Lets build a simple interpreter from scratch in python, pt.01

#interpreter #fromscratch #python

Hi!.
In this blog series we will see that will i be sucessful or not in my attempt to build a programming language, an interpreter, a parser, a compiler and a virtual machine. For any questions starting with 'why' the answer is always 'why not?' except theese:

Why Python? Python lets you focus on problem rather than fighting with language itself.
Why not Rust? Rust is causing hair loss while fighting against it.
Why not C? It explodes many times in your hands. You lose your hands.

If code that i write is not idiomatic and tastefull for you please ignore it.
Lets get started.

class Interpreter:
    def __init__(self):
        pass

    def run(self,code):
        for xs in code:
            self.eval(xs)


    # This is our magic function. It evauates xs parameter 
    # according to its first element  and calls appropriate 
    # member function and passes the parameter to that function.
    # If xs is not a list then returns xs itself:

    def eval(self,xs):
        if isinstance(xs,list):
            return self.__getattribute__(xs[0])(xs)
        return xs


    # Our first function (or opcode) is Print. If last item 
    # is a comma it doesn't print newline:  

    def Print(self,xs):
        if len(xs)==1:
            print()
            return
        l=len(xs)-1
        for i,x in enumerate(xs[1:]):
            e=self.eval(x)
            if i<l-1:
                print(e,end="")
            else:
                if e!=",":
                    print(e)
                else:
                    print(e,end="")

# This is AST (Abstract Syntax Tree) generated by 
# parser. Consisting of recursive lists
# (No, not lisp :P )
code=[
    ["Print","Hello World!","Sky is blue"],
    ["Print",1,","],
    ["Print",2,","],
    ["Print",3],
    ["Print","a"],
    ["Print","b"],
    ["Print"],
    ["Print","c"],
]

interpreter=Interpreter()

interpreter.run(code)