Scheme is a dialect of the Lisp family of programming languages. It was created during the 1970s at the MIT Computer Science and Artificial Intelligence Laboratory (MIT CSAIL). This repository is a Python implementation of a Scheme Interpreter, which is Turing-complete and supports basic functionalities, including arithmetic operations, variables, if-else statements, lambda expressions, functions (w/ lexical scoping), recursion, iteration, file imports, and so much more. Below is a guide on basic Scheme syntax so that anyone can use the interpreter:

                                                |           Python          |           Scheme
                                                |                           |
         Arithmetic (applies to any operation)  |            2 + 3          |           (+ 2 3)
                                                |                           |
                  Variable Assignment           |            x = 5          |         (define x 5)
                                                |                           |
                   Defining Function            |   def craft(stick, wood): |   (define (craft stick wood)
                                                |     function body...      |      function body...  )                                                                                                

This is how inputs/outputs will appear within the interpreter (specifically in the terminal or console log):

                  in>  (define x 7)            in> (+ x 10)              in> x
                      out> 7                       out> 17                 out> 7          

Similarly, functions must be defined and then called like this:

                        in> (define (square x) (* x x))        in> (square 2)
                            out> FUNCTION OBJECT                   out> 4

How it works: To begin, run the 'run_interpreter.py' file, which will prompt the interpreter to start up in the console log/terminal. Text entered into the terminal is parsed through, (lines 30-119 under the functions 'tokenize' and 'parse'). Parsed text is then evaluated (via the 'evaluate' function on lines 528-640). This function is responsible for processing the many built-in and user-defined functions that make up the bulk of 'built_ins.py' (the names of all built-in functions can be found as a hash-map on lines 395-420 as 'scheme_builtins'). If the parsed text cannot be evaluated, a particular SchemeError message will pop up detailing why your code is not running. The general errors are concentrated in the 'errors.py'. A README file in the 'test_files' folder will instruct you on how you can import scheme files. Cheers!