[OpenBIOS] Fwd: [PATCH] Adds local variable support to OpenBIOS.

[Programmingkid]

On Aug 28, 2012, at 2:50 AM, openbios-request at openbios.org wrote:

> Message: 1
> Date: Mon, 27 Aug 2012 21:18:08 -0400
> From: Tarl Neustaedter <tarl-b2 at tarl.net>
> To: The OpenBIOS Mailinglist <openbios at openbios.org>
> Subject: Re: [OpenBIOS] [PATCH] Adds local variable support to
> 	OpenBIOS.
> Message-ID: <503C1C50.408 at tarl.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> [...]
> 
> 
>>> 
>>> And don't use CamelCase.
>> 
>> Is this some official naming convention, or your own taste?
> 
> In general (at least in the 1275 world), Forth is case-insensitive. The 
> rare cases where it is made case sensitive (there are a couple in Sun's 
> Openboot - see dropins.src) make use of mixed case very painful. The 
> general standard is that methods and variables are lower case, defined 
> constants and structure offsets are upper case. In some code, even they 
> are lower case.
> 
> Mixed-case is generally confined to comments.

Are you saying my-variable is better than myVariable?

> 
>>> Factor this?  You shouldn't ever use a variable that is used as a temp
>>> inside a word.
>> 
>> I'm not sure why you suggest this. It is just such a pain having to 
>> deal with the stack.
> 
> Because using a global variable gets you in trouble in recursion or when 
> the same code is called at alarm level. As for stack being a pain, yes, 
> that's forth. Stack manipulation as a way of life. Personally, I prefer 
> "2over nip" rather than "2 pick" :-)

How do global variables get you in trouble in recursion? Do you have an example?

I am not familiar with this alarm level. Could you explain what it is? 

> 
>>>> +48 CONSTANT localTableSize
>>>> +
>>>> +\ Declare the local variable table
>>>> +localTableSize ARRAY localVariableTable
>>> 
>>> You have 48 but can only access 12?
>> 
>> That is four fields per local variable: 48 / 4 = 12.
> 
> At a minimum, any derived constants should be derived explicitly. Like:
> 
> 12 constant #local-variables     \ Feels right. If you need more, add 
> more code after Locals11.
> 4 constant /local-variable       \ Datastructures require four cells
> #local-variables /local-variable * constant locals-table-size \ Size in 
> cells, not bytes.
> 
> Ah. That points out another convention. When mashing together multiple 
> words for a method or variable name, we tend to use dashes as separators 
> (and please, don't use underscores. There is someone I know who *mixes* 
> underscores and dashes in variable names!). Another is that sizes of 
> things are usually /object (such as /n, /l, ...) and counts of objects 
> are usually #object.

Ok. Sounds reasonable.

> 
>> 
>>> 
>>>> +: getLocalRecordCount
>>>> +arrayCount 4 /
>>>> +;
>>> 
>>> Oh.  Use a struct?
>> 
>> The little documentation on struct I found did not indicate it was a 
>> better replacement for Array.
> 
> Struct will allow you define what the four separate words used in each 
> local variable entry are used for. If you use structs, I'd expect to see 
> something like:
> 
> struct
>    /n field >LOCAL-INIT
>    /n field >LOCAL-ORDER
>    /n field >LOCAL-LEN
>    /n field >LOCAL-ADDR
> constant /local-variable
> 12 constant #local-variables
> /local-variable #local-variables constant locals-table-size
> 
> Note that the above provides the table size in bytes, rather than cells.
> 
> To use the above (assuming you are still using alloc-mem), you'd see 
> something like:
> 
>     locals-table-size alloc-mem     ( table )
>     #local-variables 0 do           ( table )
>       i /local-variable *           ( table entry )
>       0 over >LOCAL-INIT !          ( table entry )
>       0 over >LOCAL-ORDER !         ( table entry )
>       0 over >LOCAL-LEN !           ( table entry )
>       0 swap >LOCAL-ADDR !          ( table )
>    loop                             ( table )

That looks very unfriendly. There is no way I am using structs. 


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