# Simple Scripting Language

A functional programming language with immutable variables, first-class functions, and pattern matching.

## Features

- **Immutable Variables**: Variables cannot be reassigned
- **First-Class Functions**: Functions can be passed as arguments and stored in data structures
- **Lexical Scoping**: Functions create their own scope
- **Pattern Matching**: Case expressions with wildcard support
- **Table Literals**: Lua-style tables with both array-like and key-value entries
- **Standard Library**: Built-in higher-order functions (`map`, `compose`, `pipe`, `apply`, `filter`, `reduce`, `fold`, `curry`)
- **IO Operations**: Built-in input/output operations (`..in`, `..out`, `..assert`)
- **Floating Point Arithmetic**: Full support for decimal numbers
- **Unary Minus**: Support for negative numbers (e.g., `-1`, `-3.14`)

## Syntax

### Basic Operations
```
/* Arithmetic */
x : 5 + 3;
y : 10 - 2;
z : 4 * 3;
w : 15 / 3;
neg : -5;  /* Unary minus */

/* Comparisons */
result : x > y;
equal : a = b;
not_equal : a != b;

/* Logical */
and_result : true and false;
or_result : true or false;
```

### Variables and Functions
```
/* Immutable variables */
x : 42;
y : "hello";

/* Function definition */
f : x -> x * 2;

/* Function call */
result : f 5;
```

### Tables
```
/* Table literal */
table : {1, 2, 3, key: "value"};

/* Table access */
first : table[1];
value : table.key;
nested : table.key.subkey;
```

### Pattern Matching
```
/* Case expression */
result : case x of
    1 : "one"
    2 : "two"
    _ : "other";
```

### IO Operations
```
/* Output */
..out "Hello, World!";

/* Input */
name : ..in;

/* Assertion */
..assert x = 5;
```

### Standard Library
```
/* Map */
double : x -> x * 2;
squared : map @double 5;

/* Filter */
isPositive : x -> x > 0;
filtered : filter @isPositive 5;

/* Compose */
f : x -> x + 1;
g : x -> x * 2;
h : compose @f @g;
result : h 5;  /* (5 * 2) + 1 = 11 */
```

## Usage

### Running Scripts
```bash
node lang.js script.txt
```

### Testing
The project uses a structured testing approach with unit and integration tests:

#### Unit Tests
Located in `tests/` directory, each focusing on a specific language feature:
- `01_lexer_basic.txt` - Basic lexer functionality
- `02_arithmetic_operations.txt` - Arithmetic operations
- `03_comparison_operators.txt` - Comparison operators
- `04_logical_operators.txt` - Logical operators
- `05_io_operations.txt` - IO operations
- `06_function_definitions.txt` - Function definitions
- `07_case_expressions.txt` - Case expressions and pattern matching
- `08_first_class_functions.txt` - First-class function features
- `09_tables.txt` - Table literals and access
- `10_standard_library.txt` - Standard library functions

#### Integration Tests
Test combinations of multiple features:
- `integration_01_basic_features.txt` - Basic feature combinations
- `integration_02_pattern_matching.txt` - Pattern matching with other features
- `integration_03_functional_programming.txt` - Functional programming patterns

#### Running Tests
```bash
# Run all tests
./run_tests.sh

# Run individual tests
node lang.js tests/01_lexer_basic.txt
node lang.js tests/integration_01_basic_features.txt
```

## Implementation Details

### Architecture
- **Lexer**: Tokenizes input into tokens (numbers, identifiers, operators, etc.)
- **Parser**: Builds Abstract Syntax Tree (AST) from tokens
- **Interpreter**: Executes AST with scope management

### Key Components
- **Token Types**: Supports all basic operators, literals, and special tokens
- **AST Nodes**: Expression, statement, and declaration nodes
- **Scope Management**: Lexical scoping with proper variable resolution
- **Error Handling**: Comprehensive error reporting for parsing and execution

## Recent Fixes

### ✅ Parser Ambiguity with Unary Minus Arguments (Latest Fix)
- **Issue**: `filter @isPositive -3` was incorrectly parsed as binary operation instead of function call with unary minus argument
- **Root Cause**: Parser treating `FunctionReference MINUS` as binary minus operation
- **Solution**: Added special case in `parseExpression()` to handle `FunctionReference MINUS` pattern
- **Status**: ✅ Resolved - Standard library functions now work with negative arguments

### ✅ Unary Minus Operator
- **Issue**: Stack overflow when parsing negative numbers (e.g., `-1`)
- **Root Cause**: Parser lacked specific handling for unary minus operator
- **Solution**: Added `UnaryMinusExpression` parsing and evaluation
- **Status**: ✅ Resolved - All tests passing

### ✅ IO Operation Parsing
- **Issue**: IO operations not parsed correctly at top level
- **Solution**: Moved IO parsing to proper precedence level
- **Status**: ✅ Resolved

### ✅ Decimal Number Support
- **Issue**: Decimal numbers not handled correctly
- **Solution**: Updated lexer and interpreter to use `parseFloat()`
- **Status**: ✅ Resolved

## Known Issues

### 🔄 Logical Operator Precedence
- **Issue**: Logical operators (`and`, `or`, `xor`) have incorrect precedence relative to function calls
- **Example**: `isEven 10 and isPositive 5` is parsed as `isEven(10 and isPositive(5))` instead of `(isEven 10) and (isPositive 5)`
- **Impact**: Complex expressions with logical operators may not evaluate correctly
- **Status**: 🔄 In Progress - Working on proper operator precedence hierarchy
- **Workaround**: Use parentheses to explicitly group expressions: `(isEven 10) and (isPositive 5)`

### 🔄 Parentheses Parsing with Logical Operators
- **Issue**: Some expressions with logical operators inside parentheses fail to parse
- **Example**: `add (multiply 3 4) (isEven 10 and isPositive 5)` may fail with parsing errors
- **Status**: 🔄 In Progress - Related to logical operator precedence issue

## Development

### File Structure
```
.
├── lang.js              # Main implementation
├── test.txt             # Comprehensive test file
├── tests/               # Unit and integration tests
│   ├── 01_lexer_basic.txt
│   ├── 02_arithmetic_operations.txt
│   ├── ...
│   ├── integration_01_basic_features.txt
│   ├── integration_02_pattern_matching.txt
│   └── integration_03_functional_programming.txt
├── run_tests.sh         # Test runner script
├── FIXME.md             # Issues and fixes documentation
└── README.md            # This file
```

### Debugging
Enable debug mode by setting `DEBUG=true`:
```bash
DEBUG=true node lang.js script.txt
```

## Contributing

1. Create focused unit tests for new features
2. Add integration tests for feature combinations
3. Update documentation
4. Run the full test suite before submitting changes