# end of 'next' arg of r2 forloop
    } {
        # commnd arg of r2 forloop placed below: 
        puts "2nd row q placed at $r2p"    
    }
}