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| 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
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