Date: Thu, 8 Feb 2001 14:31:05 -0600 (CST) | |
From: Chris Lattner <sabre@nondot.org> | |
To: Vikram S. Adve <vadve@cs.uiuc.edu> | |
Subject: RE: Type notation debate... | |
> Arrays (without and with size): | |
> type ::= '[' type ']' | '[' INT ',' type ']'. | |
> | |
> The arrays with size lists the dimensions and the type in a single list. | |
> That is just too confusing: | |
> [10, 40, int] | |
> This seems to be a 3-D array where the third dimension is something strange. | |
> It is too confusing to have a list of 3 things, some of which are dimensions | |
> and one is a type. | |
The above grammar indicates that there is only one integer parameter, ie | |
the upper bound. The lower bound is always implied to be zero, for | |
several reasons: | |
* As a low level VM, we want to expose addressing computations | |
explicitly. Since the lower bound must always be known in a high level | |
language statically, the language front end can do the translation | |
automatically. | |
* This fits more closely with what Java needs, ie what we need in the | |
short term. Java arrays are always zero based. | |
If a two element list is too confusing, I would recommend an alternate | |
syntax of: | |
type ::= '[' type ']' | '[' INT 'x' type ']'. | |
For example: | |
[12 x int] | |
[12x int] | |
[ 12 x [ 4x int ]] | |
Which is syntactically nicer, and more explicit. | |
> Either of the following would be better: | |
> array [10, 40] of int | |
I considered this approach for arrays in general (ie array of int/ array | |
of 12 int), but found that it made declarations WAY too long. Remember | |
that because of the nature of llvm, you get a lot of types strewn all over | |
the program, and using the 'typedef' like facility is not a wonderful | |
option, because then types aren't explicit anymore. | |
I find this email interesting, because you contradict the previous email | |
you sent, where you recommend that we stick to C syntax.... | |
-Chris | |