Introducing $*RAT-UPGRADE-CLASS

src/core.c/Exception.pm6

@@ -91,6 +91,10 @@ my class Exception {
 
     method is-compile-time(--> False) { }
     method message() { ... }
+
+    method UPGRADE-RAT(Int $nu, Int $de) {
+        die "Upgrading of Rat $nu / $de not allowed"
+    }
 }
 
 my class X::SecurityPolicy is Exception {}
@@ -398,6 +402,11 @@ my class CX::Take does X::Control {
 }
 my class CX::Warn does X::Control {
     has $.message;
+
+    method UPGRADE-RAT(Int $nu, Int $de) is raw {
+        warn "Downgrading Rat $nu / $de to Num";
+        nqp::p6box_n(nqp::div_In($nu,$de))
+    }
 }
 my class CX::Succeed does X::Control {
     method message() { "<succeed control exception>" }

src/core.c/Failure.pm6

@@ -130,6 +130,9 @@ my class Failure is Nil {
     method STORE(Failure:D: *@) {
         self!throw()
     }
+    method UPGRADE-RAT(Int $nu, Int $de) {
+        Failure.new("Upgrading of Rat $nu / $de not allowed")
+    }
 }
 
 proto sub fail(|) {*};

src/core.c/Num.pm6

@@ -283,6 +283,10 @@ my class Num does Real { # declared in BOOTSTRAP
             ?? $i
             !! self
     }
+
+    method UPGRADE-RAT(\nu, \de) is raw {
+        nqp::p6box_n(nqp::div_In(nu,de))  # downgrade to float
+    }
 }
 
 my constant tau = 6.28318_53071_79586_476e0;

src/core.c/Rat.pm6

@@ -40,6 +40,13 @@ my class FatRat is Cool does Rational[Int, Int] {
     multi method raku(FatRat:D: --> Str:D) {
         "FatRat.new($!numerator, $!denominator)";
     }
+
+    method UPGRADE-RAT(\nu, \de) is raw {
+        nqp::p6bindattrinvres(
+          nqp::p6bindattrinvres(nqp::create(FatRat),FatRat,'$!numerator',nu),
+          FatRat,'$!denominator',de
+        )
+    }
 }
 
 # NORMALIZE two integer values and create a Rat/FatRat/float from them.
@@ -72,6 +79,9 @@ sub DIVIDE_NUMBERS(
     )
 }
 
+# Initialize the $*RAT-UPGRADE-POLICY dynamic var so that it can be used
+PROCESS::<$RAT-UPGRADE-POLICY> = Num;
+
 # ALL RATIONALS MUST BE NORMALIZED, however in some operations we cannot
 # ever get a non-normalized Rational, if we start with a normalized Rational.
 # For such cases, we can use this routine, to bypass normalization step,
@@ -83,6 +93,7 @@ multi sub CREATE_RATIONAL_FROM_INTS(Int:D $nu, Int:D $de, Any, Any) is raw {
            nqp::p6bindattrinvres(nqp::create(Rat),Rat,'$!numerator',$nu),
            Rat,'$!denominator',$de
          )
+      !! $*RAT-UPGRADE-POLICY.UPGRADE-RAT(nu, de)
       !! nqp::p6box_n(nqp::div_In($nu,$de))  # downgrade to float
 }
 

t/08-performance/05-processkeys.t

@@ -13,6 +13,7 @@ my $allowed = (
   Q{$PID},
   Q{$RAKU},
   Q{$RAKUDO_MODULE_DEBUG},
+  Q{$RAT-UPGRADE-POLICY},
   Q{$REPO},
   Q{$SCHEDULER},
   Q{$SPEC},