tweak: Add error checking to dmr calculation

packages/squiggle-lang/src/rescript/FunctionRegistry/Library/FR_Danger.res

@@ -272,6 +272,29 @@ module DiminishingReturns = {
       1. O(n): Iterate through value on next n dollars. At each step, only compute the new marginal return of the function which is spent
       2. O(n*m): Iterate through all possible spending combinations. The advantage of this option is that it wouldn't assume that the returns of marginal spending are diminishing.
  */
+      switch (
+        E.A.length(lambdas) > 1,
+        funds > 0.0,
+        approximateIncrement > 0.0,
+        funds > approximateIncrement,
+      ) {
+      | (false, _, _, _) =>
+        Error(
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, number of functions should be greater than 1.",
+        )
+      | (_, false, _, _) =>
+        Error(
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, funds should be greater than 0.",
+        )
+      | (_, _, false, _) =>
+        Error(
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be greater than 0.",
+        )
+      | (_, _, _, false) =>
+        Error(
+          "Error in Danger.optimalAllocationGivenDiminishingMarginalReturnsForManyFunctions, approximateIncrement should be smaller than funds amount.",
+        )
+      | (true, true, true, true) => {
           let applyFunctionAtPoint = (lambda, point: float) => {
             // Defined here so that it has access to environment, reducer
             let pointAsInternalExpression = FunctionRegistry_Helpers.Wrappers.evNumber(point)
@@ -355,9 +378,8 @@ module DiminishingReturns = {
           }
 
           optimalAllocationResult
-      // let result = [0.0, 0.0]->FunctionRegistry_Helpers.Wrappers.evArrayOfEvNumber->Ok
+        }
-      // result
+      }
-      // ^ helper with the same type as what the result should be. Useful for debugging.
     }
   }
   module Lib = {