nac3-spec/toy-impl/parse_expr.py

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

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

# not handled now: slice, comprehensions, named expression, if 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):
        return parse_constant(ctx, sym_table, body)
    if isinstance(body, ast.UnaryOp):
        return parse_unary_op(ctx, sym_table, body)
    if isinstance(body, ast.BinOp):
        return parse_bin_ops(ctx, sym_table, body)
    if isinstance(body, ast.Name):
        return parse_name(ctx, sym_table, body)
    if isinstance(body, ast.List):
        return parse_list(ctx, sym_table, body)
    if isinstance(body, ast.Tuple):
        return parse_tuple(ctx, sym_table, body)
    if isinstance(body, ast.Attribute):
        return parse_attribute(ctx, sym_table, body)
    if isinstance(body, ast.BoolOp):
        return parse_bool_ops(ctx, sym_table, body)
    if isinstance(body, ast.Compare):
        return parse_compare(ctx, sym_table, body)
    if isinstance(body, ast.Call):
        return parse_call(ctx, sym_table, body)
    if isinstance(body, ast.Subscript):
        return parse_subscript(ctx, sym_table, body)
    raise CustomError(f'{body} is not yet supported')


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, int):
        return ctx.types['int32']
    elif isinstance(v, bool):
        return ctx.types['bool']
    else:
        raise CustomError(f'unknown constant {v}')

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}')

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

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')
    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)
    return resolve_call(left, op, [right], {}, ctx)

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

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):
        result = resolve_call(a, op, [b], {}, ctx)
        if result != boolean:
            raise CustomError(
                f'result of comparison must be bool instead of {result}')
    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')
    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(node.func.value)
        f = node.func.attr
    elif isinstance(node.func, ast.Name):
        f = node.func.id
    return resolve_call(obj, f, args, {}, ctx)

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}')
    s = parse_expr(ctx, sym_table, node.slice)
    i32 = ctx.types['int32']
    if s == i32:
        return value.params[0]
    else:
        # will support slice
        raise CustomError(f'index of type {s} is not supported')