gladlang 0.1.2

The GladLang Interpreter

GladLang

GladLang is a dynamic, interpreted, object-oriented programming language. This is a full interpreter built from scratch in Python, complete with a lexer, parser, and runtime environment. It supports modern programming features like closures, classes, inheritance, and robust error handling.

This is the full overview of the GladLang language, its features, and how to run the interpreter.

Table of Contents

• About The Language
• Key Features
• Getting Started
  • 1. Installation
  • 2. Usage
  • 3. Running Without Installation (Source)
  • 4. Building the Executable
• Language Tour (Syntax Reference)
  • 1. Comments
  • 2. Variables and Data Types
    • Variables
    • Numbers
    • Strings
    • Lists
    • Dictionaries
    • Booleans
    • Null
  • 3. Operators
    • Math Operations
    • Comparisons & Logic
    • Increment / Decrement
  • 4. Control Flow
    • IF Statements
    • WHILE Loops
    • FOR Loops
  • 5. Functions
    • Named Functions
    • Anonymous Functions
    • Closures
    • Recursion
  • 6. Object-Oriented Programming (OOP)
    • Classes and Instantiation
    • The SELF Keyword
    • Inheritance
    • Polymorphism
  • 7. Built-in Functions
• Error Handling
• Running Tests
• License

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About The Language

GladLang is an interpreter for a custom scripting language. It was built as a complete system, demonstrating the core components of a programming language:

• Lexer (lexer.py): A tokenizer that scans source code and converts it into a stream of tokens (e.g., NUMBER, STRING, IDENTIFIER, KEYWORD, PLUS).
• Parser (parser.py): A parser that takes the token stream and builds an Abstract Syntax Tree (AST), representing the code's structure.
• AST Nodes (nodes.py): A comprehensive set of nodes that define every syntactic structure in the language (e.g., BinOpNode, IfNode, FunDefNode, ClassNode).
• Runtime (runtime.py): Defines the Context and SymbolTable for managing variable scope, context (for tracebacks), and closures.
• Values (values.py): Defines the language's internal data types (Number, String, List, Function, Class, Instance).
• Interpreter (interpreter.py): The core engine that walks the AST and executes the program by visiting each node.
• Entry Point (gladlang.py): The main file that ties everything together. It handles command-line arguments, runs files, and starts the interactive shell.

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Key Features

GladLang supports a rich, modern feature set:

• Data Types: Numbers (int/float), Strings, Lists, Dictionaries, Booleans, and Null.
• Variables: Dynamic variable assignment with LET.
• Advanced Assignments:
  • Destructuring: Unpack lists directly (LET [x, y] = [1, 2]).
  • Slicing: Access sub-lists or substrings easily (list[0:3]).
• String Manipulation:
  • Interpolation: JavaScript-style template strings (`Hello ${name}`).
  • Multi-line Strings: Triple-quoted strings ("""...""") for large text blocks.
• List Comprehensions: Pythonic one-line list creation ([x * 2 FOR x IN list]).
• Dictionaries: Key-value data structures ({'key': 'value'}).
• Control Flow: IF, WHILE, FOR, BREAK, CONTINUE.
• Functions: First-class citizens, Closures, Recursion, Named/Anonymous support.
• Object-Oriented Programming: Classes, Inheritance, Polymorphism, SELF context.
• Built-ins: PRINT, INPUT, STR, INT, FLOAT, BOOL.
• Error Handling: Robust, user-friendly runtime error reporting with full tracebacks.
• Advanced Math: Power (**), Floor Division (//), and Modulo (%) operators.
• Rich Comparisons: Chained comparisons (1 < x < 10) and Identity checks (is).
• Flexible Logic: Support for and / or (case-insensitive).

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Getting Started

There are several ways to install and run GladLang.

1. Installation

Option A: Install via Pip (Recommended)

If you just want to use the language, install it via pip:

pip install gladlang

Option B: Install from Source (For Developers)

If you want to modify the codebase, clone the repository and install it in editable mode:

git clone https://github.com/gladw-in/gladlang.git
cd gladlang
pip install -e .

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2. Usage

Once installed, you can use the global gladlang command.

Interactive Shell (REPL)

Run the interpreter without arguments to start the shell:

gladlang

Running a Script

Pass a file path to execute a script:

gladlang "tests/test.glad"

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3. Running Without Installation (Source)

You can run the interpreter directly from the source code without installing it via pip:

python run.py "tests/test.glad"

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4. Building the Executable

You can build a standalone executable (no Python required) using PyInstaller:

pip install pyinstaller
pyinstaller run.py --paths src -F --name gladlang --icon=favicon.ico

This will create a single-file executable at dist/gladlang (or gladlang.exe on Windows).

Adding to PATH (Optional): To run the standalone executable from anywhere:

• Windows: Move it to a folder and add that folder to your System PATH variables.
• Mac/Linux: Move it to /usr/local/bin: sudo mv dist/gladlang /usr/local/bin/

---

Language Tour (Syntax Reference)

Here is a guide to the GladLang syntax, with examples from the tests/ directory.

1. Comments

Comments start with # and last for the entire line.

# This is a comment.
LET a = 10 # This is an inline comment

2. Variables and Data Types

Variables

Variables are assigned using the LET keyword. You can also unpack lists directly into variables using Destructuring.

LET a = 10
LET b = "Hello"
LET my_list = [a, b, 123]

# Destructuring Assignment
LET point = [10, 20]
LET [x, y] = point

PRINT x # 10
PRINT y # 20

Numbers

Numbers can be integers or floats. All standard arithmetic operations are supported.

LET math_result = (1 + 2) * 3 # 9
LET float_result = 10 / 4     # 2.5

Strings

Strings can be defined in three ways:

1. Double Quotes: Standard strings.
2. Triple Quotes: Multi-line strings that preserve formatting.
3. Backticks: Template strings supporting interpolation.

# Standard
LET s = "Hello\nWorld"

# Multi-line
LET menu = """
1. Start
2. Settings
3. Exit
"""

# Interpolation (Template Strings)
LET name = "Glad"
PRINT `Welcome back, ${name}!`
PRINT `5 + 10 = ${5 + 10}`

Lists, Slicing & Comprehensions

Lists are ordered collections. You can access elements, slice them, or create new lists dynamically using comprehensions.

LET nums = [0, 1, 2, 3, 4, 5]

# Indexing & Assignment
PRINT nums[1]        # 1
LET nums[1] = 100

# Slicing [start:end]
PRINT nums[0:3]      # [0, 1, 2]
PRINT nums[3:]       # [3, 4, 5]

# List Comprehension
LET squares = [n ** 2 FOR n IN nums]
PRINT squares        # [0, 1, 4, 9, 16, 25]

Dictionaries

Dictionaries are key-value pairs enclosed in {}. Keys must be Strings or Numbers.

LET person = {
  "name": "Glad",
  "age": 25,
  "is_admin": TRUE
}

PRINT person["name"]       # Access: "Glad"
LET person["age"] = 26     # Modify
LET person["city"] = "NYC" # Add new key

Booleans

Booleans are TRUE and FALSE. They are the result of comparisons and logical operations.

LET t = TRUE
LET f = FALSE
PRINT t AND f # 0 (False)
PRINT t OR f  # 1 (True)
PRINT NOT t   # 0 (False)

Truthiness: 0, 0.0, "", NULL, and FALSE are "falsy." All other values (including non-empty strings, non-zero numbers, lists, functions, and classes) are "truthy."

Null

The NULL keyword represents a null or "nothing" value. It is falsy and prints as 0. Functions with no RETURN statement implicitly return NULL.

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3. Operators

Math Operations

GladLang supports standard arithmetic plus advanced operators like Modulo, Floor Division, and Power.

PRINT 2 ** 3      # Power: 8
PRINT 10 // 3     # Floor Division: 3
PRINT 10 % 3      # Modulo: 1

# Standard precedence rules apply
PRINT 2 + 3 * 4   # 14
PRINT 1 + 2 * 3   # 7
PRINT (1 + 2) * 3 # 9

Comparisons & Logic

You can compare values, chain comparisons for ranges, and check object identity.

# Equality & Inequality
PRINT 1 == 1      # True
PRINT 1 != 2      # True

# Chained Comparisons (Ranges)
LET age = 25
IF 18 <= age < 30 THEN
  PRINT "Young Adult"
ENDIF

PRINT (10 < 20) AND (10 != 5) # 1 (True)

# Identity ('is' checks if variables refer to the same object)
LET a = [1, 2]
LET b = a
PRINT b is a      # True
PRINT b == [1, 2] # True (Values match)

# Boolean Operators (case-insensitive)
IF a and b THEN
  PRINT "Both exist"
ENDIF

Increment / Decrement

Supports C-style pre- and post-increment/decrement operators on variables and list elements.

LET i = 5
PRINT i++ # 5
PRINT i   # 6
PRINT ++i # 7
PRINT i   # 7

LET my_list = [10, 20]
PRINT my_list[1]++ # 20
PRINT my_list[1]   # 21

---

4. Control Flow

IF Statements

Uses IF...THEN...ENDIF syntax.

LET num = -5
IF num < 0 THEN
  PRINT "It is negative."
ENDIF

WHILE Loops

Loops while a condition is TRUE.

LET i = 3
WHILE i > 0
  PRINT "i = " + i
  LET i = i - 1
ENDWHILE

# Prints:
# i = 3
# i = 2
# i = 1

FOR Loops

Iterates over the elements of a list.

LET my_list = ["apple", "banana", "cherry"]
FOR item IN my_list
  PRINT "Item: " + item
ENDFOR

BREAK and CONTINUE are supported in both WHILE and FOR loops.

---

5. Functions

Named Functions

Defined with DEF...ENDEF. Arguments are passed by value. RETURN sends a value back.

DEF add(a, b)
  RETURN a + b
ENDEF

LET sum = add(10, 5)
PRINT sum # 15

Anonymous Functions

Functions can be defined without a name, perfect for assigning to variables.

LET double = DEF(x)
  RETURN x * 2
ENDEF

PRINT double(5) # 10

Closures

Functions capture variables from their parent scope.

DEF create_greeter(greeting)
  DEF greeter_func(name)
    # 'greeting' is "closed over" from the parent
    RETURN greeting + ", " + name + "!"
  ENDEF
  RETURN greeter_func
ENDEF

LET say_hello = create_greeter("Hello")
PRINT say_hello("Alex") # "Hello, Alex!"

Recursion

Functions can call themselves.

DEF fib(n)
  IF n <= 1 THEN
    RETURN n
  ENDIF
  RETURN fib(n - 1) + fib(n - 2)
ENDEF

PRINT fib(7) # 13

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6. Object-Oriented Programming (OOP)

Classes and Instantiation

Use CLASS...ENDCLASS to define classes and NEW to create instances. The constructor is init.

CLASS Counter
  DEF init(self)
    SELF.count = 0 # 'SELF' is the instance
  ENDEF
  
  DEF increment(self)
    SELF.count = SELF.count + 1
  ENDEF
  
  DEF get_count(self)
    RETURN SELF.count
  ENDEF
ENDCLASS

The SELF Keyword

SELF is the mandatory first argument for all methods and is used to access instance attributes and methods.

LET c = NEW Counter()
c.increment()
PRINT c.get_count() # 1

Inheritance

Use the INHERITS keyword. Methods can be overridden by the child class.

CLASS Pet
  DEF init(self, name)
    SELF.name = name
  ENDEF
  
  DEF speak(self)
    PRINT SELF.name + " makes a generic pet sound."
  ENDEF
ENDCLASS

CLASS Dog INHERITS Pet
  # Override the 'speak' method
  DEF speak(self)
    PRINT SELF.name + " says: Woof!"
  ENDEF
ENDCLASS

LET my_dog = NEW Dog("Buddy")
my_dog.speak() # "Buddy says: Woof!"

Polymorphism

When a base class method calls another method on SELF, it will correctly use the child's overridden version.

CLASS Pet
  DEF introduce(self)
    PRINT "I am a pet and I say:"
    SELF.speak() # This will call the child's 'speak'
  ENDEF
  
  DEF speak(self)
    PRINT "(Generic pet sound)"
  ENDEF
ENDCLASS

CLASS Cat INHERITS Pet
  DEF speak(self)
    PRINT "Meow!"
  ENDEF
ENDCLASS

LET my_cat = NEW Cat("Whiskers")
my_cat.introduce()
# Prints:
# I am a pet and I say:
# Meow!

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7. Built-in Functions

• PRINT(value): Prints a value to the console.
• INPUT(): Reads a line of text from the user as a String.
• STR(value): Casts a value to a String.
• INT(value): Casts a String or Float to an Integer.
• FLOAT(value): Casts a String or Integer to a Float.
• BOOL(value): Casts a value to its Boolean representation (TRUE or FALSE).

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Error Handling

GladLang features detailed error handling and prints full tracebacks for runtime errors, making debugging easy.

Example: Name Error (test_name_error.glad)

Traceback (most recent call last):
  File test_name_error.glad, line 6, in <program>
Runtime Error: 'b' is not defined

Example: Type Error (test_type_error.glad with input "5")

Traceback (most recent call last):
  File test_type_error.glad, line 6, in <program>
Runtime Error: Illegal operation

Example: Argument Error (test_arg_error.glad)

Traceback (most recent call last):
  File test_arg_error.glad, line 7, in <program>
  File test_arg_error.glad, line 4, in add
Runtime Error: Incorrect argument count for 'add'. Expected 2, got 3

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Running Tests

The tests/ directory contains a comprehensive suite of .glad files to test every feature of the language. You can run any test by executing it with the interpreter:

python gladlang.py "test_closures.glad"
python gladlang.py "test_lists.glad"
python gladlang.py "test_polymorphism.glad"

or

gladlang "test_closures.glad"
gladlang "test_lists.glad"
gladlang "test_polymorphism.glad"

License

You can use this under the MIT License. See LICENSE for more details.