Hi
I've found the bugs in read and show that stop (read . show) from
working.
This is in hugs 1.4, the November 1998 beta.
They occur when showing data types with record syntax.
There are two bugs:
1 readField in the prelude should be as follows:
readField :: Read a => String -> ReadS a
readField m s0 = [ r | (t, s1) <- lex s0, t == m,
("=",s2) <- lex s1,
r <- reads s2 ] *** instead of readsPrec
10
this makes it consistent with showField
showField :: Show a => String -> a -> ShowS
showField m v = showString m . showChar '=' . shows v
2 constructors with record syntax when printed should be bracketed:
That is, in static.c the code for showing record syntax should be as
follows.
(changed lines are marked with a ***).
This makes it consistent with reading record syntax.
/* To display a value using record syntax:
* showParen (d>=10) ***
* (showsPrec d C{x=e, y=f, z=g} = showString "C" . showChar
'{' .
* showField "x" e . showChar ',' .
* showField "y" f . showChar ',' .
* showField "z" g . showChar '}')
* showField lab val
* = showString lab . showChar '=' . shows val
*/
Cell rhs = showsCB;
List vs = dupOnto(snd(hd(cfs)),NIL);
if (isAp(pat)) {
for (;;) {
rhs = ap2(nameComp,
ap2(nameShowField,
mkStr(textOf(hd(vs))),
arg(pat)),
rhs);
pat = fun(pat);
vs = tl(vs);
if (isAp(pat))
rhs = ap(showsCM,rhs);
else
break;
}
}
rhs = ap2(nameComp,ap(nameApp,mkStr(name(h).text)),ap(showsOB,rhs));
rhs = ap2(nameShowParen,ap2(nameLe,mkInt(10),d),rhs); ***
return rhs;
--
Meurig Sage
Dept of Computing Science
University of Glasgow
http://www.dcs.gla.ac.uk/~meurig
mailto:[EMAIL PROTECTED]
