Re: Why ML/OCaml are good for writing compilers

Tony Bass <aeb@saltfarm.bt.co.uk>
30 Jul 1998 23:18:49 -0400

          From comp.compilers

Related articles
Why ML/OCaml are good for writing compilers dwight@pentasoft.com (1998-07-28)
Re: Why ML/OCaml are good for writing compilers aeb@saltfarm.bt.co.uk (Tony Bass) (1998-07-30)
Re: Why ML/OCaml are good for writing compilers amitp@Theory.Stanford.EDU (Amit Patel) (1998-08-13)
Re: Why ML/OCaml are good for writing compilers cfc@world.std.com (Chris F Clark) (1998-08-16)
Re: Why ML/OCaml are good for writing compilers bonnardv@pratique.fr (Valentin Bonnard) (1998-08-16)
| List of all articles for this month |

From: Tony Bass <aeb@saltfarm.bt.co.uk>
Newsgroups: comp.compilers
Date: 30 Jul 1998 23:18:49 -0400
Organization: DSP downstreaming
References: 98-07-220
Keywords: practice, functional

> From: dwight@pentasoft.com (Dwight VandenBerghe)
> [...] So although when I am writing about "ML"
> I am writing about Ocaml, what I say also applies, I think, to SML/NJ.


> So here is an unordered list of language features that seems to me
> to make writing compilers a pleasure rather than a horrendous chore.
> [...]


I heartily agree (though noting that my own experience is more with
compiler-like things than compilers themselves). And besides all
these splendid basic things there is the possibility of using
demand-driven evaluation for parsing, in caml-light with the stream
extension, and I imagine similar things are possible in Ocaml and
SML/NJ.


With caml-light streams one can write a set of mutually recursive
routines matching stream patterns against the input, often very close
to a BNF grammar notation apart from syntactic noise and semantic
restrictions,


      and galt = function
        [< gconcat e1;
              (parselist gconcat) e2
        >] -> makeseqlist (e1::e2)


      and gexpr = function
        [< galt e1;
              (parselist (function [< 'Hch `|`; galt e >] -> e)) e2;
              (parseoption (function [< 'Hch `#`; 'Hint n >] -> n)) _
        >] -> makealtlist e1 e2


with the right hand side after -> giving the semantic translation; and
the basic concepts of syntactic list and option of anything are
themselves defined in the same notation,


      let rec parselist f = function
            [< f x; s >] -> x :: (parselist f s)
        | [< >] -> [];;


      let parseoption f = function
            [< f x >] -> Some x
        | [< >] -> None;;


Another good tool in the tool-box.


--
# A E Bass Tel: (01473) 645305
# MLB 3/19, BT Laboratories e-mail: aeb@saltfarm.bt.co.uk
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