[Haskell-cafe] Re: Functional _meta_programming for processing of large raster images

oleg at pobox.com oleg at pobox.com
Wed Jun 21 18:20:29 EDT 2006

I'm afraid the _meta_ programming aspect of the image processing
project may be overlooked. 

Joel Reymont wrote:
> I think the issue wasn't using functional programming for large image  
> processing, it was using Haskell. OCaml is notoriously fast and  
> strict. Haskell/GHC is... lazy.

Well, in the raster image processing project, a dialect of OCaml was
used to _generate_ code. If the author used offshoring (which I think
they did later), the generated code was in C. That C code can be used
stand-alone or be linked with some other C (Java, etc) code. Our FFT
paper did exactly that: our MetaOCaml program produced C code, which
we plugged as it was in the FFTW testing framework (written in pure C)
for benchmarking. By 'plugged' above I meant moving the C code file
from one directory to another. We used both GCC and Intel C compilers
for benchmarking.  Offshoring can also produce Fortran code. It's
quite feasible to generate Verilog so we can program an FPGA and get
image processing even faster.

The generator doesn't have to be a speed demon; it is not that
relevant if the generator is lazy or strict. What really matters if
the generator can be easily judged correct. It immensely matters that
the generated code has correctness properties; at least, it should be
well-formed and well-typed (and preferably, has some other properties,
like space bounds). It is disheartening to see errors when compiling
the generated code (as happens with some other generators), because it
is very difficult to trace these errors back to the generator.

Here's the reference to another, quite large and very real project


which generates the fastest ever FFT, DCT, etc. codes for variety of
architectures. The source language is a DSL for linear algebra. The
point is that highest-performance computing nowadays is all about code
generation/meta-programming. And in this area, functional programming
and Haskell have definite advantage.

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