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last edited 16 years ago by gdr |
Edit detail for #378 Declarations with multiple variables don't work inside of functions revision 2 of 3
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Editor: gdr
Time: 2008/02/22 10:02:28 GMT-8 |
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| Note: the comma syntax stands for tuple construction | ||
added:
From gdr Fri Feb 22 10:02:24 -0800 2008
From: gdr
Date: Fri, 22 Feb 2008 10:02:24 -0800
Subject: the comma syntax stands for tuple construction
Message-ID: <20080222100224-0800@axiom-wiki.newsynthesis.org>
It seems that a comma separated list is a tuple, therefore
\begin{axiom}
c,d: POLY INT
\end{axiom}
is a tuple, consisting of a symbol `c' and a
declaration `d: POLY INT'. However, a declaration
has type `Void', and since a Tuple is a homogeneous
container, both component must be brought to a
common type, which is `Void'. Thus we get a Tuple Void.
But, a `Void' is not coercible to OutputForm, therefore
we get the LISP output. Try
\begin{axiom}
2,3
\end{axiom}
The syntax for declarations which have multiple variables is given on page 142 of the Axiom book. However, using this syntax inside a function results in the compiler failing.
The first time an attempt is made to compile a function which uses this syntax, no diagnostic is produced. However, the libraries needed by the function being compiled are not loaded, and the function itself is not executed (or at least it doesn't produce any output). If a second attempt is made to execute the function, a "System error" results.
The following session transcript demonstrates the problem. It attempts to execute two functions. The first of these, named "bug", demonstrates the behavior described above. The second function, named "nonbug", is identical to "bug" except that the declaration containing two variables has been replaced by two declarations each containing a single variable. Axiom handles the "nonbug" function correctly, demonstrating that the problem is triggered by a declaration containing multiple variables. The transcript follows:
$ axiom
AXIOM Computer Algebra System
Version: Axiom (April 2006)
Timestamp: Wednesday June 21, 2006 at 03:45:56
-----------------------------------------------------------------------------
Issue )copyright to view copyright notices.
Issue )summary for a summary of useful system commands.
Issue )quit to leave AXIOM and return to shell.
----------------------------------------------------------------------------- Re-reading compress.daase Re-reading interp.daase
Re-reading operation.daase
Re-reading category.daase
Re-reading browse.daase
(1) ->
(1) -> bug(x) == (local a, b; (a, b) : Integer; 1)
Type: Void
(2) -> bug(1)
Compiling function bug with type PositiveInteger -> PositiveInteger
(2) -> bug(1)
>> System error:
(|Tuple| |a| |b|) is not of type SYMBOL.
(2) -> nonbug(x) == (local c, d; c : Integer; d : Integer; 1)
Type: Void
(3) -> nonbug(1)
Compiling function nonbug with type PositiveInteger ->
PositiveInteger
Loading /home/ka/w/axiom/mnt/linux/algebra/PI.o for domain
PositiveInteger
Loading /home/ka/w/axiom/mnt/linux/algebra/NNI.o for domain
NonNegativeInteger
Loading /home/ka/w/axiom/mnt/linux/algebra/INT.o for domain Integer
Loading /home/ka/w/axiom/mnt/linux/algebra/OUTFORM.o for domain
OutputForm
Loading /home/ka/w/axiom/mnt/linux/algebra/LIST.o for domain List
(3) 1
Type: PositiveInteger
(4) -> )quit
axiomnobug(x) == (local a, b; a, b : Integer; a:=b:=1; a+b)
axiomnobug(1)
Compiling function nobug with type PositiveInteger -> Integer
 | (1) |
axiombug(x) == (local a, b; (a, b) : Tuple Integer; a:=b:=1; a+b)
axiombug(1) Cannot convert right-hand side of assignment 1 to an object of the type Tuple Integer of the left-hand side.
Also, when I tried this in my Windows version, I got:
AXIOM Computer Algebra System
Version of Tuesday November 30, 2004 at 21:11:14
-----------------------------------------------------------------------------
Issue )copyright to view copyright notices.
Issue )summary for a summary of useful system commands.
Issue )quit to leave AXIOM and return to shell.
-----------------------------------------------------------------------------
(1) -> bug(x) == (local a, b; (a, b) : Integer; 1)
Type: Void
(2) -> bug(1)
Compiling function bug with type PositiveInteger -> PositiveInteger
>> System error:
(|Tuple| |a| |b|) is not of type SYMBOL.
protected-symbol-warn called with (NIL)
So the older version caught the syntax error on first compile and run. Your example seems to me to be a syntax error that was not caught in the current version on first compile and run (I was not able to find the (a,b):Integer in the Axiom book.) since (a,b) is a tuple. Correct syntax is a, b:Integer for multivariable declarations. Note that (a,b):Tuple Integer is incorrect syntax also, since (a,b) is not an indentifier.
(a,b):Type is syntactic sugar in the interpreter and a,b:Type does not define type of a correctly (but b is typed correctly; probably the reason to require parenthesis---this requires the interpreter parser to distinguish (a,b) to the left of : from to the right of : ). So this is another inconsistency between interpreter and compiler, or this may be due to an original bug or an unknown difficulty in parsing the comma separator in the interpreter. Alternatively, if the compiler manual says (a,b):Type should be okay, then it is a compiler bug and the workaround is to use a,b:Type.
axiom(a,b):POLY INT
axioma:= 11
 | (2) |
axiomtypeOf a
 | (3) |
axiomb:= 12
 | (4) |
axioma+b
 | (5) |
axiomc,d:POLY INT LISP output: (() ())
axiomc:=11
 | (6) |
axiomd:=12
 | (7) |
axiomc+d
 | (8) |
Why does c,d:POLY INT produce a Lisp output? and of type Tuple Void?
axiomc,d: POLY INT LISP output: (() ())
is a tuple, consisting of a symbol `c' and a declaration `d: POLY INT'. However, a declaration has type `Void', and since a Tuple is a homogeneous container, both component must be brought to a common type, which is `Void'. Thus we get a Tuple Void. But, a `Void' is not coercible to OutputForm?, therefore we get the LISP output. Try
axiom2,3
 | (1) |