pizza pipe not working

[Anton-4]

Error message:

$ roc check temp.roc
── TOO FEW ARGS in temp.roc ────────────────────────────────────────────────────

The first function expects 1 argument, but it got only 0:

4│      ["hello"] |> List.first()?
                     ^^^^^^^^^^

Roc does not allow functions to be partially applied. Use a closure to
make partial application explicit.

────────────────────────────────────────────────────────────────────────────────

1 error and 0 warnings found in 13 ms.

module [something]

something = |_|
    ["hello"] |> List.first()?

This version does work:

module [something]

something = |_|
    ["hello"] |> List.first()

If we look at the desugared version we'll probably be able to make sense of this.

• We should add a test for this failure once fixed.

[Anton-4]

Link to zulip discussion: https://roc.zulipchat.com/#narrow/channel/463736-bugs/topic/too.20few.20args/near/494452838

[Anton-4]

The desugared version of

module [something]

something = |_|
    ["hello"] |> List.first()?

Is:

Body(
            @20-29 Identifier {
                ident: "something",
            },
            @32-66 Closure(
                [
                    @33-34 Underscore(
                        "",
                    ),
                ],
                @40-65 LowLevelTry(
                    @40-65 Apply(
                        @53-65 PncApply(
                            @53-63 Var {
                                module_name: "List",
                                ident: "first",
                            },
                            [],
                        ),
                        [
                            @40-49 List(
                                [
                                    @41-48 Str(
                                        PlainLine(
                                            "hello",
                                        ),
                                    ),
                                ],
                            ),
                        ],
                        Try,
                    ),
                    OperatorSuffix,
                ),
            ),
        )

The desugared version of:

module [something]

something = |_|
    ["hello"] |> List.first()

Is:

Body(
            @20-29 Identifier {
                ident: "something",
            },
            @32-65 Closure(
                [
                    @33-34 Underscore(
                        "",
                    ),
                ],
                @40-65 Apply(
                    @53-63 Var {
                        module_name: "List",
                        ident: "first",
                    },
                    [
                        @40-49 List(
                            [
                                @41-48 Str(
                                    PlainLine(
                                        "hello",
                                    ),
                                ),
                            ],
                        ),
                    ],
                    BinOp(
                        Pizza,
                    ),
                ),
            ),
        )

[Anton-4]

Recommended workaround:
Change

module [something]

something = |_|
    ["hello"] |> List.first()?

To:

module [something]

something = |_|
    List.first(["hello"])

[Anton-4]

Desugaring was changed in #7548
Full explanation in https://roc.zulipchat.com/#narrow/channel/463736-bugs/topic/too.20few.20args/near/495870357