1 Date: Thu, 8 Feb 2001 14:31:05 -0600 (CST) 2 From: Chris Lattner <sabre (a] nondot.org> 3 To: Vikram S. Adve <vadve (a] cs.uiuc.edu> 4 Subject: RE: Type notation debate... 5 6 > Arrays (without and with size): 7 > type ::= '[' type ']' | '[' INT ',' type ']'. 8 > 9 > The arrays with size lists the dimensions and the type in a single list. 10 > That is just too confusing: 11 12 > [10, 40, int] 13 > This seems to be a 3-D array where the third dimension is something strange. 14 > It is too confusing to have a list of 3 things, some of which are dimensions 15 > and one is a type. 16 17 The above grammar indicates that there is only one integer parameter, ie 18 the upper bound. The lower bound is always implied to be zero, for 19 several reasons: 20 21 * As a low level VM, we want to expose addressing computations 22 explicitly. Since the lower bound must always be known in a high level 23 language statically, the language front end can do the translation 24 automatically. 25 * This fits more closely with what Java needs, ie what we need in the 26 short term. Java arrays are always zero based. 27 28 If a two element list is too confusing, I would recommend an alternate 29 syntax of: 30 31 type ::= '[' type ']' | '[' INT 'x' type ']'. 32 33 For example: 34 [12 x int] 35 [12x int] 36 [ 12 x [ 4x int ]] 37 38 Which is syntactically nicer, and more explicit. 39 40 > Either of the following would be better: 41 > array [10, 40] of int 42 43 I considered this approach for arrays in general (ie array of int/ array 44 of 12 int), but found that it made declarations WAY too long. Remember 45 that because of the nature of llvm, you get a lot of types strewn all over 46 the program, and using the 'typedef' like facility is not a wonderful 47 option, because then types aren't explicit anymore. 48 49 I find this email interesting, because you contradict the previous email 50 you sent, where you recommend that we stick to C syntax.... 51 52 -Chris 53 54
