On Wednesday, July 3, 2019 at 3:03:20 AM UTC+2, Gert wrote:
>
> https://github.com/golang/go/blob/master/src/errors/wrap.go
>
> What if we replaced all error types in that file with a empty interface or
> a general monad interface? Can we make it work for other types too and
> introduce a new monad package instead a new error package only?
>
>
```
package monad
type Monad interface {
Unwrap() Monad
}
func Unwrap(m Monad) Monad {
if m != nil {
return m.Unwrap()
}
return nil
}
```
```
package monad_test
import (
"monad"
"testing"
)
type monadT struct{ s string }
func (m monadT) Unwrap() monad.Monad { return nil }
type wrappedT struct {
s string
m monad.Monad
}
func (w wrappedT) Unwrap() monad.Monad { return w.m }
func TestUnwrap(t *testing.T) {
m1 := monadT{"monad"}
m2 := wrappedT{"monad wrap", m1}
testCases := []struct {
m monad.Monad
want monad.Monad
}{
{nil, nil},
{wrappedT{"wrapped", nil}, nil},
{m1, nil},
{m2, m1},
{wrappedT{"wrap 3", m2}, m2},
}
for _, tc := range testCases {
if got := monad.Unwrap(tc.m); got != tc.want {
t.Errorf("Unwrap(%v) = %v, want %v", tc.m, got, tc.want)
}
}
}
```
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