[MLton] confusing error message from MLton
Mon, 21 Jun 2004 14:52:52 -0400 (EDT)
> The error is
> 14.29: syntax error: inserting VAL
> which certainly confused me. I would have expected first to get the error
> about fiba referring to fibb (because the third `fun' should be `and').
MLton does _all_ lexing and parsing before any elaboration. So, you won't
see any unbound identifiers or type-checking errors if there are any
syntactic errors in the program.
> I would expect it would have either complained about `def' being unbound or
> else about no `fun' before `def'.
Presumably, the attempt to insert a VAL arises from the use of =.
But, I don't know why the grammer isn't parsing the code with = as an
infix. It seems like the following would be a valid parse:
fun fibb x =
if x <= 1
else fiba (x - 1) + (( fiba (x - 2)
def doOne arg )) = ((
case Int.fromString arg of
SOME arg' =>
(print (arg ^ " => ");
print (Int.toString (fib arg') ^ "\n"))
| _ =>
print ("\"" ^ String.toString arg ^ "\" is not an integer\n") ))
That is, parse the equals as infix, applied to fiba applied to 4 arguments
and to the case expression.