scheme_subtitue.py

from util import *
from functools import reduce

env = { }

def clean_env():
    global env
    env = {}

def isprimitive(sexp):
    return isinstance(sexp, int) or isinstance(sexp, float)

def substitute(sexp, name, value):
    if sexp == name:
        return value
    elif isinstance(sexp, tuple):
        result = [ ]
        for item in sexp:
            result.append(substitute(item, name, value))
        return tuple(result)
    else:
        return sexp


def seval(sexp):
    if isprimitive(sexp):
        return sexp
    # builtins
    if isinstance(sexp, str) and sexp in env:
        return env[sexp]
    if isinstance(sexp, str) and sexp in builtins:
        return builtins[sexp]

    if isinstance(sexp, str):
        return sexp

    if isinstance(sexp, tuple):
        if sexp[0] == 'define':
            name = sexp[1]
            value = seval(sexp[2])
            env[name] = value
            return None

        if sexp[0] == 'set!':
            name = sexp[1]
            value = seval(sexp[2])
            # Go Find the previous definition and change it
            env[name] = value
            return None

        if sexp[0] == 'if':
            test = seval(sexp[1])
            if test:
                return seval(sexp[2])
            else:
                return seval(sexp[3])
        if sexp[0] == 'cond':
            for exp in sexp[1:]:
                test_expr = exp[0]
                if test_expr == 'else' or seval(test_expr):
                    return seval(exp[1])
                else:
                    continue
        if sexp[0] == 'begin':
            for e in sexp[1:]:
                r = seval(e)
            return r
        if sexp[0] == 'let':
            names = [b[0] for b in sexp[1]]
            values = [b[1] for b in sexp[1]]

            for exp in sexp[2:]:
                for name, value in zip(names, values):
                    exp = substitute(exp, name, value)
                r = seval(exp)
            return r

        if sexp[0] == 'lambda':
            def procedure(*args):
                argnames = sexp[1]
                body = sexp[2]
                for n in range(len(argnames)):
                    body = substitute(body, argnames[n], args[n])
                return seval(body)

            return procedure

        proc = seval(sexp[0])
        args = []
        for arg in sexp[1:]:
            args.append(seval(arg))
        # print(f"{proc=}")
        return proc(*args)



if __name__ == "__main__":
    # run file
    import sys
    with open(sys.argv[1], "r") as f:
        lines = f.readlines()
        for line in lines:
            if line.startswith("#") or line.startswith(";") or line.startswith("(require"):
                continue
            r1 = seval(translate(line))
        
    print(r1)