path: root/interpreter.py

from structs import *
from exceptions import *
from lexer import lex
from parser import parse
from pathlib import Path
from glob import glob
import subprocess
import shlex
import random
import sys

class Function:

    def __init__(self, name, params, body, *arities):
        self.name = name
        self.params = params
        self.body = body
        if len(arities) == 0:
            self.arities = None
        else:
            self.arities = arities

    def arity_check(self, symbol, args):
        if self.arities is not None and len(args) not in self.arities:
            fmt = ", ".join([f"{arity}" for arity in self.arities])
            raise InterpretPanic(symbol, f"expected [{fmt}] arguments, received {len(args)}")
        return True

    def call(self, expr, env):
        pass

class Builtin(Function):
    
    def __init__(self, callable_, *arities):
        super().__init__("<builtin>", None, callable_, *arities)

    def call(self, expr, env):
        self.arity_check(expr.args[0], expr.args[1:])
        return self.body(expr.args[0], expr.args[1:], env)

class UserFunction(Function):
    
    def __init__(self, name, params, body):
        super().__init__(name, params, body, len(params))

    def call(self, expr, env):
        self.arity_check(expr.args[0], expr.args[1:])
        this_env = Environment(env)
        for idx, param in enumerate(self.params):
            # TODO this is wrong!!! this won't always be a literal
            #this_env.register(param.name, Literal(evaluate(expr.args[idx+1],env)))
            this_env.register(param.name, evaluate(expr.args[idx+1],env))
        return interpret(self.body, this_env)

class Environment:
    
    def __init__(self, parent=None):
        self.parent = parent
        self.environment = {}

    def register(self, key, value):
        self.environment[key] = value

    def reregister(self, key, value):
        if not self.contains(key):
            raise NebPanic(f"undefined symbol: '{key}")
        if key in self.environment:
            self.register(key, value)
        else:
            self.parent.reregister(key, value)

    def contains(self, key):
        if key in self.environment:
            return True
        elif self.parent is not None:
            return self.parent.contains(key)
        else:
            return False

    def get(self, key):
        if not self.contains(key):
            raise NebPanic(f"undefined symbol: '{key}")
        if key in self.environment:
            return self.environment[key]
        else:
            return self.parent.get(key)

    def __str__(self):
        out = ""
        for k, v in self.environment.items():
            out += f"{k}: {v}, "
        return out

GLOBALS = Environment()

def interpret(exprs, env=GLOBALS):
    ret = None
    for expr in exprs:
        ret = evaluate(expr, env)
    return ret

def evaluate(expr, env):
    if isinstance(expr, Literal) or isinstance(expr, Function):
        #return expr.value
        return expr
    elif isinstance(expr, Symbol):
        if not env.contains(expr.name):
            raise NebPanic(f"no such symbol: {expr}")
        return evaluate(env.get(expr.name), env)

    # if it's a literal list, return it
    if expr.data:
        return expr
    # if it's an empty list, return it
    elif len(expr.args) == 0:
        return expr

    if not isinstance(expr.args[0], Symbol):
        raise NebPanic("can't evaluate without a symbol")
    name = expr.args[0].name
    if name == "def":
        return interpretDef(expr.args[0], expr.args[1:], env)
    elif env.contains(name):
        return env.get(name).call(expr, env)
    else:
        raise InterpretPanic(expr.args[0], "unable to evaluate")

def interpretOr(symbol, args, env):
    # or returns true for the first expression that returns true
    if len(args) < 2:
        raise InterpretPanic(symbol, "requires at least two arguments")
    for arg in args:
        ev = evaluate(arg, env)
        if not isinstance(ev, Bool):
            raise InterpretPanic(symbol, "requires :bool arguments")
        if ev.value == True:
            return ev
    return Bool(False)

GLOBALS.register("or", Builtin(interpretOr))

def interpretAnd(symbol, args, env):
    # and returns false for the first expression that returns false
    if len(args) < 2:
        raise InterpretPanic(symbol, "requires at least two arguments")
    for arg in args:
        ev = evaluate(arg, env)
        if not isinstance(ev, Bool):
            raise InterpretPanic(symbol, "requires :bool arguments")
        if ev.value == False:
            return ev
    return Bool(True)

GLOBALS.register("and", Builtin(interpretAnd))

def interpretEq(symbol, args, env):
    # equal
    # NOTE this currently only works for literals
    first = evaluate(args[0], env)
    second = evaluate(args[1], env)
    if not (isinstance(first, Literal) and isinstance(second, Literal)):
        raise InterpretPanic(symbol, "can only compare :literals")
    # compare types because 0 != #false in neb
    # TODO number equality?
    if type(first) == type(second) and first.value == second.value:
        return Bool(True)
    else:
        return Bool(False)

GLOBALS.register("eq?", Builtin(interpretEq, 2))

def interpretGreaterThan(symbol, args, env):
    left = evaluate(args[0], env)
    if not (isinstance(left, Int) or isinstance(left, Float)):
        raise InterpretPanic(symbol, "first argument must be a :number", left)
    right = evaluate(args[1], env)
    if not (isinstance(right, Int) or isinstance(right, Float)):
        raise InterpretPanic(symbol, "second argument must be a :number", right)
    return Bool(left.value > right.value)

GLOBALS.register(">", Builtin(interpretGreaterThan, 2))

def interpretGreaterThanEqual(symbol, args, env):
    left = evaluate(args[0], env)
    if not (isinstance(left, Int) or isinstance(left, Float)):
        raise InterpretPanic(symbol, "first argument must be a :number", left)
    right = evaluate(args[1], env)
    if not (isinstance(right, Int) or isinstance(right, Float)):
        raise InterpretPanic(symbol, "second argument must be a :number", right)
    return Bool(left.value >= right.value)

GLOBALS.register(">=", Builtin(interpretGreaterThanEqual, 2))

def interpretLessThan(symbol, args, env):
    left = evaluate(args[0], env)
    if not (isinstance(left, Int) or isinstance(left, Float)):
        raise InterpretPanic(symbol, "first argument must be a :number", left)
    right = evaluate(args[1], env)
    if not (isinstance(right, Int) or isinstance(right, Float)):
        raise InterpretPanic(symbol, "second argument must be a :number", right)
    return Bool(left.value < right.value)

GLOBALS.register("<", Builtin(interpretLessThan, 2))

def interpretLessThanEqual(symbol, args, env):
    left = evaluate(args[0], env)
    if not (isinstance(left, Int) or isinstance(left, Float)):
        raise InterpretPanic(symbol, "first argument must be a :number", left)
    right = evaluate(args[1], env)
    if not (isinstance(right, Int) or isinstance(right, Float)):
        raise InterpretPanic(symbol, "second argument must be a :number", right)
    return Bool(left.value <= right.value)

GLOBALS.register("<=", Builtin(interpretLessThanEqual, 2))

def interpretAddition(symbol, args, env):
    if len(args) < 1:
        raise InterpretPanic(symbol, "requires at least one argument")
    res = 0
    for arg in args:
        ev = evaluate(arg, env)
        if not (isinstance(ev, Int) or isinstance(ev, Float)):
            raise InterpretPanic(symbol, "argument must be a :number", ev)
        res += ev.value
    if isinstance(res, float):
        return Float(res)
    else:
        return Int(res)

GLOBALS.register("+", Builtin(interpretAddition))

def interpretSubtraction(symbol, args, env):
    if len(args) < 1:
        raise InterpretPanic(symbol, "requires at least one argument")
    first = evaluate(args[0], env)
    if not (isinstance(first, Int) or isinstance(first, Float)):
        raise InterpretPanic(symbol, "argument must be a :number", first)
    if len(args) == 1:
        res = -first.value
    else:
        res = first.value
    for arg in args[1:]:
        ev = evaluate(arg, env)
        if not (isinstance(ev, Int) or isinstance(ev, Float)):
            raise InterpretPanic(symbol, "argument must be a :number", ev)
        res -= ev.value
    if isinstance(res, float):
        return Float(res)
    else:
        return Int(res)

GLOBALS.register("-", Builtin(interpretSubtraction))

def interpretMultiplication(symbol, args, env):
    if len(args) < 2:
        raise InterpretPanic(symbol, "requires at least two arguments")
    first = evaluate(args[0], env)
    if not (isinstance(first, Int) or isinstance(first, Float)):
        raise InterpretPanic(symbol, "argument must be a :number", first)
    res = first.value
    for arg in args[1:]:
        tmp = evaluate(arg, env)
        if not (isinstance(tmp, Int) or isinstance(tmp, Float)):
            raise InterpretPanic(symbol, "argument must be a :number", tmp)
        res = res * tmp.value
    if isinstance(res, float):
        return Float(res)
    else:
        return Int(res)

GLOBALS.register("*", Builtin(interpretMultiplication))

def interpretDivision(symbol, args, env):
    num = evaluate(args[0], env)
    if not (isinstance(num, Int) or isinstance(num, Float)):
        raise InterpretPanic(symbol, "numerator must be a :number", num)
    denom = evaluate(args[1], env)
    if not (isinstance(denom, Int) or isinstance(denom, Float)):
        raise InterpretPanic(symbol, "denominator must be a :number", denom)
    ret = num.value / denom.value
    if int(ret) == ret:
        return Int(int(ret))
    else:
        return Float(ret)

GLOBALS.register("/", Builtin(interpretDivision, 2))

def interpretNot(symbol, args, env):
    res = evaluate(args[0], env)
    if not isinstance(res, Bool):
        raise InterpretPanic(symbol, "requires a :bool", res)
    return Bool(not res.value)

GLOBALS.register("not", Builtin(interpretNot, 1))

def interpretIf(symbol, args, env):
    # if cond t-branch [f-branch]
    cond = evaluate(args[0], env)
    if not isinstance(cond, Bool):
        raise InterpretPanic(symbol, "condition must be :bool", cond)
    if cond.value:
        return evaluate(args[1], env)
    elif len(args) == 3:
        return evaluate(args[2], env)
    return List([])  # this shouldn't be reached

GLOBALS.register("if", Builtin(interpretIf, 2, 3))

def interpretPrint(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, String):
        raise InterpretPanic(symbol, "requires a :string")
    print(ev.value)

    return List([])  # print returns nothing

GLOBALS.register("print", Builtin(interpretPrint, 1))

def interpretDef(symbol, args, env):
    if not isinstance(args[0], Symbol):
        raise InterpretPanic(symbol, "requires a :string name", args[0])
    name = args[0].name  # NOTE: we are not evaluating the name!!
    if not isinstance(name, str):
        raise InterpretPanic(symbol, "requires a :string name")

    ev = evaluate(args[1], env)
    env.register(name, ev)
    return List([])

GLOBALS.register("def", Builtin(interpretDef, 2))

def interpretRedef(symbol, args, env):
    if not isinstance(args[0], Symbol):
        raise InterpretPanic(symbol, "requires a :string name", args[0])
    name = args[0].name  # NOTE: we are not evaluating the name!!
    if not env.contains(name):
        raise InterpretPanic(symbol, "not previously defined", args[0])

    ev = evaluate(args[1], env)
    env.reregister(name, ev)
    return List([])

GLOBALS.register("redef", Builtin(interpretRedef, 2))

def interpretLambda(symbol, args, env):
    if len(args[0].args) != 0:
        func = UserFunction("<lambda>", args[0].args, args[1:])
    else:
        func = UserFunction("<lambda>", [], args[1:])
    return func

GLOBALS.register("lambda", Builtin(interpretLambda))

def interpretToString(symbol, args, env):
    ev = evaluate(args[0], env)
    if isinstance(ev, String):
        return ev
    elif isinstance(ev, Literal):
        return String(str(ev))
    else:
        return String(f"{ev}")

GLOBALS.register("->string", Builtin(interpretToString, 1))

def interpretConcat(symbol, args, env):
    # concat str1 str2...strN
    if len(args) < 2:
        raise InterpretPanic(symbol, "requires at least two arguments")
    out = ""
    for arg in args:
        tmp = evaluate(arg, env)
        if not isinstance(tmp, String):
            raise InterpretPanic(symbol, "requires :string", tmp)
        out += tmp.value
    return String(out)

GLOBALS.register("concat", Builtin(interpretConcat))

def interpretForCount(symbol, args, env):
    # for-count int exprs
    num = evaluate(args[0], env)
    if not isinstance(num, Int):
        raise InterpretPanic(symbol, "count must be an integer", num)
    new_env = Environment(env)
    ret = None
    for idx in range(0, num.value):
        new_env.register("idx", Int(idx + 1))
        for arg in args[1:]:
            ret = evaluate(arg, new_env)
    if ret is None:
        return List([])
    return ret

GLOBALS.register("for-count", Builtin(interpretForCount))

def interpretForEach(symbol, args, env):
    # for-each list exprs
    lst = evaluate(args[0], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbok, "requires a :list", lst)
    new_env = Environment(env)
    ret = None
    for item in lst.args:
        new_env.register("_item_", evaluate(item, env))
        for arg in args[1:]:
            ret = evaluate(arg, new_env)
    if ret is None:
        return List([])
    return ret

GLOBALS.register("for-each", Builtin(interpretForEach))

def interpretPipe(symbol, args, env):
    if len(args) < 2:
        raise InterpretPanic(symbol, "requires at least two expressions")
    new_env = Environment(env)
    pipe = None
    for arg in args:
        if pipe is not None:
            new_env.register("items", pipe)
        pipe = evaluate(arg, new_env)
    if pipe is None:
        return List([])
    return pipe

GLOBALS.register("|", Builtin(interpretPipe))

def interpretBranch(symbol, args, env):
    if len(args) == 0:
        raise InterpretPanic(symbol, "requires at least one pair of expressions")
    for arg in args:
        if len(arg.args) != 2:
            raise InterpretPanic(symbol, "each branch requires two expressions")
        cond = evaluate(arg.args[0], env)  # this is the condition
        if not isinstance(cond, Bool):
            raise InterpretPanic(symbol, "branch condition must be :bool", cond)
        if cond.value:
            return evaluate(arg.args[1], env)
    return List([])

GLOBALS.register("branch", Builtin(interpretBranch))

def interpretFunc(symbol, args, env):
    # func <name> (args) (exprs)
    if len(args) < 3:
        raise InterpretPanic(symbol, "requires a name, argument list, and at least one expression")
    if not isinstance(args[0], Symbol):
        raise InterpretPanic(symbol, "requires a :string name")
    name = args[0].name  # NOTE: we are not evaluating the name!!

    # compose a lambda
    func = interpretLambda(None, args[1:], env)

    env.register(name, func)
    return List([])

GLOBALS.register("func", Builtin(interpretFunc))

# THINGS NEEDED FOR AOC
#  - read the contents of a file
def interpretReadLines(symbol, args, env):
    target_file_name = evaluate(args[0], env).value
    target_file = Path(target_file_name).resolve()
    if not target_file.exists():
        raise InterpretPanic(symbol, "no such file", target_file)
    with open(target_file, "r") as fil:
        data = fil.readlines()
    out = List([String(d) for d in data], True) # all lines are strings
    return out

GLOBALS.register("read-lines", Builtin(interpretReadLines, 1))

#  - strip whitespace from string
def interpretStrip(symbol, args, env):
    out = evaluate(args[0], env)
    if not isinstance(out, String):
        raise InterpretPanic(symbol, "requires a :string", out)
    return String(out.value.strip())

GLOBALS.register("strip", Builtin(interpretStrip, 1))

#  - string->int and string->float
def interpretStringToInt(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, String):
        raise InterpretPanic(symbol, "requires a :string", ev)
    try:
        val = int(ev.value)
        return Int(val)
    except:
        raise InterpretPanic(symbol, "can't convert to an :int", ev)

GLOBALS.register("string->int", Builtin(interpretStringToInt, 1))

#  - split a string by a given field
def interpretSplit(symbol, args, env):
    target = evaluate(args[0], env)
    if not isinstance(target, String):
        raise InterpretPanic(symbol, "requires a :string as its first argument", target)
    if len(args) == 1:
        return List([String(char) for char in target.value], True)
    splitter = evaluate(args[1], env)
    if not isinstance(splitter, String):
        raise InterpretPanic(symbol, "requires a :string as its second argument", splitter)
    ret = target.value.split(splitter.value)
    return List([String(r) for r in ret], True)

GLOBALS.register("split", Builtin(interpretSplit, 1, 2))
    
#  - get the length of a list
def interpretListLength(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, List):
        raise InterpretPanic(symbol, "requires a :list", ev)
    return Int(len(ev.args))

GLOBALS.register("list-length", Builtin(interpretListLength, 1))
    
#  - first/rest of list
def interpretFirst(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, List):
        raise InterpretPanic(symbol, "requires a :list", ev)
    if len(ev.args) == 0:
        raise InterpretPanic(symbol, "list is empty")
    return evaluate(ev.args[0], env)

GLOBALS.register("first", Builtin(interpretFirst, 1))

def interpretRest(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, List):
        raise InterpretPanic(symbol, "requires a :list", ev)
    # TODO do we know it's not evaluated?
    return List(ev.args[1:], True) # we don't evaluate the remainder of the list

GLOBALS.register("rest", Builtin(interpretRest, 1))

#  - iterate over list
#  - map
def interpretMap(symbol, args, env):
    # TODO: to support lambdas, we can't assume the func is defined
    func = args[0]
    if not isinstance(func, Symbol):
        raise InterpretPanic(symbol, "requires a symbol as its first argument", func)
    lst = evaluate(args[1], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbol, "requires a :list as its second argument", lst)
    out = []
    for arg in lst.args:
        ev = evaluate(List([func, arg]), env)
        out.append(ev)
    return List(out, True)

GLOBALS.register("map", Builtin(interpretMap, 2))

def interpretZip(symbol, args, env):
    z1 = evaluate(args[0], env)
    if not isinstance(z1, List):
        raise InterpretPanic(symbol, "requires two :lists", z1)
    z2 = evaluate(args[1], env)
    if not isinstance(z2, List):
        raise InterpretPanic(symbol, "requires two :lists", z2)
    if len(z1.args) != len(z2.args):
        raise InterpretPanic(symbol, "requires two :lists of the same size")
    out = []
    for idx in range(len(z1.args)):
        f = evaluate(z1.args[idx], env)
        s = evaluate(z2.args[idx], env)
        out.append(List([f, s], True))
    return List(out, True)

GLOBALS.register("zip", Builtin(interpretZip, 2))

def interpretList(symbol, args, env):
    out = []
    for arg in args:
        out.append(evaluate(arg, env))
    return List(out, True)

GLOBALS.register("list", Builtin(interpretList))

def interpretListReverse(symbol, args, env):
    lst = evaluate(args[0], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbol, "requires a :list", lst)
    new_args = lst.args[:] # make a copy of the args
    new_args.reverse()
    return List(new_args, True)

GLOBALS.register("list-reverse", Builtin(interpretListReverse, 1))

def interpretApply(symbol, args, env):
    func = args[0]
    if not isinstance(func, Symbol):
        raise InterpretPanic(symbol, "requires a symbol as its first argument", func)
    lst = evaluate(args[1], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbol, "requires a :list as its second argument". lst)
    new_lst = List([func] + lst.args)
    return evaluate(new_lst, env)

GLOBALS.register("apply", Builtin(interpretApply, 2))

def interpretGlob(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, String):
        raise InterpretPanic(symbol, "requires a :string", ev)
    items = glob(ev.value)
    return List([String(item) for item in items], True)

GLOBALS.register("glob", Builtin(interpretGlob, 1))

def interpretShell(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, String):
        raise InterpretPanic(symbol, "requires a :string", ev)
    # TODO either fail or throw exception (?) on error
    ret = subprocess.run(shlex.split(ev.value), capture_output=True)
    return List([String(r) for r in ret.stdout.decode("utf-8").split("\n")], True)

GLOBALS.register("$", Builtin(interpretShell, 1))

def interpretEmpty(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, List):
        raise InterpretPanic(symbol, "requires a :list", ev)
    return Bool(len(ev.args) == 0)

GLOBALS.register("empty?", Builtin(interpretEmpty, 1))

def interpretShuf(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, List):
        raise InterpretPanic(symbol, "expects a :list", ev)
    items = ev.args[:]
    random.shuffle(items)
    return List(items, True)

GLOBALS.register("shuf", Builtin(interpretShuf, 1))

def interpretIsList(symbol, args, env):
    ev = evaluate(args[0], env)
    return Bool(isinstance(ev, List))

GLOBALS.register("list?", Builtin(interpretIsList, 1))

def interpretBlock(symbol, args, env):
    ret = List([])
    for arg in args:
        ret = evaluate(arg, env)
    return ret

GLOBALS.register("block", Builtin(interpretBlock))

def interpretExit(symbol, args, env):
    if len(args) > 1:
        raise InterpretPanic(symbol, "expects one (optional) argument")
    status = 0 if len(args) == 0 else evaluate(args[0], env).value
    if not isinstance(status, int):
        raise InterpretPanic(symbol, "expects an :int", status)
    sys.exit(status)
    return List([])

GLOBALS.register("exit", Builtin(interpretExit, 0, 1))

def interpretUnlink(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, String):
        raise InterpretPanic(symbol, "expects a :string", ev)
    target_path = Path(ev.value).resolve()
    if not target_path.exists():
        raise InterpretPanic(symbol, "target file does not exist", target_path)
    target_path.unlink()
    return List([])

GLOBALS.register("unlink", Builtin(interpretUnlink, 1))

def interpretArgv(symbol, args, env):
    out = []
    for arg in sys.argv[1:]:
        out.append(String(arg))
    return List(out, True)

GLOBALS.register("argv", Builtin(interpretArgv, 0))

def interpretIn(symbol, args, env):
    target = evaluate(args[0], env)
    if not isinstance(target, Literal):
        raise InterpretPanic(symbol, "expects a :literal as its first argument", target)
    lst = evaluate(args[1], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbol, "expects a :list as its second argument", lst)
    for arg in lst.args:
        ev = evaluate(arg, env)
        if type(ev) == type(target) and ev.value == target.value:
            return Bool(True)
    return Bool(False)

GLOBALS.register("in?", Builtin(interpretIn, 2))

def interpretLast(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, List):
        raise InterpretPanic("'last' expects a List")
    if len(ev.args) == 0:
        raise InterpretPanic("List is empty")
    return evaluate(ev.args[-1], env)

GLOBALS.register("last", Builtin(interpretLast, 1))

def interpretJoin(symbol, args, env):
    lst = evaluate(args[0], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbol, "expects a :list as its first argument", lst)
    target = evaluate(args[1], env)
    if not isinstance(target, String):
        raise InterpretPanic(symbol, "expects a :string as its second argument", target)
    return String(target.value.join(lst.args))

GLOBALS.register("join", Builtin(interpretJoin, 2))

def interpretWithWrite(symbol, args, env):
    if len(args) == 0:
        raise InterpretPanic(symbol, "expects at least one argument")
    target_file = evaluate(args[0], env)
    if not isinstance(target_file, String):
        raise InterpretPanic(symbol, "expects a :string as its first argument", target_file)
    new_env = Environment(env)
    target_path = Path(target_file.value).resolve()
    ret = Literal([])
    with open(str(target_path), "w") as fil:
        new_env.register("_file_", List([fil], True)) # TODO wrong!
        for arg in args[1:]:
            ret = evaluate(arg, new_env)
    return ret

GLOBALS.register("with-write", Builtin(interpretWithWrite))

def interpretWrite(symbol, args, env):
    # write :string :filehandle
    line = evaluate(args[0], env)
    if not isinstance(line, String):
        raise InterpretPanic(symbol, "expects a :string as its first argument", line)
    handle = evaluate(args[1], env)
    handle.args[0].write(line.value)  # TODO wrong! how do we evaluate a handle?
    return Literal([])

GLOBALS.register("write", Builtin(interpretWrite, 2))

def interpretNewline(symbol, args, env):
    return String("\n")

GLOBALS.register("newline", Builtin(interpretNewline, 0))

def interpretExists(symbol, args, env):
    file_or_dir = evaluate(args[0], env)
    if not isinstance(file_or_dir, String):
        raise InterpretPanic(symbol, "expects a :string", file_or_dir)
    return Bool(Path(file_or_dir.value).resolve().exists())

GLOBALS.register("exists?", Builtin(interpretExists, 1))

def interpretFirstChar(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, String):
        raise InterpretPanic(symbol, "expects a :string", ev)
    if len(ev.value) == 0:
        raise InterpretPanic(symbol, ":string is empty", ev)
    return String(ev.value[0])

GLOBALS.register("first-char", Builtin(interpretFirstChar, 1))

def interpretRestChar(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, String):
        raise InterpretPanic(symbol, "expects a string", ev)
    return String(ev.value[1:])

GLOBALS.register("rest-char", Builtin(interpretRestChar, 1))

def interpretSlice(symbol, args, env):
    lst = evaluate(args[0], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbol, "expects a :list as its first argument", lst)
    idx = evaluate(args[1], env)
    if not isinstance(idx, Int):
        raise InterpretPanic(symbol, "expects an :int as its second argument", idx)
    if len(args) == 2:
        return List(lst.args[idx.value - 1:])
    length = evaluate(args[2], env)
    if not isinstance(length, Int):
        raise InterpretPanic(symbol, "expects an :int as its third argument", length)
    diff = idx.value - 1 + length.value
    return List(lst.args[idx.value - 1:diff])

GLOBALS.register("slice", Builtin(interpretSlice, 2, 3))

def interpretClear(symbol, args, env):
    subprocess.run(["clear"])
    return List([])

GLOBALS.register("clear", Builtin(interpretClear, 0))

def interpretInput(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, String):
        raise InterpretPanic(symbol, "expects a :string", ev)
    ret = input(ev.value)
    return String(ret)

GLOBALS.register("input", Builtin(interpretInput, 1))

def interpretAppend(symbol, args, env):
    lst = evaluate(args[0], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbol, "expects a :list as its first argument", lst)
    val = evaluate(args[1], env)
    items = lst.args[:]
    return List(items + [val], True)

GLOBALS.register("append", Builtin(interpretAppend, 2))

def interpretRemove(symbol, args, env):
    lst = evaluate(args[0], env)
    if not isinstance(lst, List):
        raise InterpretPanic(symbol, "expects a :list as its first argument", lst)
    key = evaluate(args[1], env)
    out = []
    for arg in lst.args:
        if arg.args[0].value != key.value:
            out.append(arg)
    return List(out, True)

GLOBALS.register("remove", Builtin(interpretRemove, 2))

def interpretWhile(symbol, args, env):
    cond = args[0]
    ret = List([])
    while True:
        ev = evaluate(cond, env)
        if not isinstance(ev, Bool):
            raise InterpretPanic(symbol, "expects a :bool condition", ev)
        if not ev.value:
            break
        for arg in args[1:]:
            ret = evaluate(arg, env)
    return ret

GLOBALS.register("while", Builtin(interpretWhile))

def interpretAnsiEscape(symbol, args, env):
    return String(f"\033")

GLOBALS.register("ansi-escape", Builtin(interpretAnsiEscape, 0))

def interpretUse(symbol, args, env):
    target_file_name = evaluate(args[0], env).value
    target_file = Path(target_file_name).resolve()
    if not target_file.exists():
        raise InterpretPanic(symbol, "no such file", target_file)
    with open(target_file, "r") as fil:
        data = fil.read()
    interpret(parse(lex(data)))
    return List([])

GLOBALS.register("use", Builtin(interpretUse, 1))