# E0027

Warning name: `deprecated_syntax`

The syntax is deprecated. Please refer to the warning message on the reason and
potential fix.

For example, one deprecated usage is declaring a polymorphic function as
`fn f[T]`. Instead, write the type parameters before the function name, as in
`fn[T] f`.

## Erroneous example

```{literalinclude} /sources/error_codes/0027_error/top.mbt
:language: moonbit
```

## Suggestion

Migrate the code according to the warning message. In this case, move the type
parameter list before the function name.

```{literalinclude} /sources/error_codes/0027_fixed/top.mbt
:language: moonbit
```