#!/usr/bin/perl -w

use strict;

#variables
my $times = $ARGV[0] || 5;
my $depth = $ARGV[1] || 5;
my $value_limit = 10;
my @letters = ('a' .. 'z');
my @operators = qw(+ - * /);
my @variables = (); 
my %variables = ();

#main
for my $i (1 .. $times){
    generate_variables($depth); #this may go outside the for loop
    my ($expression,$value) = expression($depth);
    print "Expression: $expression\n";
    print "Value: $value\n";
}

#subs
sub randelm { return $_[int rand @_]; }

sub generate_variables {
    my $depth = shift;
    for my $i (0 .. $depth - 1){
    my $name = $letters[$i % 26] x (int $i / 26  + 1); # such as "aaa"
+;
    my $value = (rand $value_limit) + 1;               # such as 3.2; 
    $variables[$i][0] = $name;    # @varibles = ([$name,$value],
    $variables[$i][1] = $value;   #              [$name,$value]...)
    $variables{$name} = $value;   # A hash of names and values.
    }
}

sub expression {
    my $depth = shift;
    if($depth == 0){ #base case
    return @{randelm(@variables)};
    } else {        
    my @left = expression(int rand($depth - 1));
    my @right = expression(int rand($depth - 1));
    my $operator = randelm(@operators);
    my $name = "($left[0] $operator $right[0])";
    my $value = "($left[1] $operator $right[1])";
    return ($name, eval $value);
    }
}
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