[Haskell-cafe] Problem with JHC

[Thomas DuBuisson]

Like paolino, I did a couple tests and found:

> data TreeX = Leaf Int | NotLeaf Int deriving (Show, Read)

    [tommd at Mavlo Test]$ ./jtree
    Give me a tree:
    Leaf 5

    jtree_code.c:2572: case fell off
    Aborted
    [tommd at Mavlo Test]$ ./jtree
    Give me a tree:
    NotLeaf

    jtree_code.c:2572: case fell off
    Aborted


So the read for that does not work... but surprisingly...

> data TreeX = Leaf Int | NotLeaf deriving (Show, Read)

Dropping the Int from the second constructor works (ignore the
constructor names, they are just place-holders).

    [tommd at Mavlo Test]$ ./jtree
    Give me a tree:
    Leaf 43
    Leaf 43
    [tommd at Mavlo Test]$ ./jtree
    Give me a tree:
    NotLeaf
    NotLeaf


--- OTHER TESTS ---
1) data TreeX = Leaf | NotLeaf 5 deriving (Show, Read)
Another unfortunate bug is that reversing the constructors (having
Leaf as a nullary constructor and NotLeaf taking an Int) causes
compilation to fail (using jhc-0.7.2-0).

2) data TreeX = Leaf Int | NotLeaf Int | OoopsLeaf deriving (Show, Read)

Works fine - notice it ends with a nullary constructor...
Hypothesis 1: All working Read derivations have data declarations with
a nullary constructor at the end.

3) data TreeX = Leaf Int | NotLeaf | OoopsLeaf Int deriving (Show, Read)

Fails in with 'case fell off', so H1 seems good

4) data TreeX = Leaf Int | NotLeaf | OoopsLeaf deriving (Show, Read)
Works.

5) data TreeX = Leaf | NotLeaf | OoopsLeaf Int deriving (Show, Read)

Fails to compile.  Hypothesis 2: All working Read derivations that
don't cause compile issues have data declarations with non-nullary
first constructors.

Cheers,
Thomas