🚀 go-pugleaf

On Friday, September 21, 2012 12:10:26 AM UTC+6, jdn wrote:
> I'm interested in using camlp4 for a DSL.  To get up to speed I was hoping to use camlp4 in the toplevel to expand quotations to help with the learning curve.  I can't seem to get this to work so I must be missing something, apologies if this is a very simple question.  Here is a snippit of what I'm doing and the error:
>
>
>
> utop $ #camlp4o;;
>
> utop $ open Camlp4.PreCast;;
>
> utop $ let q = <:str_item< let f x = x >>;;
>
> Error: While finding quotation "str_item" in a position of "expr": There is no quotation expander available.                                                               Camlp4: Uncaught exception: Not_found
>
>
>
> I've tried many different things and done a google search but I can't figure out the problem.  Any hints are greatly appreciated.


Greetings.

To be able to refer to the OCaml's str_item quotation you need to load the
corresponding findlib package (camlp4.quotations.o). An example of how to do it
in the vanilla toplevel:

    # #use "topfind";;
    - : unit = ()
    Findlib has been successfully loaded. Additional directives:
      #require "package";;      to load a package
      #list;;                   to list the available packages
      #camlp4o;;                to load camlp4 (standard syntax)
      #camlp4r;;                to load camlp4 (revised syntax)
      #predicates "p,q,...";;   to set these predicates
      Topfind.reset();;         to force that packages will be reloaded
      #thread;;                 to enable threads

    - : unit = ()
    # #camlp4o;;
    /usr/lib/ocaml/dynlink.cma: loaded
    /usr/lib/ocaml/camlp4: added to search path
    /usr/lib/ocaml/camlp4/camlp4o.cma: loaded
    	Camlp4 Parsing version 3.12.1

    # #require "camlp4.quotations.o";;
    /usr/lib/ocaml/camlp4/Camlp4Parsers/Camlp4QuotationCommon.cmo: loaded
    /usr/lib/ocaml/camlp4/Camlp4Parsers/Camlp4OCamlOriginalQuotationExpander.cmo: loaded

    # open Camlp4.PreCast;;
    # let _loc = Loc.ghost;;
    val _loc : Camlp4.PreCast.Loc.t = <abstr>

    # <:str_item< 42 >>;;
    - : Camlp4.PreCast.Ast.str_item =
    Camlp4.PreCast.Ast.StSem (<abstr>,
     Camlp4.PreCast.Ast.StExp (<abstr>, Camlp4.PreCast.Ast.ExInt (<abstr>, "42")),
     Camlp4.PreCast.Ast.StNil <abstr>)


Notice how we first bind a dummy location to _loc, because the expanded
quotation expects _loc to be available in the current lexical context.

Have fun hacking your DSL with Camlp4, and be prepared to face a lot of bizarre
black magic, since the official Camlp4 documentation leaves much to be desired.

Just read the source, Luke, and get enlightenment (or maybe brain damage) :-)