unison/unison-src/transcripts-using-base/utf8.md

Test for new Text -> Bytes conversions explicitly using UTF-8 as the encoding

Unison has function for converting between Text and a UTF-8 Bytes encoding of the Text.

scratch/main> find Utf8

ascii characters are encoded as single bytes (in the range 0-127).

ascii: Text
ascii = "ABCDE"

> toUtf8 ascii

non-ascii characters are encoded as multiple bytes.

greek: Text
greek = "ΑΒΓΔΕ"

> toUtf8 greek

We can check that encoding and then decoding should give us back the same Text we started with

checkRoundTrip: Text -> [Result]
checkRoundTrip t =
  bytes = toUtf8 t
  match fromUtf8.impl bytes with
    Left e -> [Result.Fail "could not decode"]
    Right t' -> if t == t' then [Result.Ok "Passed"] else [Result.Fail ("Got: " ++ t' ++ " Expected: " ++ t)]

greek = "ΑΒΓΔΕ"

test> greekTest = checkRoundTrip greek

If we try to decode an invalid set of bytes, we get back Text explaining the decoding error:

greek_bytes = Bytes.fromList [206, 145, 206, 146, 206, 147, 206, 148, 206]


-- Its an error if we drop the first byte
> match fromUtf8.impl (drop 1 greek_bytes) with
  Left (Failure _ t _) -> t
  _ -> bug "expected a left"