Fixed implementation

Value: [0.4 to 2]

packages/squiggle-lang/src/rescript/Distributions/GenericDist/GenericDist.res

@@ -244,9 +244,13 @@ module AlgebraicCombination = {
     ~t2: t,
   ): result<t, error> => {
     let algebraicResult = run'(t1, ~toPointSetFn, ~toSampleSetFn, ~arithmeticOperation, ~t2)
-    switch mode {
-    | Some(_) => algebraicResult
-    | None => Error(RequestedModeInvalidError)
+    switch (mode, algebraicResult) {
+    | (None, _)
+    | (Some(AsSymbolic), Ok(Symbolic(_)))
+    | (Some(AsMontecarlo), Ok(DistributionTypes.SampleSet(_)))
+    | (Some(AsConvolution), Ok(DistributionTypes.PointSet(_)))
+    | (Some(_), Error(_)) => algebraicResult
+    | (Some(_), Ok(_)) => Error(RequestedModeInvalidError)
     }
   }
 }