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 is used to teach CS 164 at UC Berkeley. ChocoPy has been 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.
A paper on ChocoPy was presented at the 2019 ACM SIGPLAN SPLASH-E symposium in Athens, Greece.
# 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.")
The following resources are available for conducting a compilers course with ChocoPy:
These resources can be made available to instructors upon request.
# 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 email@example.com.