Bill Page <[email protected]> writes:
| On Mon, Oct 24, 2011 at 7:36 PM, Gabriel Dos Reis wrote:
| > ...
| > Bill Page writes:
| > | So it is a coincidence that the compiler happens to choose 0@P or that
| > | the representation of all of these candidates is the same so that it
| > | does not matter?
| >
| > It is mostly concidence. The explanation is that the type of leftLcm is
| >
| >
| > (P,P) -> P
| >
| > and before starting the compilation of a function body, the compiler
| > automatically imports the return type and domain of each parameter.
| > So the modemap of 0@P happens to be first on the list, and since the
| > compilers the first that makes tentative compilation OK, it picks it and
| > moves on.
| >
|
| So here it seems very clear that one should have written:
|
| v:P := 0
|
| and the use of
|
| v := 0
|
| should produce an error message. I retrospect I think I have probably
| been bitten by this bug a few times in the past. One just seems to get
| used to working around such limitations. But this seems like an
| improvement to me even if it does affect a lot of existing code that
| happens to work right now. A sensible error message would be welcome.
| Would this be hard to do?
1. The error message I have is:
compiling exported leftLcm : (P,P) -> P
****** comp fails at level 5 with expression: ******
error in function leftLcm
(IF (= |a| 0)
|b|
(IF (= |b| 0)
|a|
(SEQ (|:=| |b0| |b|) (|:=| |u| ((|elt| P |monomial|) 1 0)) (|:=| |v| 0)
(REPEAT (WHILE (~= (|leadingCoefficient| |b|) 0))
(SEQ (|:=| |qr| (|leftDivide| |a| |b|))
(|:=| (|%Comma| |a| |b|)
(|%Comma| |b| (|qr| |remainder|)))
(|exit| 1
(|:=| (|%Comma| |u| |v|)
(|%Comma| (+ (* |u| (|qr| |quotient|)) |v|)
|u|)))))
(|exit| 1 (* |b0| |u|)))))
****** level 5 ******
$x:= (Zero)
$m:= $EmptyMode
$f:=
((((|u| #) (|b0| #) (|b| # #) (|a| # #) ...)))
>> Apparent user error:
Ambiguous constant 0 in ? constext. Candidates are
0: P
0: F
0: NonNegativeInteger
0: Integer
2. In fact, I don't have to change that many existing codes. However,
for a few cases, it takes a while to figure out what the right answer
should be. Which convinces me that the tightening is the right thing to do.
So far, I've posted mostly the easier ones.
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