Stream: beginners

Topic: How to import modules?

Aurélien Geron (Jun 08 2026 at 01:01):

I'm confused about the imports.

I have a FooBar.roc file containing this code:

FooBar :: {}.{
    square : a -> a
    square = |x| { x * x }

    cube : a -> a
    cube = |x| { x * x * x }
}

And I have this test.roc file:

import FooBar exposing [square]

main! = |_arg| {
    res = square(12)
    echo!(res.to_str())
    Ok({})
}

When I run test.roc, I get this error:

-- MODULE NOT FOUND ------------------------------

The module FooBar was not found in this Roc project.

You're attempting to use this module here:
  ┌─ /var/folders/74/7_g_vgn57nzgjh9mw5smp6rc0000gn/T/roc/debug-e8a08c1b/eA0BPcpNGwkobyfgh8wRPMuhj8Oc4veQ/main.roc:7:1
  │
7 │ import FooBar exposing [square]
  │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

-- UNDEFINED VARIABLE ----------------------------

Nothing is named square in this scope.
Is there an import or exposing missing up-top?

   ┌─ /var/folders/74/7_g_vgn57nzgjh9mw5smp6rc0000gn/T/roc/debug-e8a08c1b/eA0BPcpNGwkobyfgh8wRPMuhj8Oc4veQ/main.roc:10:11
   │
10 │     res = square(12)
   │           ^^^^^^

-- FILE NOT FOUND --------------------------------

/var/folders/74/7_g_vgn57nzgjh9mw5smp6rc0000gn/T/roc/debug-e8a08c1b/eA0BPcpNGwkobyfgh8wRPMuhj8Oc4veQ/FooBar.roc: FileNotFound


Found 3 error(s) and 0 warning(s) for /var/folders/74/7_g_vgn57nzgjh9mw5smp6rc0000gn/T/roc/debug-e8a08c1b/eA0BPcpNGwkobyfgh8wRPMuhj8Oc4veQ/main.roc.

I'm not sure what I did wrong. Any help would be greatly appreciated.

Richard Feldman (Jun 08 2026 at 01:23):

taking a look!

Richard Feldman (Jun 08 2026 at 01:41):

ok it turns out that @Aurélien Geron you're the first person to attempt importing modules in the new "default app" (with no platform) :joy:

Richard Feldman (Jun 08 2026 at 01:41):

they work when you have a platform but there's a bug that breaks importing for default apps - I'll have a fix soon

Aurélien Geron (Jun 08 2026 at 02:08):

Oh cool, thanks @Richard Feldman!
I know it's early, but I've started looking at porting the Exercism Roc track to the new compiler. I don't expect it to be very hard overall, but many exercises depend on external modules, especially unicode, so those exercises at least will have to wait.

Aurélien Geron (Jun 08 2026 at 03:10):

I just tested the code with a platform, and indeed it works just fine. :+1:

Note that I tried the following import, but it didn't compile (it said that square wasn't exposed):

import FooBar exposing [square]

I had to use this workaround:

import FooBar
square = FooBar.square

Is this working as intended?

Also, I had to replace a -> a with I64 -> I64 or else the compiler complained that x does not have a times method. I thought that Roc didn't force me to be precise in the type signatures?

Richard Feldman (Jun 08 2026 at 03:40):

yeah I found an unrelated exposing bug too - this PR addresses both!

Last updated: Jun 16 2026 at 16:19 UTC