Complexity Shock Horror II: the Sequel (was Re: MD5 in erlang

Raimo Niskanen <>
Mon Mar 31 14:31:45 CEST 2003


Some comments and some problems. Since Erlang supports the Base#Integer 
syntax i think that Base in:
	integer_to_list(Integer, Base)
should be 2..16, not atoms.

The same for:
	list_to_integer(List, Base)

But what should happen if you call list_to_integer("16#1f", 8), and how 
should you specify any base. I guess the answers are: badarg on the 
first and list_to_integer("16#1f", undefined) on the second question.

And to add the prefix in the Right(tm) way is a bit awkward:
	List = case integer_to_list(Integer, 16) of
		    [$-|L] -> "-16#"++L;
		    L -> "16#"++L
		end

/ Raimo



Tony Rogvall wrote:
> Raimo Niskanen wrote:
> 
>>
>> I am about to add your requested functionality to io_lib:format, so I 
>> thought about adding these BIFs too, but it turned out that it was 
>> hard to decide what they should do, exactly: Erlang-style prefix or 
>> not, lowercase or UPPERCASE or selectable and how to select, how to 
>> select any-base for list_to_integer/2, etc.
>>
>> It started to seem that an option list was needed with quite some 
>> options, and then they suddenly did seem too complicated to be BIFs.
>>
> Here is one suggestion for R9C
> 
> integer_to_list(Integer, Base)
> 
> where integer(Integer) and Base = bin | oct | hex or dec
> 
> - The prefix is not needed sice it is a constant op to cons "16#" or 
> whatever as a prefix.
> 
> - The case is not very important for hex numbers since most "readers" 
> can read both upper an lower case, correct me I you ever seen any 
> software (not your own:-) that care about case in hex numbers! . I vote 
> for uppercase, since that what is what I have seen most. If it should be 
> a problem then we can add 'heX' as uppercase option.
> 
> I wonder how many times I have written integer_to_hex? I am sure it must 
> be 100 times...
> 
> When we are at it, why not do the same thing for list_to_integer?
> I suggest:
>      list_to_integer(List, Base)  (base = bin | oct | hex | dec )
> 
> possibly allowing base spec in the list_to_integer/1 i.e 
> list_to_integer("16#1234")
> 
> 
> Raimo you can give me a call, I will be glad to help you :-)
> 
>> So I hope it will do to use something like 
>> lists:flatten(io_lib:format("~16b", [Integer])).
>>
>> If it is necessary for performance reasons, we might add these BIFs 
>> later.
>>
> 
> Why wait ? I do not think we can talk us out of this one :-)
> 
> /Tony




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