path: root/interpreter.py

from structs import Literal, Symbol, List
from pathlib import Path

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 call(self, expr, env):
        pass

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

    def call(self, expr, env):
        if self.arities is not None and len(expr.args[1:]) not in self.arities:
            fmt = f"[{self.arities[0]}"
            for arity in self.arities[1:]:
                fmt += f", {arity}"
            fmt += "]"
            raise Exception(f"expected {fmt} arguments, received {len(expr.args)}")
        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):
        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 Exception(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 Exception(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):
        #return expr.value
        return expr
    elif isinstance(expr, Symbol):
        if not env.contains(expr.name):
            raise Exception(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 Exception("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 Exception(f"unable to evaluate: {expr}")

def interpretOr(symbol, args, env):
    # or returns true for the first expression that returns true
    if len(args) < 2:
        raise Exception("'or' has at least two operands")
    for arg in args:
        ev = evaluate(arg, env)
        #if ev not in (True, False):
        if not isinstance(ev, Literal) and ev.value not in (True, False):
            raise Exception("'or' needs boolean arguments")
        if ev.value == True:
            return ev
    return Literal(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 Exception("'and' has at least two operands")
    for arg in args:
        ev = evaluate(arg, env)
        #if ev not in (True, False):
        if not isinstance(ev, Literal) and ev.value not in (True, False):
            raise Exception("'and' needs boolean arguments")
        if ev.value == False:
            return ev
    return Literal(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 Exception("'eq?' can only compare literals")
    if first.value == second.value:
        return Literal(True)
    else:
        return Literal(False)

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

def interpretComparison(symbol, args, env):
    left = evaluate(args[0], env)
    if not isinstance(left, Literal) or type(left.value) not in (int, float):
        raise Exception("'left' must be a number")
    right = evaluate(args[1], env)
    if not isinstance(right, Literal) or type(right.value) not in (int, float):
        raise Exception("'right' must be a number")

    if symbol.name == ">":
        return Literal(left.value > right.value)
    elif symbol.name == ">=":
        return Literal(left.value >= right.value)
    elif symbol.name == "<":
        return Literal(left.value < right.value)
    elif symbol.name == "<=":
        return Literal(left.value <= right.value)

GLOBALS.register(">", Builtin(interpretComparison, 2))
GLOBALS.register(">=", Builtin(interpretComparison, 2))
GLOBALS.register("<", Builtin(interpretComparison, 2))
GLOBALS.register("<=", Builtin(interpretComparison, 2))

def interpretTerm(symbol, args, env):
    if len(args) < 1:
        raise Exception("term has at least one operand")
    res = None
    for arg in args:
        ev = evaluate(arg, env)
        if not isinstance(ev, Literal) or type(ev.value) not in (int, float):
            raise Exception("term must be a number")
        if res is None:
            res = ev.value
        elif symbol.name == "+":
            res += ev.value
        elif symbol.name == "-":
            res -= ev.value
    return Literal(res)

GLOBALS.register("+", Builtin(interpretTerm))
GLOBALS.register("-", Builtin(interpretTerm))

def interpretFactor(symbol, args, env):
    if symbol.name == "/":
        num = evaluate(args[0], env)
        if not isinstance(num, Literal) or type(num.value) not in (int, float):
            raise Exception("numerator must be a number")
        denom = evaluate(args[1], env)
        if not isinstance(denom, Literal) or type(denom.value) not in (int, float):
            raise Exception("denominator must be a number")
        ret = num.value / denom.value
        if int(ret) == ret:
            return Literal(int(ret))
        else:
            return Literal(ret)
    else:
        if len(args) < 2:
            raise Exception("'*' requires at least two operands")
        first = evaluate(args[0], env)
        if not isinstance(first, Literal) or type(first.value) not in (int, float):
            raise Exception("'*' operand must be a number")
        res = first.value
        for arg in args[1:]:
            tmp = evaluate(arg, env)
            if not isinstance(tmp, Literal) or type(tmp.value) not in (int, float):
                raise Exception("'*' operand must be a number")
            res = res * tmp.value
        return Literal(res)

GLOBALS.register("*", Builtin(interpretFactor))
GLOBALS.register("/", Builtin(interpretFactor, 2))

def interpretNot(symbol, args, env):
    res = evaluate(args[0], env)
    if not isinstance(res, Literal) or res.value not in (True, False):
        raise Exception("'not' only works on booleans")
    return Literal(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, Literal) or cond.value not in (True, False):
        raise Exception("'if' condition must be boolean")
    if cond.value:
        return evaluate(args[1], env)
    elif len(args) == 3:
        return evaluate(args[2], env)
    return None  # 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, Literal) or not isinstance(ev.value, str):
        raise Exception("can only 'print' strings")
    print(ev.value)

    return None  # print returns nothing

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

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

    ev = evaluate(args[1], env)
    env.register(name, ev)
    '''
    if isinstance(ev, UserFunction):
        env.register(name, ev)
    else:
        env.register(name, args[1])
    '''
    return None

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

def interpretRedef(symbol, args, env):
    if not isinstance(args[0], Symbol):
        raise Exception("'redef' requires a string literal as a name")
    name = args[0].name  # NOTE: we are not evaluating the name!!
    if not env.contains(name):
        raise Exception("'redef' only works on previously defined variables")

    ev = evaluate(args[1], env)
    env.reregister(name, ev)
    return None

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):
    return Literal(str(evaluate(args[0], env).value))

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

def interpretConcat(symbol, args, env):
    # concat str1 str2...strN
    if len(args) < 2:
        raise Exception("'concat' takes at least two arguments")
    out = ""
    for arg in args:
        tmp = evaluate(arg, env)
        if not isinstance(tmp, Literal) and not isinstance(tmp.value, str):
            raise Exception("'concat' arguments must be strings")
        out += tmp.value
    return Literal(out)

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

def interpretForCount(symbol, args, env):
    # for-count int exprs
    num = evaluate(args[0], env)
    if not isinstance(num, Literal) or type(num.value) is not int:
        raise Exception("'for-count' count must be an integer")
    new_env = Environment(env)
    ret = None
    for idx in range(0, num.value):
        new_env.register("idx", Literal(idx + 1))
        for arg in args[1:]:
            ret = evaluate(arg, new_env)
    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 Exception("'for-each' expects a list")
    new_env = Environment(env)
    ret = None
    for item in lst.args:
        new_env.register("_item_", item)
        for arg in args[1:]:
            ret = evaluate(arg, new_env)
    return ret

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

def interpretPipe(symbol, args, env):
    if len(args) < 2:
        raise Exception("'|' takes 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)
    return pipe

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

def interpretBranch(symbol, args, env):
    if len(args) == 0:
        raise Exception("'branch' takes at least one expression")
    for arg in args:
        if len(arg.args) != 2:
            raise Exception("'branch' branches have two expressions")
        cond = evaluate(arg.args[0], env)  # this is the condition
        if cond.value:
            return evaluate(arg.args[1], env)
    return None

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

def interpretFunc(symbol, args, env):
    # func <name> (args) (exprs)
    if len(args) < 3:
        raise Exception("'func' takes a name, arguments, and at least one expression")
    if not isinstance(args[0], Symbol):
        raise Exception("'func' requires a string literal as a 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 None

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 Exception(f"no such file: {target_file}")
    with open(target_file, "r") as fil:
        data = fil.readlines()
    out = List([Literal(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)
    return Literal(out.value.strip())

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

#  - string->int and string->float
def interpretStringToInt(symbol, args, env):
    try:
        val = int(args[0].value)
        return Literal(val)
    except:
        raise Exception(f"can't convert {args[0].value} to an int")

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, Literal) or not isinstance(target.value, str):
        raise Exception("'split' expects a string")
    splitter = evaluate(args[1], env)
    if not isinstance(splitter, Literal) or not isinstance(splitter.value, str):
        raise Exception("'split' expects a string as it's splitter")
    return List(target.value.split(splitter.value), True)

GLOBALS.register("split", Builtin(interpretSplit, 2))
    
#  - get the length of a list
def interpretListLength(symbol, args, env):
    ev = evaluate(args[0], env)
    if not isinstance(ev, List):
        raise Exception("'first' expects a List")
    return Literal(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 Exception("'first' expects a List")
    if len(ev.args) == 0:
        raise Exception("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 Exception("'rest' expects a List")
    # 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 Exception("'map' takes a function as its first argument")
    lst = evaluate(args[1], env)
    if not isinstance(lst, List):
        raise Exception("'map' takes a List as its second argument")
    out = []
    for arg in lst.args:
        #arg_ev = evaluate(arg, env)
        ev = evaluate(List([func, arg]), env)
        #ev = evaluate(List([func, arg_ev]), env)
        #out.append(Literal(ev)) # TODO this is probably wrong
        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 Exception("'zip' only works on lists")
    z2 = evaluate(args[1], env)
    if not isinstance(z2, List):
        raise Exception("'zip' only works on lists")
    if len(z1.args) != len(z2.args):
        raise Exception("'zip' expects two lists of the same size")
    out = []
    for idx in range(len(z1.args)):
        #f = z1.args[idx]
        #if not isinstance(f, Literal):
        #    f = evaluate(f, env)
        #s = z2.args[idx]
        #if not isinstance(s, Literal):
        #    s = evaluate(s, env)
        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 Exception("'list-reverse' expects a list")
    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 Exception("'apply' takes a function as its first argument")
    lst = evaluate(args[1], env)
    #lst = args[1]
    if not isinstance(lst, List):
        raise Exception("'apply' takes a List as its second argument")
    new_lst = List([func] + lst.args)
    return evaluate(new_lst, env)

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