pylox

Introduction

This is my Python implementation of an interpreter for the Lox programming language from Robert Nystrom's Crafting Interpreters.

Python?

While the text is implemented in Java and C as its high & low-level implementations, I have no idea how to write either of them! Instead, I'll be using Python for the high-level implementation & eventually Rust for the low-level imeplementation.

Differences From Text

For the sake of fitting within a decently sized text, the fully implemented Lox spec omits features that users of other programming languages may miss. Often these are discussed as notes within a chapter, or presented as challenges at the end of a chapter. Significant difference in this implementation from the text reference are noted below.

Defined by Challenges

• (Chapter 4): Arbitrarily nested block comments (/* ... */)
• (Chapter 9): break statements are available for for and while loops

User Choice

• Division by zero returns NaN (Python's float('nan'))
• Strings may be defined using either " or '
• Modulo operator (%)
• Power operator (^)
• Integer division operator (\)
• Both floats and integers are represented
  • Return type from operations follows Python3's semantics
• Containers
  • array()
• A basic include header system
  • Supports "stdlib" imports (<header_name>) and path imports ("path/to/file")
  • Recursive include not supported
  • Imported source assumed to be valid code

Additional Built-ins:

Unless otherwise noted, behavior mirrors the similarly named Python function.

General

• input
• len
• ord
• read_text (via pathlib.Path.read_text)
• str2num
• string_array
  • Gives a LoxArray whose contents are equivalent to collections.deque(<some string>)

Math

• abs
• ceil
• divmod
• floor
• max
• min

Regex

For methods whose Python equivalent returns Match objects, a LoxArray is returned. The first value in the array will always correspond to match.group(0); if the pattern contains one or more groups then the array will match the output of match.groups()

• re_findall
• re_match
• re_search
• re_sub

Stats

• mean
• median
• mode
• std

Pure lox headers

• <array_sum>
• <hello_world>
• <map>
• <split_on>