String's print, show, and read

Prelude> print "hello"
"hello"
Prelude> show "hello"
"\"hello\""
Prelude> read "hello" :: String
"*** Exception: Prelude.read: no parse
Prelude> read "\"hello\"" :: String
"hello"

Why do print and show for String add double quotes? And why does read have the corresponding expectation?

In other words, why don't they just stick to the verbatim string content?

Supppose they did. Then consider what would happen to (String, String) values, for example:

• ("" , ",,")
• ("," , ",")
• (",," , "")

They would all be printed as

(,,,)

Now if you used read to parse it back, which answer should you get? Or if you saw that in a debugging log message, what should it mean?

Similarly consider what would happen to user-defined types like this:

data D = Dof String String deriving (Read, Show)

Then what would happen to D values such as:

• Dof "" "abc def"
• Dof "abc" "def"
• Dof "abc def" ""

They would all be printed as

Dof abc def

Now if you used read to parse it back, which answer should you get? Or if you saw that in a debugging log message, what should it mean?

Conclusion: The verbatim way is anti-compositional, aka “not a team player”. We need a disambiguating, delimiting notation.

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