Static typing for all variables

• All variables must be defined before they are used (like in C++) and a type must be specified in each definition
• All languages must ensure that all variable assignments and expressions have compatible types; no implicit conversions are allowed.

Example:

func main void
    var int b c d     # b, c, and d are integer variables
    assign b 5
    var bool e        # e is a boolean variable
    assign e "foobar" # this would be a type error!
endfunc

Note: Even though Brewin++ is an interpreted language, by adding variable definitions with types, we enable all variable's types to be determined prior to execution, so a compiler could be written if we desired, making this a statically-typed language. But technically, it's still dynamically typed for now.

Brewin++ now implements lexical scoping for all variables, just like you'd see in C++. Here's an example program:

func main void
    var int a
    assign a 5
    if > a 0
        funccall print a # prints 5
        var string a     # legal: shadows our original a variable
        assign a "foobar"
        funccall print a # prints foobar
        var bool b
    endif
    funccall print a     # prints 5
    funccall print b     # Name error: b is out of scope
endfunc

Brewin++ now supports parameters for user-defined functions, and allows arguments to be passed to these functions by value or by reference. Functions also nowmust have an explicit return type. To access the return value from a function, you no longer refer to the result variable, but refer to resulti for integers, resultb for booleans, and results for strings.

Example:

# Equivalent to: bool absval(int val, int& change_me)
func absval val:int change_me:refint bool
    if < val 0
        assign change_me * -1 val
        return True
    else
        assign change_me val
        return False
    endif
endfunc

func main void
    var int val output
    assign val -5
    funccall absval val output
    funccall print "The absolute value is: " output
    funccall print "Did I negate the input value? " resultb
endfunc

Hey there! This is a template repository that contains the necessary boilerplate for CS 131's quarter-long project: making an interpreter. The project specs are as follows:

1. Project 1 Spec
2. Project 2 Spec
3. Project 3 - coming soon!

There are three stages to the project; students are currently at the second. Thus, this folder contains the necessary bootstrapping code:

• intbase.py, the base class and enum definitions for the interpreter
• a sample readme.txt, which should illustrate any known bugs/issues with the program (or, an "everything's good!")

As well as canonical solutions for Project 1 (written by Carey):

• interpreterv1.py: a top-level entrypoint: has some utility classes, finding the main function, the interpreter loop, and handlers for each token type
• env_v1.py: manages the "environment" / state for a program
• func_v1.py: manages and caches functions (will be much more useful in Project 2!)
• tokenize.py: tokenization logic

You do not have to use the canonical solutions for Project 2; in particular, since you didn't write the code, it may be confusing!

Some notes on your submission (for Project 2; we'll update this for later projects):

1. You must have a top-level, versioned interpreterv2.py file that exports the Interpreter class. If not, your code will not run on our autograder.
2. You may also submit one or more additional .py modules that your interpreter uses, if you decide to break up your solution into multiple .py files.

You can find out more about our autograder, including how to run it, in its accompanying repo.

This is an unlicensed repository; even though the source code is public, it is not governed by an open-source license.

This code was primarily written by Carey Nachenberg, with support from his TAs for the Fall 2022 iteration of CS 131.