Merge branch 'main' into issue-3911issue-3911

23 files changed, 1344 insertions, 0 deletions

diff --git a/lib/exTpl/ArithExpression.php b/lib/exTpl/ArithExpression.php
new file mode 100644
index 0000000..4888b73
--- /dev/null
+++ b/lib/exTpl/ArithExpression.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * ArithExpression represents an arithmetic operator.
+ */
+class ArithExpression extends BinaryExpression
+{
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context symbol table
+     */
+    public function value(Context $context): mixed
+    {
+        $left  = $this->left->value($context);
+        $right = $this->right->value($context);
+
+        return match ($this->operator) {
+            '+' => $left + $right,
+            '-' => $left - $right,
+            '*' => $left * $right,
+            '/' => $left / $right,
+            '%' => $left % $right,
+            '~' => $left . $right,
+        };
+    }
+}
diff --git a/lib/exTpl/ArrayNode.php b/lib/exTpl/ArrayNode.php
new file mode 100644
index 0000000..3981598
--- /dev/null
+++ b/lib/exTpl/ArrayNode.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * ArrayNode represents a sequence of arbitrary nodes.
+ */
+class ArrayNode implements Node
+{
+    protected array $nodes = [];
+
+    /**
+     * Adds a child node to this sequence node.
+     *
+     * @param Node $node child node to add
+     */
+    public function addChild(Node $node): void
+    {
+        $this->nodes[] = $node;
+    }
+
+    /**
+     * Returns a string representation of this node.
+     *
+     * @param Context $context symbol table
+     */
+    public function render(Context $context): string
+    {
+        $result = '';
+
+        foreach ($this->nodes as $node) {
+            $result .= $node->render($context);
+        }
+
+        return $result;
+    }
+}
diff --git a/lib/exTpl/BinaryExpression.php b/lib/exTpl/BinaryExpression.php
new file mode 100644
index 0000000..1c82730
--- /dev/null
+++ b/lib/exTpl/BinaryExpression.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * BinaryExpression represents a binary operator.
+ */
+abstract class BinaryExpression implements Expression
+{
+    protected Expression $left;
+    protected Expression $right;
+    protected mixed $operator;
+
+    /**
+     * Initializes a new Expression instance.
+     *
+     * @param Expression $left left operand
+     * @param Expression $right right operand
+     * @param mixed $operator operator token
+     */
+    public function __construct(Expression $left, Expression $right, mixed $operator)
+    {
+        $this->left     = $left;
+        $this->right    = $right;
+        $this->operator = $operator;
+    }
+}
diff --git a/lib/exTpl/BooleanExpression.php b/lib/exTpl/BooleanExpression.php
new file mode 100644
index 0000000..0e18df0
--- /dev/null
+++ b/lib/exTpl/BooleanExpression.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * BooleanExpression represents a boolean operator.
+ */
+class BooleanExpression extends BinaryExpression
+{
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context symbol table
+     */
+    public function value(Context $context): bool
+    {
+        $left  = $this->left->value($context);
+        $right = $this->right->value($context);
+
+        return match ($this->operator) {
+            T_IS_EQUAL            => $left == $right,
+            T_IS_NOT_EQUAL        => $left != $right,
+            '<'                   => $left < $right,
+            T_IS_SMALLER_OR_EQUAL => $left <= $right,
+            '>'                   => $left > $right,
+            T_IS_GREATER_OR_EQUAL => $left >= $right,
+            T_BOOLEAN_AND         => $left && $right,
+            T_BOOLEAN_OR          => $left || $right,
+        };
+    }
+}
diff --git a/lib/exTpl/ConditionExpression.php b/lib/exTpl/ConditionExpression.php
new file mode 100644
index 0000000..657ee31
--- /dev/null
+++ b/lib/exTpl/ConditionExpression.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * ConditionExpression represents the conditional operator ('?:').
+ */
+class ConditionExpression implements Expression
+{
+    protected Expression $condition;
+    protected Expression $left;
+    protected Expression $right;
+
+    /**
+     * Initializes a new Expression instance.
+     *
+     * @param Expression $condition expression
+     * @param Expression $left left alternative
+     * @param Expression $right right alternative
+     */
+    public function __construct(Expression $condition, Expression $left, Expression $right)
+    {
+        $this->condition = $condition;
+        $this->left      = $left;
+        $this->right     = $right;
+    }
+
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context symbol table
+     */
+    public function value(Context $context): mixed
+    {
+        return $this->condition->value($context) ?
+            $this->left->value($context) : $this->right->value($context);
+    }
+}
diff --git a/lib/exTpl/ConditionNode.php b/lib/exTpl/ConditionNode.php
new file mode 100644
index 0000000..bab2121
--- /dev/null
+++ b/lib/exTpl/ConditionNode.php
@@ -0,0 +1,59 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * ConditionNode represents a single condition tag:
+ * "{if CONDITION}...{else}...{endif}".
+ */
+class ConditionNode extends ArrayNode
+{
+    protected Expression $condition;
+    protected ArrayNode|null $else_node = null;
+
+    /**
+     * Initializes a new Node instance with the given expression.
+     *
+     * @param Expression $condition expression object
+     */
+    public function __construct(Expression $condition)
+    {
+        $this->condition = $condition;
+    }
+
+    /**
+     * Adds an else block to this condition node.
+     */
+    public function addElse(): void
+    {
+        $this->else_node = new ArrayNode();
+    }
+
+    /**
+     * Adds a child node to this condition node.
+     *
+     * @param Node $node child node to add
+     */
+    public function addChild(Node $node): void
+    {
+        if ($this->else_node) {
+            $this->else_node->addChild($node);
+        } else {
+            parent::addChild($node);
+        }
+    }
+
+    /**
+     * Returns a string representation of this node.
+     *
+     * @param Context $context symbol table
+     */
+    public function render(Context $context): string
+    {
+        if ($this->condition->value($context)) {
+            return parent::render($context);
+        }
+
+        return $this->else_node ? $this->else_node->render($context) : '';
+    }
+}
diff --git a/lib/exTpl/ConstantExpression.php b/lib/exTpl/ConstantExpression.php
new file mode 100644
index 0000000..7235647
--- /dev/null
+++ b/lib/exTpl/ConstantExpression.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * ConstantExpression represents a literal value.
+ */
+class ConstantExpression implements Expression
+{
+    protected mixed $value;
+
+    /**
+     * Initializes a new Expression instance.
+     *
+     * @param mixed $value expression value
+     */
+    public function __construct(mixed $value)
+    {
+        $this->value = $value;
+    }
+
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context symbol table
+     */
+    public function value(Context $context): mixed
+    {
+        return $this->value;
+    }
+}
diff --git a/lib/exTpl/Context.php b/lib/exTpl/Context.php
new file mode 100644
index 0000000..309174f
--- /dev/null
+++ b/lib/exTpl/Context.php
@@ -0,0 +1,77 @@
+<?php
+/**
+ * Context.php - template parser symbol table
+ *
+ * A Context object represents the symbol table used to resolve
+ *  symbol names to their values in the local scope. Each context
+ *  may inherit symbol definitions from its parent context.
+ *
+ * @copyright 2013  Elmar Ludwig
+ * @license GPL2 or any later version
+ */
+
+namespace exTpl;
+
+use Closure;
+
+class Context
+{
+    private array $bindings;
+    private Closure|null $escape;
+    private Context|null $parent;
+
+    /**
+     * Initializes a new Context instance with the given bindings.
+     *
+     * @param array $bindings symbol table
+     * @param Context|null $parent parent context (or NULL)
+     */
+    public function __construct(array $bindings, Context $parent = null)
+    {
+        $this->bindings = $bindings;
+        $this->parent   = $parent;
+    }
+
+    /**
+     * Looks up the value of a symbol in this context and returns it.
+     * The reserved symbol "this" is an alias for the current context.
+     *
+     * @param string $key symbol name
+     */
+    public function lookup(string $key): mixed
+    {
+        if (isset($this->bindings[$key])) {
+            return $this->bindings[$key];
+        } else if ($this->parent) {
+            return $this->parent->lookup($key);
+        }
+
+        return null;
+    }
+
+    /**
+     * Enables or disables automatic escaping for template values.
+     *
+     * @param callable|null $escape escape callback or null
+     */
+    public function autoescape(?callable $escape): void
+    {
+        $this->escape = $escape ? $escape(...) : null;
+    }
+
+    /**
+     * Escapes the given value using the configured strategy.
+     *
+     * @param mixed $value expression value
+     */
+    public function escape(mixed $value): mixed
+    {
+        if (isset($this->escape)) {
+            $value = call_user_func($this->escape, $value);
+        } else if ($this->parent) {
+            $value = $this->parent->escape($value);
+        }
+
+        return $value;
+    }
+}
diff --git a/lib/exTpl/Expression.php b/lib/exTpl/Expression.php
new file mode 100644
index 0000000..15a485d
--- /dev/null
+++ b/lib/exTpl/Expression.php
@@ -0,0 +1,27 @@
+<?php
+/*
+ * Expression.php - template parser expression interface and classes
+ *
+ * Copyright (c) 2013  Elmar Ludwig
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ */
+
+namespace exTpl;
+
+/**
+ * Basic interface for expressions in the template parse tree. The
+ * only required method is "value" to get the expression's value.
+ */
+interface Expression
+{
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context  symbol table
+     */
+    public function value(Context $context): mixed;
+}
diff --git a/lib/exTpl/ExpressionNode.php b/lib/exTpl/ExpressionNode.php
new file mode 100644
index 0000000..061edce
--- /dev/null
+++ b/lib/exTpl/ExpressionNode.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * ExpressionNode represents an expression tag: "{...}".
+ */
+class ExpressionNode implements Node
+{
+    protected Expression $expr;
+
+    /**
+     * Initializes a new Node instance with the given expression.
+     *
+     * @param Expression $expr expression object
+     */
+    public function __construct(Expression $expr)
+    {
+        $this->expr = $expr;
+    }
+
+    /**
+     * Returns a string representation of this node.
+     *
+     * @param Context $context symbol table
+     */
+    public function render(Context $context): ?string
+    {
+        $value = $this->expr->value($context);
+
+        if (!($this->expr instanceof RawExpression)) {
+            $value = $context->escape($value);
+        }
+
+        return $value;
+    }
+}
diff --git a/lib/exTpl/FunctionExpression.php b/lib/exTpl/FunctionExpression.php
new file mode 100644
index 0000000..48d4413
--- /dev/null
+++ b/lib/exTpl/FunctionExpression.php
@@ -0,0 +1,45 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * FunctionExpression represents a function call.
+ */
+class FunctionExpression implements Expression
+{
+    protected Expression $name;
+    protected array $arguments;
+
+    /**
+     * Initializes a new Expression instance.
+     *
+     * @param Expression $name function name
+     * @param array $arguments function arguments
+     */
+    public function __construct(Expression $name, array $arguments)
+    {
+        $this->name      = $name;
+        $this->arguments = $arguments;
+    }
+
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context symbol table
+     */
+    public function value(Context $context): mixed
+    {
+        $callable  = $this->name->value($context);
+        $arguments = [];
+
+        foreach ($this->arguments as $expr) {
+            $arguments[] = $expr->value($context);
+        }
+
+        if (is_callable($callable)) {
+            return $callable(...$arguments);
+        }
+
+        return null;
+    }
+}
diff --git a/lib/exTpl/IndexExpression.php b/lib/exTpl/IndexExpression.php
new file mode 100644
index 0000000..ecb3241
--- /dev/null
+++ b/lib/exTpl/IndexExpression.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * IndexExpression represents the array index operator.
+ */
+class IndexExpression extends BinaryExpression
+{
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context symbol table
+     */
+    public function value(Context $context): mixed
+    {
+        $left  = $this->left->value($context);
+        $right = $this->right->value($context);
+
+        return $left[$right];
+    }
+}
diff --git a/lib/exTpl/IteratorNode.php b/lib/exTpl/IteratorNode.php
new file mode 100644
index 0000000..58dd593
--- /dev/null
+++ b/lib/exTpl/IteratorNode.php
@@ -0,0 +1,55 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * IteratorNode represents a single iterator tag:
+ * "{foreach ARRAY [as [KEY =>] VALUE]}...{endforeach}".
+ */
+class IteratorNode extends ArrayNode
+{
+    protected Expression $expr;
+    protected string $key_name;
+    protected string $val_name;
+
+    /**
+     * Initializes a new Node instance with the given expression.
+     *
+     * @param Expression $expr expression object
+     * @param string $key_name name of variable on each iteration
+     * @param string $val_name name of variable on each iteration
+     */
+    public function __construct(Expression $expr, string $key_name, string $val_name)
+    {
+        $this->expr     = $expr;
+        $this->key_name = $key_name;
+        $this->val_name = $val_name;
+    }
+
+    /**
+     * Returns a string representation of this node. The IteratorNode
+     * renders the node sequence for each value in the expression list.
+     *
+     * @param Context $context symbol table
+     */
+    public function render(Context $context): string
+    {
+        $values = $this->expr->value($context);
+        $result = '';
+
+        if (is_array($values) && is_int(key($values))) {
+            $bindings = [$this->key_name => &$key, $this->val_name => &$value];
+            $context  = new Context($bindings, $context);
+
+            foreach ($values as $key => $value) {
+                $result .= parent::render(new Context($value, $context));
+            }
+        } else if (is_array($values) && count($values)) {
+            return parent::render(new Context($values, $context));
+        } else if ($values) {
+            return parent::render($context);
+        }
+
+        return $result;
+    }
+}
diff --git a/lib/exTpl/MinusExpression.php b/lib/exTpl/MinusExpression.php
new file mode 100644
index 0000000..6b81e91
--- /dev/null
+++ b/lib/exTpl/MinusExpression.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * MinusExpression represents the unary minus operator ('-').
+ */
+class MinusExpression extends UnaryExpression
+{
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context  symbol table
+     */
+    public function value(Context $context): mixed
+    {
+        return -$this->expr->value($context);
+    }
+}
diff --git a/lib/exTpl/Node.php b/lib/exTpl/Node.php
new file mode 100644
index 0000000..5c24cab
--- /dev/null
+++ b/lib/exTpl/Node.php
@@ -0,0 +1,28 @@
+<?php
+/*
+ * Node.php - template parser node interface and classes
+ *
+ * Copyright (c) 2013  Elmar Ludwig
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ */
+
+namespace exTpl;
+
+
+/**
+ * Basic interface for nodes in the template parse tree. The only
+ * required method is "render" to render a node and its children.
+ */
+interface Node
+{
+    /**
+     * Returns a string representation of this node.
+     *
+     * @param Context $context symbol table
+     */
+    public function render(Context $context): ?string;
+}
diff --git a/lib/exTpl/NotExpression.php b/lib/exTpl/NotExpression.php
new file mode 100644
index 0000000..cf7472d
--- /dev/null
+++ b/lib/exTpl/NotExpression.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * NotExpression represents the logical negation operator ('!').
+ */
+class NotExpression extends UnaryExpression
+{
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context symbol table
+     */
+    public function value(Context $context): bool
+    {
+        return !$this->expr->value($context);
+    }
+}
diff --git a/lib/exTpl/RawExpression.php b/lib/exTpl/RawExpression.php
new file mode 100644
index 0000000..275f239
--- /dev/null
+++ b/lib/exTpl/RawExpression.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * RawExpression represents the "raw" filter function.
+ */
+class RawExpression extends UnaryExpression
+{
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context symbol table
+     */
+    public function value(Context $context): mixed
+    {
+        return $this->expr->value($context);
+    }
+}
diff --git a/lib/exTpl/Scanner.php b/lib/exTpl/Scanner.php
new file mode 100644
index 0000000..76cbc01
--- /dev/null
+++ b/lib/exTpl/Scanner.php
@@ -0,0 +1,87 @@
+<?php
+/**
+ * Scanner.php - template parser lexical scanner
+ *
+ * Simple wrapper class around the Zend engine's lexical scanner. It
+ *  automatically skips whitespace.
+ *
+ * @copyright 2013  Elmar Ludwig
+ * @license GPL2 or any later version
+ */
+namespace exTpl;
+
+class Scanner
+{
+    private array $tokens;
+    private mixed $token_type;
+    private mixed $token_value;
+
+    /**
+     * Initializes a new Scanner instance for the given text.
+     *
+     * @param string $text string to parse
+     */
+    public function __construct(string $text)
+    {
+        $this->tokens = token_get_all('<?php ' . $text);
+    }
+
+    /**
+     * Advances the scanner to the next token and returns its token type.
+     * The valid token types are those defined for token_get_all() in the
+     * PHP documentation. Returns false when the end of input is reached.
+     */
+    public function nextToken(): mixed
+    {
+        do {
+            $token = next($this->tokens);
+            $key   = key($this->tokens);
+
+            // FIXME this workaround should be dropped
+            while (
+                $token && $token[0] === T_STRING
+                && isset($this->tokens[$key + 2])
+                && $this->tokens[++$key] === '-'
+                && $this->tokens[++$key][0] === T_STRING
+            ) {
+                $token[1] .= '-' . $this->tokens[$key][1];
+                next($this->tokens);
+                next($this->tokens);
+            }
+        } while (is_array($token) && $token[0] === T_WHITESPACE);
+
+        if (is_string($token) || $token === false) {
+            $this->token_type  = $token;
+            $this->token_value = null;
+        } else {
+            $this->token_type = $token[0];
+
+            $this->token_value = match ($token[0]) {
+                T_CONSTANT_ENCAPSED_STRING => stripcslashes(substr($token[1], 1, -1)),
+                T_DNUMBER => (double) $token[1],
+                T_LNUMBER => (int) $token[1],
+                default => $token[1],
+            };
+        }
+
+        return $this->token_type;
+    }
+
+    /**
+     * Returns the current token type. The valid token types are
+     * those defined for token_get_all() in the PHP documentation.
+     */
+    public function tokenType(): mixed
+    {
+        return $this->token_type;
+    }
+
+    /**
+     * Returns the current token value if the token type supports
+     * a value (T_STRING, T_LNUMBER etc.). Returns null otherwise.
+     */
+    public function tokenValue(): mixed
+    {
+        return $this->token_value;
+    }
+}
diff --git a/lib/exTpl/SymbolExpression.php b/lib/exTpl/SymbolExpression.php
new file mode 100644
index 0000000..178a51f
--- /dev/null
+++ b/lib/exTpl/SymbolExpression.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * SymbolExpression represents a symbol (template variable).
+ */
+class SymbolExpression implements Expression
+{
+    protected string $name;
+
+    /**
+     * Initializes a new Expression instance.
+     *
+     * @param string $name      symbol name
+     */
+    public function __construct(string $name)
+    {
+        $this->name = $name;
+    }
+
+    /**
+     * Returns the name of this symbol.
+     */
+    public function name(): string
+    {
+        return $this->name;
+    }
+
+    /**
+     * Returns the value of this expression.
+     *
+     * @param Context $context  symbol table
+     */
+    public function value(Context $context): mixed
+    {
+        return $context->lookup($this->name);
+    }
+}
diff --git a/lib/exTpl/Template.php b/lib/exTpl/Template.php
new file mode 100644
index 0000000..274e115
--- /dev/null
+++ b/lib/exTpl/Template.php
@@ -0,0 +1,547 @@
+<?php
+/*
+ * Template.php - expression template parser
+ *
+ * Copyright (c) 2013  Elmar Ludwig
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ */
+
+namespace exTpl;
+
+use Closure;
+use InvalidArgumentException;
+
+
+/**
+ * The Template class is the only externally visible API of this
+ * template implementation. It can be used to create and render
+ * template objects.
+ */
+class Template
+{
+    private static string $tag_start = '{';
+    private static string $tag_end   = '}';
+    private Closure|string|null $escape = null;
+    private array $functions;
+    private ArrayNode $template;
+
+    /**
+     * Sets the delimiter strings used for the template tags, the
+     * default delimiters are: $tag_start = '{', $tag_end = '}'.
+     *
+     * @param string $tag_start tag start marker
+     * @param string $tag_end tag end marker
+     */
+    public static function setTagMarkers(string $tag_start, string $tag_end): void
+    {
+        self::$tag_start = $tag_start;
+        self::$tag_end   = $tag_end;
+    }
+
+    /**
+     * Initializes a new Template instance from the given string.
+     *
+     * @param string $string template text
+     *
+     * @throws TemplateParserException
+     */
+    public function __construct(string $string)
+    {
+        $this->template  = new ArrayNode();
+        $this->functions = [
+            'count'  => fn($a) => count($a),
+            'strlen' => fn($a) => mb_strlen($a),
+        ];
+        self::parseTemplate($this->template, $string, 0);
+    }
+
+    /**
+     * Enables or disables automatic escaping for template values.
+     * Currently supported strategies: NULL, 'html', 'json', 'xml'
+     *
+     * @param callable|string|null $escape escape strategy or callback
+     */
+    public function autoescape(callable|string|null $escape): void
+    {
+        if ($escape === 'html' || $escape === 'xml') {
+            $this->escape = 'htmlspecialchars';
+        } else if ($escape === 'json') {
+            $this->escape = 'json_encode';
+        } else if (is_callable($escape)) {
+            $this->escape = $escape;
+        } else if ($escape === null) {
+            $this->escape = null;
+        } else {
+            throw new InvalidArgumentException("invalid escape strategy: $escape");
+        }
+    }
+
+    /**
+     * Renders the template to a string using the given array of
+     * bindings to resolve symbol references inside the template.
+     *
+     * @param array $bindings symbol table
+     *
+     * @return string   string representation of the template
+     */
+    public function render(array $bindings): string
+    {
+        $context = new Context($bindings + $this->functions);
+        $context->autoescape($this->escape);
+
+        return $this->template->render($context);
+    }
+
+    /**
+     * Skips tokens until the end of the current tag is reached.
+     *
+     * @param string $string template text
+     * @param int $pos offset in string
+     *
+     * @return int new offset in the string
+     */
+    private static function skipTokens(string $string, int $pos): int
+    {
+        for ($len = strlen($string); $pos < $len && substr_compare($string, self::$tag_end, $pos, strlen(self::$tag_end)); ++$pos) {
+            $chr = $string[$pos];
+            if ($chr === '"' || $chr === "'") {
+                while (++$pos < $len && $string[$pos] !== $chr) {
+                    if ($string[$pos] === '\\') {
+                        ++$pos;
+                    }
+                }
+            }
+        }
+
+        return $pos;
+    }
+
+    /**
+     * Parses a template string into a template node tree, starting
+     * at the specified offset. All created nodes are added to the
+     * given sequence node.
+     *
+     * @param ArrayNode $node   template node to build
+     * @param string    $string string to parse
+     * @param int       $pos    offset in string
+     *
+     * @return int      new offset in the string
+     * @throws TemplateParserException
+     */
+    private static function parseTemplate(ArrayNode $node, string $string, int $pos): int
+    {
+        $len = strlen($string);
+
+        while ($pos < $len) {
+            $next_pos = strpos($string, self::$tag_start, $pos);
+
+            if ($next_pos === false) {
+                $child = new TextNode(substr($string, $pos));
+                $node->addChild($child);
+                break;
+            }
+
+            if ($next_pos > $pos) {
+                $child = new TextNode(substr($string, $pos, $next_pos - $pos));
+                $node->addChild($child);
+            }
+
+            $pos      = $next_pos + strlen(self::$tag_start);
+            $next_pos = self::skipTokens($string, $pos);
+            $scanner  = new Scanner(substr($string, $pos, $next_pos - $pos));
+            $pos      = $next_pos + strlen(self::$tag_end);
+
+            switch ($scanner->nextToken()) {
+                case T_FOREACH:
+                    $scanner->nextToken();
+                    $expr     = self::parseExpr($scanner);
+                    $key_name = 'index';
+                    $val_name = 'this';
+
+                    if ($scanner->tokenType() === T_AS) {
+                        $scanner->nextToken();
+
+                        if ($scanner->tokenType() !== T_STRING) {
+                            throw new TemplateParserException('symbol expected', $scanner);
+                        }
+
+                        $val_name = $scanner->tokenValue();
+                        $scanner->nextToken();
+
+                        if ($scanner->tokenType() === T_DOUBLE_ARROW) {
+                            $scanner->nextToken();
+
+                            if ($scanner->tokenType() !== T_STRING) {
+                                throw new TemplateParserException('symbol expected', $scanner);
+                            }
+
+                            $key_name = $val_name;
+                            $val_name = $scanner->tokenValue();
+                            $scanner->nextToken();
+                        }
+                    }
+
+                    $child = new IteratorNode($expr, $key_name, $val_name);
+                    $pos   = self::parseTemplate($child, $string, $pos);
+                    $node->addChild($child);
+                    break;
+                case T_ENDIF:
+                case T_ENDFOREACH:
+                    return $pos;
+                case T_IF:
+                    $scanner->nextToken();
+                    $child = new ConditionNode(self::parseExpr($scanner));
+                    $pos   = self::parseTemplate($child, $string, $pos);
+                    $node->addChild($child);
+                    break;
+                case T_ELSEIF:
+                    $scanner->nextToken();
+                    $child = new ConditionNode(self::parseExpr($scanner));
+                    $node->addElse();
+                    $node->addChild($child);
+                    return self::parseTemplate($child, $string, $pos);
+                case T_ELSE:
+                    $scanner->nextToken();
+                    $node->addElse();
+                    break;
+                default:
+                    $child = new ExpressionNode(self::parseExpr($scanner));
+                    $node->addChild($child);
+            }
+
+            if ($scanner->tokenType() !== false) {
+                throw new TemplateParserException('syntax error', $scanner);
+            }
+        }
+
+        return $pos;
+    }
+
+    /**
+     * value: NUMBER | STRING | SYMBOL | '(' expr ')'
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseValue(Scanner $scanner): mixed
+    {
+        switch ($scanner->tokenType()) {
+            case T_CONSTANT_ENCAPSED_STRING:
+            case T_DNUMBER:
+            case T_LNUMBER:
+                $result = new ConstantExpression($scanner->tokenValue());
+                break;
+            case T_STRING:
+                $result = new SymbolExpression($scanner->tokenValue());
+                break;
+            case '(':
+                $scanner->nextToken();
+                $result = self::parseExpr($scanner);
+
+                if ($scanner->tokenType() !== ')') {
+                    throw new TemplateParserException('missing ")"', $scanner);
+                }
+                break;
+            default:
+                throw new TemplateParserException('syntax error', $scanner);
+        }
+
+        $scanner->nextToken();
+        return $result;
+    }
+
+    /**
+     * function: value | function '(' ')' | function '(' expr { ',' expr } ')'
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseFunction(Scanner $scanner): mixed
+    {
+        $result = self::parseValue($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === '(') {
+            $scanner->nextToken();
+            $arguments = [];
+
+            if ($scanner->tokenType() !== ')') {
+                $arguments[] = self::parseExpr($scanner);
+
+                while ($scanner->tokenType() === ',') {
+                    $scanner->nextToken();
+                    $arguments[] = self::parseExpr($scanner);
+                }
+
+                if ($scanner->tokenType() !== ')') {
+                    throw new TemplateParserException('missing ")"', $scanner);
+                }
+            }
+
+            $scanner->nextToken();
+            $result = new FunctionExpression($result, $arguments);
+            $type   = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * index: function | index '[' expr ']' | index '.' SYMBOL
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseIndex(Scanner $scanner): mixed
+    {
+        $result = self::parseFunction($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === '[' || $type === '.') {
+            $scanner->nextToken();
+
+            if ($type === '[') {
+                $expr = self::parseExpr($scanner);
+
+                if ($scanner->tokenType() !== ']') {
+                    throw new TemplateParserException('missing "]"', $scanner);
+                }
+            } else if ($scanner->tokenType() === T_STRING) {
+                $expr = new ConstantExpression($scanner->tokenValue());
+            } else {
+                throw new TemplateParserException('symbol expected', $scanner);
+            }
+
+            $scanner->nextToken();
+            $result = new IndexExpression($result, $expr, $type);
+            $type = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * filter: index | filter '|' SYMBOL | filter '|' SYMBOL '(' expr { ',' expr } ')'
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseFilter(Scanner $scanner): mixed
+    {
+        $result = self::parseIndex($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === '|') {
+            $scanner->nextToken();
+
+            if ($scanner->tokenType() !== T_STRING) {
+                throw new TemplateParserException('symbol expected', $scanner);
+            }
+
+            $arguments = [$result];
+            $symbol    = new SymbolExpression($scanner->tokenValue());
+            $scanner->nextToken();
+
+            if ($scanner->tokenType() === '(') {
+                $scanner->nextToken();
+
+                if ($scanner->tokenType() !== ')') {
+                    $arguments[] = self::parseExpr($scanner);
+
+                    while ($scanner->tokenType() === ',') {
+                        $scanner->nextToken();
+                        $arguments[] = self::parseExpr($scanner);
+                    }
+
+                    if ($scanner->tokenType() !== ')') {
+                        throw new TemplateParserException('missing ")"', $scanner);
+                    }
+                }
+
+                $scanner->nextToken();
+            }
+
+            if ($symbol->name() === 'raw') {
+                $result = new RawExpression($result);
+            } else {
+                $result = new FunctionExpression($symbol, $arguments);
+            }
+
+            $type = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * sign: '!' sign | '+' sign | '-' sign | filter
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseSign(Scanner $scanner): mixed
+    {
+        switch ($scanner->tokenType()) {
+            case '!':
+                $scanner->nextToken();
+                $result = new NotExpression(self::parseSign($scanner));
+                break;
+            case '+':
+                $scanner->nextToken();
+                $result = self::parseSign($scanner);
+                break;
+            case '-':
+                $scanner->nextToken();
+                $result = new MinusExpression(self::parseSign($scanner));
+                break;
+            default:
+                $result = self::parseFilter($scanner);
+        }
+
+        return $result;
+    }
+
+    /**
+     * product: sign | product '*' sign | product '/' sign | product '%' sign
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseProduct(Scanner $scanner): mixed
+    {
+        $result = self::parseSign($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === '*' || $type === '/' || $type === '%') {
+            $scanner->nextToken();
+            $result = new ArithExpression($result, self::parseSign($scanner), $type);
+            $type   = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * sum: product | sum '+' product | sum '-' product | sum '~' product
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseSum(Scanner $scanner): mixed
+    {
+        $result = self::parseProduct($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === '+' || $type === '-' || $type === '~') {
+            $scanner->nextToken();
+            $result = new ArithExpression($result, self::parseProduct($scanner), $type);
+            $type   = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * lt_gt: sum | lt_gt '<' concat | lt_gt IS_SMALLER_OR_EQUAL concat
+     *            | lt_gt '>' concat | lt_gt IS_GREATER_OR_EQUAL concat
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseLtGt(Scanner $scanner): mixed
+    {
+        $result = self::parseSum($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === '<' || $type === T_IS_SMALLER_OR_EQUAL ||
+            $type === '>' || $type === T_IS_GREATER_OR_EQUAL) {
+            $scanner->nextToken();
+            $result = new BooleanExpression($result, self::parseSum($scanner), $type);
+            $type   = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * cmp: lt_gt | cmp IS_EQUAL lt_gt | cmp IS_NOT_EQUAL lt_gt
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseCmp(Scanner $scanner): mixed
+    {
+        $result = self::parseLtGt($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === T_IS_EQUAL || $type === T_IS_NOT_EQUAL) {
+            $scanner->nextToken();
+            $result = new BooleanExpression($result, self::parseLtGt($scanner), $type);
+            $type   = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * and: cmp | and BOOLEAN_AND cmp
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseAnd(Scanner $scanner): mixed
+    {
+        $result = self::parseCmp($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === T_BOOLEAN_AND) {
+            $scanner->nextToken();
+            $result = new BooleanExpression($result, self::parseCmp($scanner), $type);
+            $type   = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * or: and | or BOOLEAN_OR and
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseOr(Scanner $scanner): mixed
+    {
+        $result = self::parseAnd($scanner);
+        $type   = $scanner->tokenType();
+
+        while ($type === T_BOOLEAN_OR) {
+            $scanner->nextToken();
+            $result = new BooleanExpression($result, self::parseAnd($scanner), $type);
+            $type   = $scanner->tokenType();
+        }
+
+        return $result;
+    }
+
+    /**
+     * expr: or | or '?' expr ':' expr | or '?' ':' expr
+     *
+     * @throws TemplateParserException
+     */
+    private static function parseExpr(Scanner $scanner): mixed
+    {
+        $result = self::parseOr($scanner);
+
+        if ($scanner->tokenType() === '?') {
+            $scanner->nextToken();
+
+            if ($scanner->tokenType() !== ':') {
+                $expr = self::parseExpr($scanner);
+            } else {
+                $expr = $result;
+            }
+
+            if ($scanner->tokenType() !== ':') {
+                throw new TemplateParserException('missing ":"', $scanner);
+            }
+
+            $scanner->nextToken();
+            $result = new ConditionExpression($result, $expr, self::parseExpr($scanner));
+        }
+
+        return $result;
+    }
+}
diff --git a/lib/exTpl/TemplateParserException.php b/lib/exTpl/TemplateParserException.php
new file mode 100644
index 0000000..2c7abf8
--- /dev/null
+++ b/lib/exTpl/TemplateParserException.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace exTpl;
+
+use Exception;
+
+/**
+ * Exception class used to report template parse errors.
+ */
+class TemplateParserException extends Exception
+{
+    public function __construct(string $message, Scanner $scanner)
+    {
+        $type  = $scanner->tokenType();
+        $value = is_int($type) ? $scanner->tokenValue() : $type;
+
+        return parent::__construct("$message at \"$value\"");
+    }
+}
diff --git a/lib/exTpl/TextNode.php b/lib/exTpl/TextNode.php
new file mode 100644
index 0000000..053cafc
--- /dev/null
+++ b/lib/exTpl/TextNode.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * TextNode represents a verbatim text segment.
+ */
+class TextNode implements Node
+{
+    protected string $text;
+
+    /**
+     * Initializes a new Node instance with the given text.
+     *
+     * @param string $text verbatim text
+     */
+    public function __construct(string $text)
+    {
+        $this->text = $text;
+    }
+
+    /**
+     * Returns a string representation of this node.
+     *
+     * @param Context $context symbol table
+     */
+    public function render(Context $context): string
+    {
+        return $this->text;
+    }
+}
diff --git a/lib/exTpl/UnaryExpression.php b/lib/exTpl/UnaryExpression.php
new file mode 100644
index 0000000..9979311
--- /dev/null
+++ b/lib/exTpl/UnaryExpression.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace exTpl;
+
+/**
+ * UnaryExpression represents a unary operator.
+ */
+abstract class UnaryExpression implements Expression
+{
+    protected Expression $expr;
+
+    /**
+     * Initializes a new Expression instance.
+     *
+     * @param Expression $expr  expression object
+     */
+    public function __construct(Expression $expr)
+    {
+        $this->expr = $expr;
+    }
+}