sml - Functors with multiple inputs in Standard ML -

high level question: how use functors multiple arguments in sml?

i've looked @ this, this, this , this(pdf). of them seem conflict in terms of structure or functor definition syntax, , none of them show other unary functor.

specifics: i'm trying write web server in standard ml (you can see effort here), , have decided partition buffer, parser , tcpserver chunks. buffer , parser both straightforward structures. idea tcpserver handles listening/accepting logic, allows user specify appropriate buffering/parsing strategy passing other 2 in. i've got like

signature tcpserver = sig     type sockaction     type request     val serve : int -> (request -> (inetsock.inet,socket.active socket.stream) socket.sock -> sockaction) -> 'u end  functor server (buf : buffer) (par : parser) : tcpserver = struct   type request = par.request   datatype sockaction = close | leave_open   local   ...    [eliding more definitions, including calls par.* , buf.* functions]   ...   fun serve port serverfn =       let val s = inetsock.tcp.socket()       in          socket.ctl.setreuseaddr (s, true);         socket.bind(s, inetsock.any port);         socket.listen(s, 5);         print "entering accept loop...\n";         acceptloop s [] serverfn       end   end end 

the above seems accepted smlnj...

- use "server.sml" ; [opening server.sml] type response =   {body:string, headers:(string * string) list, httpversion:string,    responsetype:string} val fst = fn : 'a * 'b -> 'a val snd = fn : 'a * 'b -> 'b val a_ = fn : 'a * 'b * 'c -> 'a val b_ = fn : 'a * 'b * 'c -> 'b val c_ = fn : 'a * 'b * 'c -> 'c val curry = fn : ('a * 'b -> 'c) -> 'a -> 'b -> 'c signature tcpserver =   sig     type sockaction     type request     val serve : int                 -> (request                     -> (inetsock.inet,socket.active socket.stream) socket.sock                        -> sockaction)                    -> 'a   end functor httpserver(buf: sig                           type buffer                           val readinto : buffer                                          -> ('a,socket.active socket.stream)                                                socket.sock                                             -> bufferstatus                           val new : int -> buffer                           val toslice : buffer -> word8arrayslice.slice                           val printbuffer : buffer -> unit                         end) :                   sig functor <functor> : <fctsig> end val = () : unit 

... rejected mlton.

~/projects/serve-sml $ mlton server.mlb error: server.sml 23.1. # (line "functor server...")   syntax error: replacing  functor  fun. error: server.sml 24.1.   syntax error: replacing  struct  asterisk. error: server.sml 87.1.   syntax error found @ end. error: server.sml 88.0.   parse error. ... 

additionally, i'm not entirely sure how use definition once it's evaluated. in smlnj, obvious fails:

- httpserver(defaultbuffer, defaultparser) ; stdin:1.2-1.12 error: unbound variable or constructor: httpserver stdin:2.7-3.1 error: unbound variable or constructor: defaultparser stdin:1.13-2.5 error: unbound variable or constructor: defaultbuffer -  

can tell me i'm doing wrong? or point me piece of documentation?

your server functor multiple arguments via currying. not work in plain sml, because not have higher-order functors (which sml/nj supports non-standard extension). need use uncurried form, introducing auxiliary structure, use tuple or record in core language:

functor server(x : sig structure buffer : buffer; structure parser : parser end) =   ...x.buffer...x.parser...  structure myserver =   server(struct structure buffer = mybuffer; structure parser = myparser end) 

obviously, pretty clumsy , verbose, @ least sml has syntactic sugar above, allowing keep auxiliary structure implicit:

functor server(structure buffer : buffer; structure parser : parser) =   ...buffer...parser...  structure myserver =   server(structure buffer = mybuffer; structure parser = myparser) 

but short gets in current sml.