#!/usr/bin/perl

use strict;
use warnings;
$SIG{__WARN__} = sub { die $@ };

for my $row (
  { a => 1, b => 2, c => 3, d => 4 },
  { a => 0, b => 2, c => 3, d => 4 },
  { a => 0, b => 2, c => 2, d => 4 },
  { a => 0, b => 2, c => 2, d => 3 },
  )
  {
  use Data::Dump 'dd'; dd 'row', $row;
  for my $test ( qw( a>0 a>1 a>2 a>3 d<=3 c>2&d>2 ) )
    {
    use Data::Dump 'dd'; dd { $test => nonevalRow($test, $row) };
    }
  print "\n";
  }

my $dictionary;
sub error { die $_, s/\G.*//sr =~ tr/\t/ /cr, "^ $_[0] !\n" }
sub want { /\G$_[1]/gc ? shift : error pop }

sub nonevalRow
  {
  ( local $_, $dictionary ) = @_;
  $_ .= "\n";
  return want(expr(0), "\n", 'Incomplete Parse');
  }

sub expr
  {
  /\G\h+/gc;
  my $value =
    /\G\d+/gc ? "$&" :
    /\G[a-z]\w*/gci ? $dictionary->{"$&"} // error("undefined variable '$&' ") :
    /\G\(/gc  ? want expr(0), qr/\)/, 'Missing Right Paren' :
    /\G\-/gc  ? - expr(7) : # unary minus
    /\G\+/gc  ? + expr(7) : # unary plus
    error 'Operand Expected';
  $value =
    /\G\h+/gc                 ? $value            :
    $_[0] <= 6 && /\G\*\*/gcx ? $value ** expr(6) :
    $_[0] <= 5 && /\G \* /gcx ? $value *  expr(6) :
    $_[0] <= 5 && /\G \/ /gcx ? $value /  expr(6) :
    $_[0] <= 4 && /\G \+ /gcx ? $value +  expr(5) :
    $_[0] <= 4 && /\G \- /gcx ? $value -  expr(5) :
    $_[0] <= 3 && /\G  <=/gcx ? $value <= expr(4) ? 1 : 0 :
    $_[0] <= 3 && /\G  >=/gcx ? $value >= expr(4) ? 1 : 0 :
    $_[0] <= 3 && /\G  < /gcx ? $value <  expr(4) ? 1 : 0 :
    $_[0] <= 3 && /\G  > /gcx ? $value >  expr(4) ? 1 : 0 :
    $_[0] <= 2 && /\G  ==/gcx ? $value == expr(3) ? 1 : 0 :
    $_[0] <= 2 && /\G  !=/gcx ? $value != expr(3) ? 1 : 0 :
    $_[0] <= 1 && /\G  & /gcx ? $value &  expr(2) :
    $_[0] <= 0 && /\G  \|/gcx ? $value |  expr(1) :
    return $value while 1;
  }