ChocoPy is a programming language designed for classroom use in undergraduate compilers courses. ChocoPy is a restricted subset of Python 3, which can easily be compiled to a target such as RISC-V. The language is fully specified using formal grammar, typing rules, and operational semantics. ChocoPy was originally used to teach CS 164 at UC Berkeley, but has since been used by several other institutions. ChocoPy was designed by Rohan Padhye and Koushik Sen, with substantial contributions from Paul Hilfinger.
At a glance, ChocoPy is:
Bonus: Due to static type safety and ahead-of-time compilation, most student implementations outperform the reference Python implementation on non-trivial benchmarks.
# Search in a list def contains(items:[int], x:int) -> bool: i:int = 0 while i < len(items): if items[i] == x: return True i = i + 1 return False if contains([4, 8, 15, 16, 23], 15): print("Item found!") # Prints this else: print("Item not found.")
Rohan Padhye, Koushik Sen, and Paul N. Hilfinger. 2019. ChocoPy: A Programming Language for Compilers Courses. In Proceedings of the 2019 ACM SIGPLAN SPLASH-E Symposium (SPLASH-E ’19), October 25, 2019, Athens, Greece. ACM, New York, NY, USA, 5 pages. https://doi.org/10.1145/3358711.3361627
Download: Paper PDF (1MB) | Slides PDF (90MB)
The following resources are available for conducting a compilers course with ChocoPy:
These resources can be made available to instructors upon request.
From personal communication, we have been made aware of ChocoPy being used to teach compiler construction at TU Delft (with Spoofax), at UC San Diego (targeting WebAssembly) and at NYU. The auto-grading infrastructure was extracted for use at UCLA. The language spec was used as a reference at IIT Bombay.
# A broken program def is_even(x:int) -> bool: if x % 2 == 1: return 0 # FIXME else: return True print(is_even("3")) # FIXME
# Compute x**y def exp(x: int, y: int) -> int: a: int = 0 global invocations # Count calls to this function def f(i: int) -> int: nonlocal a def geta() -> int: return a if i <= 0: return geta() else: a = a * x return f(i-1) a = 1 invocations = invocations + 1 return f(y) invocations:int = 0 print(exp(2, 10)) print(exp(3, 3)) print(invocations)
# A resizable list of integers class Vector(object): # Attributes items: [int] = None size: int = 0 # Constructor def __init__(self:"Vector"): self.items =  # Returns current capacity def capacity(self:"Vector") -> int: return len(self.items) # Increases capacity of vector by one element def increase_capacity(self:"Vector") -> int: self.items = self.items +  return self.capacity() # Appends one item to end of vector def append(self:"Vector", item: int): if self.size == self.capacity(): self.increase_capacity() self.items[self.size] = item self.size = self.size + 1 # A faster (but more memory-consuming) implementation of vector class DoublingVector(Vector): doubling_limit:int = 16 # Overriding to do fewer resizes def increase_capacity(self:"DoublingVector") -> int: if (self.capacity() <= self.doubling_limit // 2): self.items = self.items + self.items else: # If doubling limit has been reached, fall back to # standard capacity increases self.items = self.items +  return self.capacity() vec:Vector = None num:int = 0 # Create a vector and populate it with The Numbers vec = DoublingVector() for num in [4, 8, 15, 16, 23, 42]: vec.append(num) print(vec.capacity())
ChocoPy does not support modules and imports, higher order functions, native dictionaries, and exceptions.
Want to use ChocoPy to run your own compilers course? Send an email to firstname.lastname@example.org.
If you would like to reference ChocoPy in a research paper, please cite the SPLASH-E paper.