diff --git a/interpreter.php b/interpreter.php
new file mode 100644
index 0000000..36833d9
--- /dev/null
+++ b/interpreter.php
@@ -0,0 +1,327 @@
+<?php
+
+class SBLInterpreter
+{
+  private array $vars = [];
+  private array $lines = [];
+  private int $pc = 0;
+  private array $labels = [];
+  private array $functions = [];
+  private array $keyHandlers = [];
+  private bool $listeningForKeys = false;
+  private bool $waitingForKeyInput = false;
+
+  public function __construct(string $file)
+  {
+    $this->lines = file($file, FILE_IGNORE_NEW_LINES);
+    $this->scanLabels();
+  }
+
+  private function scanLabels(): void
+  {
+    foreach ($this->lines as $i => $line) {
+      $line = trim($line);
+      if (preg_match('/^([A-Za-z_]\w*):$/', $line, $m)) {
+        $this->labels[$m[1]] = $i;
+      }
+      if (preg_match('/^~(\w+)$/', $line, $m)) {
+        $start = $i + 1;
+        $end = $start;
+        while ($end < count($this->lines) && trim($this->lines[$end]) !== '~') {
+          $end++;
+        }
+        $this->functions[$m[1]] = array_slice($this->lines, $start, $end - $start);
+      }
+      if (preg_match('/^on\s+(\w+)$/', $line, $m)) {
+        $start = $i + 1;
+        $end = $start;
+        while ($end < count($this->lines) && trim($this->lines[$end]) !== 'end') {
+          $end++;
+        }
+        $this->keyHandlers[$m[1]] = array_slice($this->lines, $start, $end - $start);
+      }
+    }
+  }
+
+  public function run(): void
+  {
+    $this->listeningForKeys = true;
+    while ($this->pc < count($this->lines)) {
+      $line = trim($this->lines[$this->pc]);
+      try {
+        $this->execLine($line);
+        if ($this->waitingForKeyInput) {
+          $this->handleKeyInput();
+          continue;
+        }
+      } catch (Exception $e) {
+        echo "[ERROR] " . $e->getMessage() . "\n";
+        exit(1);
+      }
+      $this->pc++;
+    }
+  }
+
+  private function execLine(string $line): void
+  {
+    if ($line === '' || $line[0] === '#')
+      return;
+
+    if (preg_match('/^\w+:$/', $line))
+      return;
+
+    if (preg_match('/^\$(.+)$/', $line, $m)) {
+      echo $this->evalExpr($m[1]) . "\n";
+      return;
+    }
+
+    if (preg_match('/^\?(\w+)(?:\s+\"([^\"]+)\")?$/', $line, $m)) {
+      $prompt = $m[2] ?? $m[1];
+      $input = trim(readline("$prompt: "));
+      $this->vars[$m[1]] = is_numeric($input) ? (int) $input : $input;
+      return;
+    }
+
+    if (preg_match('/^(\w+)\[(\d+)\]\s*=\s*(.+)$/', $line, $m)) {
+      $var = $m[1];
+      $index = (int) $m[2];
+      $value = $this->evalMath($m[3]);
+      if (!isset($this->vars[$var]) || !is_array($this->vars[$var])) {
+        $this->vars[$var] = [];
+      }
+      $this->vars[$var][$index] = $value;
+      return;
+    }
+
+    if (preg_match('/^(\w+)\s*=\s*\[(.*)\]$/', $line, $m)) {
+      $arrayItems = array_map('trim', explode(',', $m[2]));
+      $parsed = array_map(function ($item) {
+        if (preg_match('/^\d+$/', $item))
+          return (int) $item;
+        if (preg_match('/^\".*\"$/', $item))
+          return trim($item, '"');
+        return $item;
+      }, $arrayItems);
+      $this->vars[$m[1]] = $parsed;
+      return;
+    }
+
+    if (preg_match('/^(\w+)\s*=\s*(.+)$/', $line, $m)) {
+      $this->vars[$m[1]] = $this->evalMath($m[2]);
+      return;
+    }
+
+    if (preg_match('/^(\w+)\s*:\s*(int|str)$/', $line, $m)) {
+      $result = $this->validate($m[1], $m[2]);
+      $this->vars['__last_validation__'] = $result ? "1" : "0";
+      return;
+    }
+
+    if (preg_match('/^goto\s+(\w+)$/', $line, $m)) {
+      if (!isset($this->labels[$m[1]]))
+        throw new Exception("Label {$m[1]} not found");
+      $this->pc = $this->labels[$m[1]];
+      return;
+    }
+
+    if (preg_match('/^if\s+(.+)$/', $line, $m)) {
+      $cond = $this->evalCond($m[1]);
+      if (!$cond) {
+        $depth = 1;
+        while (++$this->pc < count($this->lines)) {
+          $l = trim($this->lines[$this->pc]);
+          if (preg_match('/^if\s+/', $l))
+            $depth++;
+          if ($l === 'fi') {
+            $depth--;
+            if ($depth === 0)
+              return;
+          }
+          if ($depth === 1 && preg_match('/^elseif\s+/', $l)) {
+            $newCond = $this->evalCond(trim(substr($l, 7)));
+            if ($newCond)
+              return;
+          }
+          if ($depth === 1 && $l === 'else') {
+            return;
+          }
+        }
+      }
+      return;
+    }
+
+    if (preg_match('/^elseif\s+(.+)$/', $line, $m)) {
+      $cond = $this->evalCond($m[1]);
+      if (!$cond) {
+        $depth = 1;
+        while (++$this->pc < count($this->lines)) {
+          $l = trim($this->lines[$this->pc]);
+          if (preg_match('/^if\s+/', $l))
+            $depth++;
+          if ($l === 'fi') {
+            $depth--;
+            if ($depth === 0)
+              return;
+          }
+          if ($depth === 1 && preg_match('/^elseif\s+/', $l)) {
+            $newCond = $this->evalCond(trim(substr($l, 7)));
+            if ($newCond)
+              return;
+          }
+          if ($depth === 1 && $l === 'else') {
+            return;
+          }
+        }
+      }
+      return;
+    }
+
+    if ($line === 'else') {
+      $depth = 1;
+      while (++$this->pc < count($this->lines)) {
+        $l = trim($this->lines[$this->pc]);
+        if (preg_match('/^if\s+/', $l))
+          $depth++;
+        if ($l === 'fi') {
+          $depth--;
+          if ($depth === 0)
+            return;
+        }
+      }
+      return;
+    }
+
+    if ($line === 'fi')
+      return;
+
+    if (preg_match('/^~(\w+)\(\)$/', $line, $m)) {
+      $funcName = $m[1];
+      if (!isset($this->functions[$funcName]))
+        throw new Exception("Undefined function: ~$funcName");
+      foreach ($this->functions[$funcName] as $funcLine) {
+        $this->execLine(trim($funcLine));
+      }
+      return;
+    }
+
+    if (preg_match('/^on\s+(\w+)$/', $line)) {
+      while (++$this->pc < count($this->lines)) {
+        if (trim($this->lines[$this->pc]) === 'end')
+          break;
+      }
+      return;
+    }
+
+    if ($line === ';') {
+      $this->waitingForKeyInput = true;
+      return;
+    }
+
+    throw new Exception("Unknown statement: $line");
+  }
+
+  private function handleKeyInput(): void
+  {
+    system('stty -icanon -echo');
+    $key = fgetc(STDIN);
+    system('stty icanon echo');
+    if ($key !== false && isset($this->keyHandlers[$key])) {
+      foreach ($this->keyHandlers[$key] as $handlerLine) {
+        $this->execLine(trim($handlerLine));
+      }
+    }
+    $this->waitingForKeyInput = false;
+  }
+
+  private function evalExpr(string $expr): string
+  {
+    $parts = preg_split('/\s*\+\s*/', $expr);
+    $out = '';
+    foreach ($parts as $p) {
+      $p = trim($p);
+      if (preg_match('/^"(.*)"$/', $p, $m)) {
+        $out .= $m[1];
+      } elseif (preg_match('/^(\w+)\[(\d+)\]$/', $p, $m)) {
+        $val = $this->vars[$m[1]][(int) $m[2]] ?? '';
+        $out .= $val;
+      } elseif (isset($this->vars[$p])) {
+        $val = $this->vars[$p];
+        $out .= is_array($val) ? json_encode($val) : $val;
+      } elseif (is_numeric($p)) {
+        $out .= $p;
+      } else {
+        throw new Exception("Invalid token in expression: $p");
+      }
+    }
+    return $out;
+  }
+
+  private function evalMath(string $expr): mixed
+  {
+    $expr = preg_replace_callback('/\brandom\((\d+),(\d+)\)/', function ($m) {
+      return random_int((int) $m[1], (int) $m[2]);
+    }, $expr);
+
+    $expr = preg_replace_callback('/\b[a-zA-Z_]\w*(?:\[\d+\])?\b/', function ($matches) {
+      $token = $matches[0];
+      if (preg_match('/^(\w+)\[(\d+)\]$/', $token, $m)) {
+        return is_numeric($this->vars[$m[1]][(int) $m[2]] ?? null) ? (string) ($this->vars[$m[1]][(int) $m[2]]) : '0';
+      } else {
+        return is_numeric($this->vars[$token] ?? null) ? (string) ($this->vars[$token]) : '0';
+      }
+    }, $expr);
+
+    set_error_handler(function () {
+      throw new Exception("Math error in expression.");
+    });
+    $result = eval ("return ($expr);");
+    restore_error_handler();
+    return $result;
+  }
+
+  private function validate(string $var, string $type): bool
+  {
+    if (!isset($this->vars[$var]))
+      return false;
+    $val = trim((string) $this->vars[$var]);
+    return match ($type) {
+      'int' => preg_match('/^[+-]?\d+$/', $val) === 1,
+      'str' => is_string($val),
+      default => false
+    };
+  }
+
+  private function evalCond(string $cond): bool
+  {
+    if (preg_match('/^(\w+)\s*:\s*(\w+)$/', $cond, $m)) {
+      return $this->validate($m[1], $m[2]);
+    }
+
+    $ops = ['==', '!=', '>=', '<=', '>', '<'];
+    foreach ($ops as $op) {
+      if (strpos($cond, $op) !== false) {
+        [$l, $r] = explode($op, $cond, 2);
+        $l = trim($l);
+        $r = trim($r);
+        $lv = $this->vars[$l] ?? $l;
+        $rv = $this->vars[$r] ?? $r;
+        if (is_numeric($lv))
+          $lv = (int) $lv;
+        if (is_numeric($rv))
+          $rv = (int) $rv;
+        return match ($op) {
+          '==' => $lv == $rv,
+          '!=' => $lv != $rv,
+          '>=' => $lv >= $rv,
+          '<=' => $lv <= $rv,
+          '>' => $lv > $rv,
+          '<' => $lv < $rv,
+        };
+      }
+    }
+    throw new Exception("Invalid condition: $cond");
+  }
+}
+
+$it = new SBLInterpreter("program.sbl");
+$it->run();
\ No newline at end of file
diff --git a/program.sbl b/program.sbl
new file mode 100644
index 0000000..697f75c
--- /dev/null
+++ b/program.sbl
@@ -0,0 +1,16 @@
+start:
+?input "What do you want to oopify?"
+$input + "oop!"
+$"Do you want to oopify something else? (y/n)"
+;
+
+on y
+goto start
+end
+
+on n
+goto end
+end
+
+end:
+$"Goodbye!"
\ No newline at end of file