Add list.pop

[kabra1110]

Closes #1821.

---

Issues

1. Currently does not work with structures like list[tuple[i32, i32]]. Looks like the function is called twice (?)

from lpython import i32

def list_pop():
    l: list[tuple[i32, i32]]
    l = [(1,2)]
    print(l.pop())
    print(l)

list_pop()

(1, IndexError: pop from empty list

This IndexError is output when trying to pop empty lists (as in CPython).

2. For now, supported only as expression or statement. The first commit supports statement x.pop() by wrapping IntrinsicFunction into Expr, while the second supports expression (so print(x.pop()) works, for example).

[czgdp1807]

We will investigate the bug you are facing on Saturday.

[czgdp1807]

Also add a verify_args and register it in the appropriate place. Try to see the pattern of other verify_args.

[czgdp1807]

The problem is with print_list_tuple ASR pass. It transforms print(l.pop()) into print(l.pop()[0], l.pop()[1]) which calls l.pop twice leading to the error because in second call to l.pop() the list is empty. The correct transformation would be t = l.pop(); print(t).

[czgdp1807]

Use the following test case,

from lpython import i32

def list_pop():
    l: list[tuple[i32, i32]]
    t: tuple[i32, i32]
    l = [(-4, 2)]
    t = l.pop()
    print(t)
    print(l)

list_pop()

[czgdp1807]

For making the following work, just create the node for list.pop and then wrap it up inside Expr if its created inside AST::Expr.

from lpython import i32

def list_pop():
    l: list[tuple[i32, i32]
    l = [(-4, 2)]
    l.pop()
    print(l)

list_pop()

[czgdp1807]

Suggested change

	// static ASR::asr_t* eval_list_pop(ASR::expr_t *s, Allocator &al, const Location &loc,
	// Vec<ASR::expr_t*> &args, diag::Diagnostics &diag) {
	// if (args.size() > 1) {
	// throw SemanticError("pop() takes atmost one argument",
	// loc);
	// }
	// ASR::expr_t *idx = nullptr;
	// ASR::ttype_t *int_type = ASRUtils::TYPE(ASR::make_Integer_t(al, loc,
	// 4, nullptr, 0));
	// ASR::ttype_t *type = ASRUtils::expr_type(s);
	// ASR::ttype_t *list_type = ASR::down_cast<ASR::List_t>(type)->m_type;
	// if (args.size() == 1) {
	// ASR::ttype_t *pos_type = ASRUtils::expr_type(args[0]);
	// if (!ASRUtils::check_equal_type(pos_type, int_type)) {
	// std::string fnd = ASRUtils::type_to_str_python(pos_type);
	// std::string org = ASRUtils::type_to_str_python(int_type);
	// diag.add(diag::Diagnostic(
	// "Type mismatch in 'pop', List index should be of integer type",
	// diag::Level::Error, diag::Stage::Semantic, {
	// diag::Label("type mismatch (found: '" + fnd + "', expected: '" + org + "')",
	// {args[0]->base.loc})
	// })
	// );
	// throw SemanticAbort();
	// }
	// idx = args[0];
	// } else {
	// // default is last index
	// idx = (ASR::expr_t*)ASR::make_IntegerConstant_t(al, loc, -1, int_type);
	// }
	// return make_ListPop_t(al, loc, s, idx, list_type, nullptr);
	// }

[czgdp1807]

These errors weren't there before. I would like to go back to the original errors. pop should take arguments and work with them.

[kabra1110]

Added a commit to allow pop with position argument. Does not seem to work correctly with nested iterables.

from lpython import i32, f64

def test_list_pop():
    l1: list[tuple[i32, f64]]
    x: tuple[i32, f64]

    l1 = [(1, 1.0), (2, 4.0)]
    x = l1.pop(0)
    print(x)        # incorrect
    print(l1)       # correct

test_list_pop()

(2, 4.00000000000000000e+00)
[(2, 4.00000000000000000e+00)]

Also, errors correctly caught in verify_args lead to an LCompilersException. It does not seem related to this specific PR, though.

[czgdp1807]

Insert the following as a test case,

from lpython import i32, f64, InOut

def pop_wrapper(l: InOut[list[tuple[i32, f64]]], idx: i32) -> tuple[i32, f64]:
    return l.pop(idx)

def test_list_pop():
    l1: list[tuple[i32, f64]]
    x: tuple[i32, f64]
    i: i32

    l1 = [(1, 1.0), (2, 4.0), (3, 6.0)]

    x = pop_wrapper(l1, 0)
    print(x)
    assert x == (1, 1.0)

    l1.append((4, 8.0))
    assert x == (1, 1.0)

    print(l1)
    for i in range(len(l1)):
        assert l1[i] == (i + 2, 2.0*f64(i + 2))

test_list_pop()

[czgdp1807]

Rest LGTM.