nac3-spec/toy-impl/parse_expr.py

import ast
import copy
from helper import *
from type_def import *
from inference import *

# we assume having the following types:
# bool, int32 and float with associated operations

# not handled now: named expression, type guard

def parse_expr(ctx: Context,
               sym_table: dict[str, Type],
               expr: ast.expr):
    if isinstance(expr, ast.Expression):
        body = expr.body
    else:
        body = expr
    if isinstance(body, ast.Constant):
        result = parse_constant(ctx, sym_table, body)
    elif isinstance(body, ast.UnaryOp):
        result = parse_unary_ops(ctx, sym_table, body)
    elif isinstance(body, ast.BinOp):
        result = parse_bin_ops(ctx, sym_table, body)
    elif isinstance(body, ast.Name):
        result = parse_name(ctx, sym_table, body)
    elif isinstance(body, ast.List):
        result = parse_list(ctx, sym_table, body)
    elif isinstance(body, ast.Tuple):
        result = parse_tuple(ctx, sym_table, body)
    elif isinstance(body, ast.Attribute):
        result = parse_attribute(ctx, sym_table, body)
    elif isinstance(body, ast.BoolOp):
        result = parse_bool_ops(ctx, sym_table, body)
    elif isinstance(body, ast.Compare):
        result = parse_compare(ctx, sym_table, body)
    elif isinstance(body, ast.Call):
        result = parse_call(ctx, sym_table, body)
    elif isinstance(body, ast.Subscript):
        result = parse_subscript(ctx, sym_table, body)
    elif isinstance(body, ast.IfExp):
        result = parse_if_expr(ctx, sym_table, body)
    elif isinstance(body, ast.ListComp):
        result = parse_list_comprehension(ctx, sym_table, body)
    else:
        raise CustomError(f'{body} is not yet supported', body)
    body.type = result
    return result

def get_unary_op(op):
    if isinstance(op, ast.UAdd):
        return '__pos__'
    if isinstance(op, ast.USub):
        return '__neg__'
    if isinstance(op, ast.Invert):
        return '__invert__'
    raise Exception(f'Unknown {expr}')

def get_bin_ops(op):
    if isinstance(op, ast.Div):
        return '__truediv__'
    if isinstance(op, ast.BitAnd):
        return '__and__'
    if isinstance(op, ast.BitOr):
        return '__or__'
    if isinstance(op, ast.BitXor):
        return '__xor__'
    return f'__{type(op).__name__.lower()}__'

def parse_constant(ctx: Context,
                   sym_table: dict[str, Type],
                   node):
    v = node.value
    if isinstance(v, bool):
        return ctx.types['bool']
    elif isinstance(v, int):
        return ctx.types['int32']
    elif isinstance(v, float):
        return ctx.types['float']
    else:
        raise CustomError(f'unknown constant {v}', node)

def parse_name(ctx: Context,
               sym_table: dict[str, Type],
               node):
    if node.id in sym_table:
        return sym_table[node.id]
    else:
        raise CustomError(f'unbounded variable {node.id}', node)

def parse_list(ctx: Context,
               sym_table: dict[str, Type],
               node):
    types = [parse_expr(ctx, sym_table, e) for e in node.elts]
    if len(types) == 0:
        return ListType(BotType())
    for t in types[1:]:
        if t != types[0]:
            raise CustomError(f'inhomogeneous list is not allowed', node)
    return ListType(types[0])

def parse_tuple(ctx: Context,
                sym_table: dict[str, Type],
                node):
    types = [parse_expr(ctx, sym_table, e) for e in node.elts]
    return TupleType(types)

def parse_attribute(ctx: Context,
                    sym_table: dict[str, Type],
                    node):
    obj = parse_expr(ctx, sym_table, node.value)

    if isinstance(obj, TypeVariable) and len(obj.constraints) > 0:
        if node.attr not in obj.constraints[0].fields:
            raise CustomError(f'unknown field {node.attr} in {obj}', node)
        ty = obj.constraints[0].fields[node.attr]
        for v in obj.constraints[1:]:
            if node.attr not in v.fields:
                raise CustomError(f'unknown field {node.attr} in {obj}', node)
            if v.fields[node.attr] != ty:
                raise CustomError(
                    f'unknown field {node.attr} in {obj} (type mismatch)', node)
        return ty

    if node.attr in obj.fields:
        return obj.fields[node.attr]
    raise CustomError(f'unknown field {node.attr} in {obj}', node)

def parse_bool_ops(ctx: Context,
                   sym_table: dict[str, Type],
                   node):
    assert len(node.values) == 2
    left = parse_expr(ctx, sym_table, node.values[0])
    right = parse_expr(ctx, sym_table, node.values[1])
    b = ctx.types['bool']
    if left != b or right != b:
        raise CustomError('operands of bool ops must be booleans', node)
    return b

def parse_bin_ops(ctx: Context,
                  sym_table: dict[str, Type],
                  node):
    left = parse_expr(ctx, sym_table, node.left)
    right = parse_expr(ctx, sym_table, node.right)
    op = get_bin_ops(node.op)
    try:
        return resolve_call(left, op, [right], {}, ctx)
    except CustomError as e:
        raise e.at(node)

def parse_unary_ops(ctx: Context,
                    sym_table: dict[str, Type],
                    node):
    t = parse_expr(ctx, sym_table, node.operand)
    if isinstance(node.op, ast.Not):
        b = ctx.types['bool']
        if t != b:
            raise CustomError('operands of bool ops must be booleans', node)
        return b
    try:
        return resolve_call(t, get_unary_op(node.op), [], {}, ctx)
    except CustomError as e:
        raise e.at(node)

def parse_compare(ctx: Context,
                  sym_table: dict[str, Type],
                  node):
    items = [parse_expr(ctx, sym_table, v) for v in node.comparators]
    items.insert(0, parse_expr(ctx, sym_table, node.left))
    boolean = ctx.types['bool']
    ops = [get_bin_ops(v) for v in node.ops]
    for a, b, op in zip(items[:-1], items[1:], ops):
        try:
            result = resolve_call(a, op, [b], {}, ctx)
            if result != boolean:
                raise CustomError(
                    f'result of comparison must be bool instead of {result}')
        except CustomError as e:
            raise e.at(node)

    return boolean

def parse_call(ctx: Context,
               sym_table: dict[str, Type],
               node):
    if len(node.keywords) > 0:
        raise CustomError('keyword arguments are not supported', node)
    args = [parse_expr(ctx, sym_table, v) for v in node.args]
    obj = None
    f = None
    if isinstance(node.func, ast.Attribute):
        obj = parse_expr(ctx, sym_table, node.func.value)
        f = node.func.attr
    elif isinstance(node.func, ast.Name):
        f = node.func.id
    try:
        return resolve_call(obj, f, args, {}, ctx)
    except CustomError as e:
        raise e.at(node)

def parse_subscript(ctx: Context,
                    sym_table: dict[str, Type],
                    node):
    value = parse_expr(ctx, sym_table, node.value)
    if not isinstance(value, ListType):
        raise CustomError(f'cannot take index of {value}', node)
    i32 = ctx.types['int32']
    if isinstance(node.slice, ast.Slice):
        if node.slice.lower is not None:
            if parse_expr(ctx, sym_table, node.slice.lower) != i32:
                raise CustomError(f'slice index must be int32', node.slice.lower)
        if node.slice.upper is not None:
            if parse_expr(ctx, sym_table, node.slice.upper) != i32:
                raise CustomError(f'slice index must be int32', node.slice.upper)
        if node.slice.step is not None:
            if parse_expr(ctx, sym_table, node.slice.step) != i32:
                raise CustomError(f'slice index must be int32', node.slice.step)
        return value
    else:
        s = parse_expr(ctx, sym_table, node.slice)
        if s == i32:
            return value.params[0]
        else:
            raise CustomError(f'index of type {s} is not supported', node)

def parse_if_expr(ctx: Context,
                  sym_table: dict[str, Type],
                  node):
    b = ctx.types['bool']
    t = parse_expr(ctx, sym_table, node.test)
    if t != b:
        raise CustomError(f'type of conditional must be bool instead of {t}', node)
    ty1 = parse_expr(ctx, sym_table, node.body)
    ty2 = parse_expr(ctx, sym_table, node.orelse)
    if ty1 != ty2:
        raise CustomError(f'divergent type for if expression: {ty1} != {ty2}', node)
    return ty1

def parse_simple_binding(name, ty):
    if isinstance(name, ast.Name):
        if name.id == '_':
            return {}
        name.type = ty
        return {name.id: ty}
    elif isinstance(name, ast.Tuple):
        if not isinstance(ty, TupleType):
            raise CustomError(f'cannot pattern match over {ty}')
        if len(name.elts) != len(ty.params):
            raise CustomError(f'pattern matching length mismatch')
        result = {}
        for x, y in zip(name.elts, ty.params):
            binding = parse_simple_binding(x, y)
            expected = len(result) + len(binding)
            result |= parse_simple_binding(x, y)
            if len(result) != expected:
                raise CustomError('variable name clash', x)
        return result
    else:
        raise CustomError(f'binding to {name} is not supported')

def parse_list_comprehension(ctx: Context,
                             sym_table: dict[str, Type],
                             node):
    if len(node.generators) != 1:
        raise CustomError(
            'list comprehension with more than 1 for loop is not supported', node)
    if node.generators[0].is_async:
        raise CustomError('async list comprehension is not supported', node)
    ty = parse_expr(ctx, sym_table, node.generators[0].iter)
    if isinstance(ty, TypeVariable) and \
            len(ty.constraints) == 1:
        ty = ty.constraints[0]
    if not isinstance(ty, ListType):
        raise CustomError(f'unable to iterate over {ty}', node)
    try:
        sym_table2 = sym_table | parse_simple_binding(node.generators[0].target, ty.params[0])
    except CustomError as e:
        raise e.at(node)
    b = ctx.types['bool']
    for c in node.generators[0].ifs:
        if parse_expr(ctx, sym_table2, c) != b:
            raise CustomError(f'condition should be of boolean type', c)
    return ListType(parse_expr(ctx, sym_table2, node.elt))