unison/unison-src/transcripts/fix1800.md

```ucm:hide
scratch/main> builtins.merge
```

```unison:hide
printLine : Text ->{IO} ()
printLine msg =
  _ = putBytes.impl (stdHandle StdOut) (Text.toUtf8 (msg ++ "\n"))
  ()

-- An unannotated main function
main1 = '(printLine "\nhello world!")

-- Another variation
main2 _ = printLine "🌹"

-- An annotated main function
main3 : '{IO} ()
main3 _ = printLine "🦄 ☁️  🌈"
```

Testing a few variations here:

* Should be able to run annotated and unannotated main functions in the current file.
* Should be able to run annotated and unannotated main functions from the codebase.

```ucm
scratch/main> run main1
scratch/main> run main2
scratch/main> run main3
scratch/main> add
scratch/main> rename.term main1 code.main1
scratch/main> rename.term main2 code.main2
scratch/main> rename.term main3 code.main3
```

The renaming just ensures that when running `code.main1`, it has to get that main from the codebase rather than the scratch file:

```ucm
scratch/main> run code.main1
scratch/main> run code.main2
scratch/main> run code.main3
```

Now testing a few variations that should NOT typecheck.

```unison:hide
main4 : Nat ->{IO} Nat
main4 n = n

main5 : Nat ->{IO} ()
main5 _ = ()
```

This shouldn't work since `main4` and `main5` don't have the right type.

```ucm:error
scratch/main> run main4
```

```ucm:error
scratch/main> run main5
```