compiler confusion, overloading and "subtype mark required in this context"

[Mehdi Saada <00120260a@gmail.com>]

In an exo to build a rational integers package, I'm having the surprise to get a heapload of "context requires function call, found procedure name". While there is no procedure of these names.

   function "+" (R1: T_rational; R2: T_rational) return T_rational is
     (if (denom(R1) = denom(R2)) then (ENUM(R1) + ENUM(r2))/ denom(R1)
      else (DENOM(R2)*ENUM(R1) + denom(r1)*ENUM(r2))/DENOM(R1)*denom(R2));

   function denom (fraction: T_rational) return Positive is (fraction.denom);
   function enum (fraction: T_rational) return Natural is (fraction.ENUM);

with usually a "no candidate interpretations match the actuals:" for the same stuff. There are several overloaded operators, but each time with different profiles so I'm very surprised it could cause trouble.

Another kind of oddity: several
 function "+" (R1: T_rational; R2: T_rational) return T_rational is
     (if (denom(R1) = denom(R2)) then (ENUM(R1) + ENUM(r2))/ denom(R1)
      else (DENOM(R2)*ENUM(R1) + denom(r1)*ENUM(r2))/DENOM(R1)*denom(R2));
cause "ambiguous expression (cannot resolve "+")" with "possible interpretation". -- here it picks
function "+" (R1: T_rational; R2: T_rational) return T_rational;
as an interpretation, which is bullocks since obviously I'm calling on Integer operations, between enum() and denom(), integer and natural, then calling on the constructor "/" who is the only "/" with the specific profile
   function "/" (N: Integer; D: Integer) return T_rational;

additional questions. I already looked up the rm. is there an attribute to 'min/'max integer without the sign (I "abs"ed them) ?

Last one:

The commented lines:
 function Get_Line return T_rational is
      use ada.Integer_Text_IO;
   begin
      loop
         declare
            S: string := Get_Line;
            Enume: integer;
            Denomi: Positive; ---- ##########
            Ind : Natural range 0..1 := 0;
            sign : T_SIGN := Positive;
            Last: Positive;
         begin
            if S(1) = '-' then SIGN := negative; ind := 0; end if;
            Get(S(s'First+ind..s'Last), Enume, Last);
            if last = S'Last then return (IF SIGN = NEGATIVE => -Enume/1 else ENUMe/1); ----------######

Both last ones are "subtype mark required in this context" while he's refering to:    type T_SIGN is (positive,negative);
But how can there be confusion ?

Thanks. this exo is suprisingly taxing... the numbers of details that go wrong !