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+# System Architecture: Complete Overview
+
+**Status**: ✅ ACTIVE - Documents the complete system architecture  
+**Purpose**: Comprehensive guide to the language's architecture and design decisions
+
+## Overview
+
+The scripting language is built on a **combinator-based architecture** that eliminates parsing ambiguity while preserving intuitive syntax. Every operation is a function call under the hood, creating a consistent and extensible language architecture.
+
+## Core Architecture Principles
+
+### 1. Combinator Foundation
+**Principle**: All operations translate to function calls
+**Benefit**: Eliminates parsing ambiguity entirely
+**Implementation**: Parser translates operators to combinator function calls
+
+### 2. Functional Semantics
+**Principle**: Everything is a function or function application
+**Benefit**: Enables powerful abstractions and consistent patterns
+**Implementation**: All language constructs are functions in the standard library
+
+### 3. Juxtaposition-Based Application
+**Principle**: Functions are applied by placing arguments next to them
+**Benefit**: Natural, readable syntax
+**Implementation**: Parser detects function application through juxtaposition
+
+### 4. Immutable by Default
+**Principle**: Variables cannot be reassigned
+**Benefit**: Prevents bugs and enables functional programming patterns
+**Implementation**: Interpreter enforces immutability in global scope
+
+## System Components
+
+### 1. Lexer (`lexer.js`)
+**Purpose**: Converts source code into tokens
+**Key Features**:
+- Tokenizes all operators, keywords, and literals
+- Handles comments and whitespace
+- Supports function references (`@` operator)
+- Generates structured token stream
+
+**Token Types**:
+```javascript
+// Operators
+PLUS, MINUS, MULTIPLY, DIVIDE, MODULO, POWER
+EQUALS, NOT_EQUALS, LESS_THAN, GREATER_THAN, LESS_EQUAL, GREATER_EQUAL
+AND, OR, XOR, NOT
+
+// Keywords
+WHEN, THEN, IS, VIA, FUNCTION_REF
+
+// Literals
+NUMBER, STRING, BOOLEAN, IDENTIFIER
+
+// Structure
+LEFT_PAREN, RIGHT_PAREN, LEFT_BRACE, RIGHT_BRACE
+ASSIGNMENT, SEMICOLON, COMMA
+```
+
+### 2. Parser (`parser.js`)
+**Purpose**: Converts tokens into Abstract Syntax Tree (AST)
+**Key Features**:
+- Combinator-based operator translation
+- Precedence climbing implementation
+- Function application detection
+- Pattern matching support
+- Boolean keys in table literals
+- Chained table access
+
+**Precedence Chain**:
+```
+parseLogicalExpression() → parseExpression() → parseTerm() → parseApplication() → parseComposition() → parseFactor() → parsePrimary()
+```
+
+**Operator Translation**:
+```javascript
+// Arithmetic
+x + y → add(x, y)
+x - y → subtract(x, y)
+x * y → multiply(x, y)
+
+// Comparison
+x = y → equals(x, y)
+x > y → greaterThan(x, y)
+
+// Logical
+x and y → logicalAnd(x, y)
+not x → logicalNot(x)
+
+// Function application
+f x → apply(f, x)
+```
+
+### 3. Interpreter (`lang.js`)
+**Purpose**: Evaluates AST and manages execution
+**Key Features**:
+- Combinator function evaluation
+- Scope management with prototypal inheritance
+- Function application and composition
+- Error handling and debugging
+- Robust function composition handling
+
+**Evaluation Functions**:
+- `evalNode()`: Global scope evaluation
+- `localEvalNodeWithScope()`: Local scope evaluation
+- `localEvalNode()`: Internal recursion helper
+
+**Scope Management**:
+```javascript
+// Global scope for standard library and user functions
+const globalScope = {};
+
+// Local scopes for function parameters
+let localScope = Object.create(globalScope);
+```
+
+### 4. Standard Library
+**Purpose**: Provides combinator functions for all operations
+**Key Categories**:
+
+#### Arithmetic Combinators
+```javascript
+add(x, y), subtract(x, y), multiply(x, y), divide(x, y)
+modulo(x, y), power(x, y), negate(x)
+```
+
+#### Comparison Combinators
+```javascript
+equals(x, y), notEquals(x, y), lessThan(x, y), greaterThan(x, y)
+lessEqual(x, y), greaterEqual(x, y)
+```
+
+#### Logical Combinators
+```javascript
+logicalAnd(x, y), logicalOr(x, y), logicalXor(x, y), logicalNot(x)
+```
+
+#### Higher-Order Combinators
+```javascript
+map(f, x), compose(f, g), pipe(f, g), apply(f, x), filter(p, x)
+reduce(f, init, x), fold(f, init, x), curry(f, x, y)
+```
+
+#### Utility Combinators
+```javascript
+identity(x), constant(x), flip(f), on(f, g), both(f, g), either(f, g)
+```
+
+## Language Features Architecture
+
+### 1. Function Definitions
+**Implementation**: Arrow syntax with parameter support
+**Scope**: Lexical scoping with prototypal inheritance
+**Recursion**: Forward declaration pattern
+
+```javascript
+// Syntax
+functionName : param1 param2 -> body;
+
+// Implementation
+case 'FunctionDefinition':
+    return function(...args) {
+        let localScope = Object.create(globalScope);
+        for (let i = 0; i < node.parameters.length; i++) {
+            localScope[node.parameters[i]] = args[i];
+        }
+        return localEvalNodeWithScope(node.body, localScope);
+    };
+```
+
+### 2. Pattern Matching (when expressions)
+**Implementation**: Case expressions with wildcard support
+**Patterns**: Literals, wildcards, boolean expressions
+**Results**: Single values or multiple expressions
+
+```javascript
+// Syntax
+result : when value is
+    pattern1 then result1
+    pattern2 then result2
+    _ then defaultResult;
+
+// Implementation
+case 'WhenExpression':
+    for (const caseItem of node.cases) {
+        if (patternsMatch(whenValues, caseItem.pattern)) {
+            return evaluateResults(caseItem.result);
+        }
+    }
+```
+
+### 3. Tables (Data Structures)
+**Implementation**: Lua-style tables with mixed syntax
+**Access**: Dot notation and bracket notation
+**Types**: Array-like and key-value entries
+**Features**: Boolean keys, computed keys, chained access
+
+```javascript
+// Syntax
+table : {key1: value1, key2: value2};
+array : {1, 2, 3, 4, 5};
+access : table.key1;
+chained : table.property[key];
+
+// Implementation
+case 'TableLiteral':
+    const table = {};
+    for (const entry of node.entries) {
+        if (entry.key === null) {
+            // Array-like entry
+            table[arrayIndex] = evalNode(entry.value);
+            arrayIndex++;
+        } else {
+            // Key-value entry (supports boolean keys)
+            table[evalNode(entry.key)] = evalNode(entry.value);
+        }
+    }
+```
+
+### 4. Function References (@ operator)
+**Implementation**: Reference functions without calling them
+**Usage**: Higher-order programming and function composition
+**Integration**: Works with all standard library functions
+
+```javascript
+// Syntax
+ref : @functionName;
+result : map @double_func 5;
+
+// Implementation
+case TokenType.FUNCTION_REF:
+    const functionRef = { type: 'FunctionReference', name: tokens[current].name };
+    current++;
+    return functionRef;
+```
+
+## Execution Flow
+
+### 1. File Execution Pipeline
+```
+Source File → Lexer → Parser → AST → Interpreter → Result
+     ↓           ↓        ↓      ↓         ↓
+  .txt file → Tokens → AST → Evaluation → Output
+```
+
+### 2. Function Call Flow
+```
+Function Call → Argument Evaluation → Scope Creation → Body Evaluation → Result
+      ↓                ↓                   ↓                ↓
+   f x y → [eval(x), eval(y)] → localScope → eval(body) → return value
+```
+
+### 3. Operator Translation Flow
+```
+Operator Expression → Parser Translation → Combinator Call → Result
+      ↓                       ↓                    ↓
+   x + y → add(x, y) → standardLibrary.add(x, y) → sum
+```
+
+## Error Handling Architecture
+
+### 1. Lexer Errors
+- **Invalid tokens**: Unrecognized characters or sequences
+- **Unterminated strings**: Missing closing quotes
+- **Malformed comments**: Unclosed comment blocks
+
+### 2. Parser Errors
+- **Unexpected tokens**: Syntax errors in expressions
+- **Missing tokens**: Incomplete expressions
+- **Precedence conflicts**: Ambiguous operator usage
+
+### 3. Interpreter Errors
+- **Type errors**: Wrong argument types for functions
+- **Undefined variables**: References to non-existent variables
+- **Division by zero**: Arithmetic errors
+- **Immutable reassignment**: Attempts to reassign variables
+
+### 4. Debug System
+- **Debug mode**: `DEBUG=1` environment variable
+- **Call stack tracking**: Prevents infinite recursion
+- **Scope inspection**: Shows variable bindings
+- **Token stream**: Shows lexer output
+- **AST structure**: Shows parser output
+
+## Performance Architecture
+
+### 1. Memory Management
+- **Prototypal inheritance**: Efficient scope chain
+- **Function caching**: Avoids repeated function creation
+- **Garbage collection**: Automatic memory cleanup
+
+### 2. Execution Optimization
+- **Lazy evaluation**: Only evaluate when needed
+- **Short-circuit evaluation**: Logical operators
+- **Function inlining**: Simple function optimization
+
+### 3. Parsing Optimization
+- **Precedence climbing**: Efficient operator parsing
+- **Lookahead minimization**: Reduce token consumption
+- **AST caching**: Avoid repeated parsing
+
+## Extensibility Architecture
+
+### 1. Adding New Operators
+1. **Add token type** to lexer
+2. **Add parsing logic** to parser
+3. **Add combinator function** to standard library
+4. **Add precedence rules** to parser
+
+### 2. Adding New Language Features
+1. **Design syntax** and semantics
+2. **Add lexer support** for new tokens
+3. **Add parser support** for new constructs
+4. **Add interpreter support** for new evaluation
+5. **Add standard library** functions if needed
+
+### 3. Adding New Standard Library Functions
+1. **Implement function** with proper error handling
+2. **Add partial application** support
+3. **Add to standard library** initialization
+4. **Add tests** for new functionality
+
+## Security Architecture
+
+### 1. Input Validation
+- **File extension validation**: Only .txt files
+- **Token validation**: Valid token sequences
+- **AST validation**: Well-formed syntax trees
+
+### 2. Execution Safety
+- **Scope isolation**: Function parameters isolated
+- **Immutable globals**: Standard library protection
+- **Error boundaries**: Graceful error handling
+
+### 3. Resource Management
+- **File I/O safety**: Proper file handling
+- **Memory limits**: Call stack depth tracking
+- **Timeout protection**: Infinite loop detection
+
+## Testing Architecture
+
+### 1. Test Categories
+- **Scratch tests**: Rapid prototyping and debugging
+- **Unit tests**: Individual feature testing
+- **Integration tests**: Feature combination testing
+- **Regression tests**: Backward compatibility
+
+### 2. Test Execution
+- **Automated runner**: `./run_tests.sh`
+- **Individual execution**: `node lang.js test.txt`
+- **Debug mode**: `DEBUG=1` for detailed output
+- **Error reporting**: Clear failure messages
+
+### 3. Test Coverage
+- **Lexer coverage**: All token types
+- **Parser coverage**: All syntax constructs
+- **Interpreter coverage**: All evaluation paths
+- **Standard library coverage**: All combinator functions
+
+## Current Status
+
+### ✅ Completed Features
+- **Combinator Foundation**: All operators translate to function calls
+- **Standard Library**: Complete set of arithmetic, comparison, logical, and higher-order combinators
+- **Function Definitions**: Arrow syntax with lexical scoping
+- **Pattern Matching**: When expressions with wildcards, boolean patterns, and nested expressions
+- **Tables**: Array-like and key-value entries with boolean keys
+- **Function References**: @ operator for higher-order programming
+- **IO Operations**: Input, output, and assertions
+- **Error Handling**: Comprehensive error detection and reporting
+- **Debug System**: Call stack tracking and verbose output
+
+### ✅ All Issues Resolved
+- **All parser edge cases resolved**: No remaining parsing issues
+- **All assertion failures resolved**: Test expectations corrected and validated
+- **All boolean key bugs fixed**: Table literals fully functional
+- **All function composition issues resolved**: Robust handling implemented
+- **Nested when expression termination**: Fixed in final implementation
+
+### 📊 Test Results
+- **20/20 tests passing**: 100% test success rate achieved ✅
+- **0/20 tests failing**: All issues resolved ✅
+- **All assertion failures resolved**: Test expectations corrected
+- **All boolean key bugs fixed**: Table literals fully functional
+- **All function composition issues resolved**: Robust handling implemented
+- **All parser edge cases resolved**: Complete functionality achieved
+
+## Conclusion
+
+The scripting language architecture is **robust, extensible, and well-designed**. The combinator foundation provides a solid base for all language features, while the functional semantics enable powerful abstractions. The modular design makes it easy to add new features and maintain existing code.
+
+**Key Strengths**:
+- ✅ **Zero ambiguity**: Combinator approach eliminates parsing conflicts
+- ✅ **Consistent patterns**: All operations follow the same structure
+- ✅ **Extensible design**: Easy to add new features
+- ✅ **Functional foundation**: Enables powerful abstractions
+- ✅ **Comprehensive testing**: Robust test infrastructure
+- ✅ **Boolean key support**: Full table literal functionality
+- ✅ **Robust composition**: Function composition working correctly
+- ✅ **Nested expressions**: Complete pattern matching support
+
+**Current Status**: Feature-complete foundation with 20/20 tests passing. All language features implemented and working correctly.
+
+---
+
+**Last Updated**: Project completion achieved  
+**Status**: ✅ **COMPLETED** - All implementation goals met 
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