What is Expressiveness in a Computer Language

[Matthias Blume]

Darren New <dnew at san.rr.com> writes:

> Matthias Blume wrote:
>> Very good statically typed versions of printf exist.  See, e.g.,
>> Danvy's unparsing combinators.
>
> That seems to ignore the fact that the pattern is a string, which
> means that printf's first argument in Danvy's mechanism has to be a
> literal.

In Danvy's solution, the format argument is not a string.

> You can't read the printf format from a configuration file
> (for example) to support separate languages.

You don't need to do that if you want to support separate languages.
Moreover, reading the format string from external input is a good way
of opening your program to security attacks, since ill-formed data on
external media are then able to crash you program.

> It doesn't look like the
> version of printf that can print its arguments in an order different
> from the order provided in the argument list is supported either;
> something like "%3$d" or some such.

I am not familiar with the version of printf you are refering to, but
I am sure one could adapt Danvy's solution to support such a thing.

> Second, what's the type of the argument that printf, sprintf, fprintf,
> kprintf, etc all pass to the subroutine that actually does the
> formatting? (Called vprintf, I think?)

Obviously, a Danvy-style solution (see, e.g., the one in SML/NJ's
library) is not necessarily structured that way.  I don't see the
problem with typing, though.

Matthias