[mercury-users] currying does not work with higher order predicates ?

[Tyson Dowd]

Mercury doesn't really allow implicit currying everywhere, you
can't just add arguments to an existing closure, but instead you
have to write an explicit lambda expression:

e.g. (func(X) = ....) or (pred(X::in) :- ....)

So try:

io__write_list(XForms, ",\n", 
	(pred(A::in, di, uo) ---> WriteXForm("di", "uo", A) )),
io__write_list(XForms, ",\n", 
	(pred(A::in, di, uo) ---> WriteXForm("in", "out", A) )),


On 24-Jul-2001, Holger Krug <hkrug at rationalizer.com> wrote:
> I currently make some changes to moose to "allow the parsing state to
> be unique (so that it can contain the io:state, just for example)."
> 
> To this purpose it tried to modify existing moose code to something like:
> 
> 	{ WriteXForm = (pred(InMode::in, OutMode::in, XForm::in, di, uo) 
> 		is det -->
> 		{ XForm = xform(NT, MethodName) },
> 		{ lookup(Decls, NT, RuleDecl) },
> 		{ RuleDecl = rule(_NT, Types, VarSet, _Context) },
> 		io__write_strings(["\tpred ", MethodName, "("]),
> 		io__write_list(Types, ", ", term_io__write_term(VarSet)),
> 		( { Types \= [] } -> io__write_string(", ") ; [] ),
> 		io__write_string("T, T),\n"),
> 
> 		io__write_strings(["\tmode ", MethodName, "("]),
> 		io__write_list(Types, ", ", WriteIn),
> 		( { Types \= [] } -> io__write_string(", ") ; [] ),
> 		io__write_string(InMode),
> 		io__write_string(", "),
> 		io__write_string(OutMode),
> 		io__write_string(") is det")
> 		)
> 	},
> 	( { UniqueModes = yes } ->
> #279	    io__write_list(XForms, ",\n", WriteXForm("di", "uo"))
> 	;
> #281	    io__write_list(XForms, ",\n", WriteXForm("in", "out"))
> 	),
> 
> #xxx are the line numbers.
> 
> I get the following error messages:
> 
> moose.m:279: In clause for predicate `moose:write_action_type_class/6':
> moose.m:279:   in argument 3 of call to predicate `io:write_list/5':
> moose.m:279:   in unification of argument
> moose.m:279:   and term `''(WriteXForm, V_46, V_47)':
> moose.m:279:   type error in argument(s) of functor `/3'.
> moose.m:279:   Argument 1 (WriteXForm) has type `pred(string, string, (grammar:xform), (io:state), (io:state))',
> moose.m:279:   expected type was `(func(V_30, V_29) = V_31)'.
> moose.m:281: In clause for predicate `moose:write_action_type_class/6':
> moose.m:281:   in argument 3 of call to predicate `io:write_list/5':
> moose.m:281:   in unification of argument
> moose.m:281:   and term `''(WriteXForm, V_50, V_51)':
> moose.m:281:   type error in argument(s) of functor `/3'.
> moose.m:281:   Argument 1 (WriteXForm) has type `pred(string, string, (grammar:xform), (io:state), (io:state))',
> moose.m:281:   expected type was `(func(V_31, V_30) = V_32)'.
> 
> It seems as if currying is not allowed for higher order predicates.
> Is this assumption correct or did I make some other kind of error ?
> 
>  -- 
> Holger Krug
> hkrug at rationalizer.com
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