diff --git a/packages/squiggle-lang/__tests__/Distributions/Invariants/AlgebraicCombination_test.res b/packages/squiggle-lang/__tests__/Distributions/Invariants/AlgebraicCombination_test.res
index 718a4e14..a0f492a1 100644
--- a/packages/squiggle-lang/__tests__/Distributions/Invariants/AlgebraicCombination_test.res
+++ b/packages/squiggle-lang/__tests__/Distributions/Invariants/AlgebraicCombination_test.res
@@ -46,7 +46,7 @@ describe("(Algebraic) addition of distributions", () => {
       ->E.R2.fmap(DistributionTypes.Constructors.UsingDists.mean)
       ->E.R2.fmap(run)
       ->E.R2.fmap(toFloat)
-      ->E.R.toExn
+      ->E.R.toExn("Expected float", _)
       ->expect
       ->toBe(Some(2.5e1))
     })
@@ -60,7 +60,7 @@ describe("(Algebraic) addition of distributions", () => {
         ->E.R2.fmap(DistributionTypes.Constructors.UsingDists.mean)
         ->E.R2.fmap(run)
         ->E.R2.fmap(toFloat)
-        ->E.R.toExn
+        ->E.R.toExn("Expected float", _)
       switch received {
       | None => "algebraicAdd has"->expect->toBe("failed")
       // This is nondeterministic, we could be in a situation where ci fails but you click rerun and it passes, which is bad.
@@ -77,7 +77,7 @@ describe("(Algebraic) addition of distributions", () => {
         ->E.R2.fmap(DistributionTypes.Constructors.UsingDists.mean)
         ->E.R2.fmap(run)
         ->E.R2.fmap(toFloat)
-        ->E.R.toExn
+        ->E.R.toExn("Expected float", _)
       switch received {
       | None => "algebraicAdd has"->expect->toBe("failed")
       // This is nondeterministic, we could be in a situation where ci fails but you click rerun and it passes, which is bad.
@@ -158,7 +158,7 @@ describe("(Algebraic) addition of distributions", () => {
         ->E.R2.fmap(d => DistributionTypes.Constructors.UsingDists.pdf(d, 1e1))
         ->E.R2.fmap(run)
         ->E.R2.fmap(toFloat)
-        ->E.R.toExn
+        ->E.R.toExn("Expected float", _)
       switch received {
       | None => "algebraicAdd has"->expect->toBe("failed")
       // This is nondeterministic, we could be in a situation where ci fails but you click rerun and it passes, which is bad.
@@ -173,7 +173,7 @@ describe("(Algebraic) addition of distributions", () => {
         ->E.R2.fmap(d => DistributionTypes.Constructors.UsingDists.pdf(d, 1e1))
         ->E.R2.fmap(run)
         ->E.R2.fmap(toFloat)
-        ->E.R.toExn
+        ->E.R.toExn("Expected float", _)
       switch received {
       | None => "algebraicAdd has"->expect->toBe("failed")
       // This is nondeterministic, we could be in a situation where ci fails but you click rerun and it passes, which is bad.
@@ -249,7 +249,7 @@ describe("(Algebraic) addition of distributions", () => {
         ->E.R2.fmap(d => DistributionTypes.Constructors.UsingDists.cdf(d, 1e1))
         ->E.R2.fmap(run)
         ->E.R2.fmap(toFloat)
-        ->E.R.toExn
+        ->E.R.toExn("Expected float", _)
       switch received {
       | None => "algebraicAdd has"->expect->toBe("failed")
       // This is nondeterministic, we could be in a situation where ci fails but you click rerun and it passes, which is bad.
@@ -264,7 +264,7 @@ describe("(Algebraic) addition of distributions", () => {
         ->E.R2.fmap(d => DistributionTypes.Constructors.UsingDists.cdf(d, 1e1))
         ->E.R2.fmap(run)
         ->E.R2.fmap(toFloat)
-        ->E.R.toExn
+        ->E.R.toExn("Expected float", _)
       switch received {
       | None => "algebraicAdd has"->expect->toBe("failed")
       // This is nondeterministic, we could be in a situation where ci fails but you click rerun and it passes, which is bad.
@@ -341,7 +341,7 @@ describe("(Algebraic) addition of distributions", () => {
         ->E.R2.fmap(d => DistributionTypes.Constructors.UsingDists.inv(d, 2e-2))
         ->E.R2.fmap(run)
         ->E.R2.fmap(toFloat)
-        ->E.R.toExn
+        ->E.R.toExn("Expected float", _)
       switch received {
       | None => "algebraicAdd has"->expect->toBe("failed")
       // This is nondeterministic, we could be in a situation where ci fails but you click rerun and it passes, which is bad.
@@ -356,7 +356,7 @@ describe("(Algebraic) addition of distributions", () => {
         ->E.R2.fmap(d => DistributionTypes.Constructors.UsingDists.inv(d, 2e-2))
         ->E.R2.fmap(run)
         ->E.R2.fmap(toFloat)
-        ->E.R.toExn
+        ->E.R.toExn("Expected float", _)
       switch received {
       | None => "algebraicAdd has"->expect->toBe("failed")
       // This is nondeterministic, we could be in a situation where ci fails but you click rerun and it passes, which is bad.
diff --git a/packages/squiggle-lang/__tests__/Distributions/Invariants/Means_test.res b/packages/squiggle-lang/__tests__/Distributions/Invariants/Means_test.res
index 3806c7f9..fbc17114 100644
--- a/packages/squiggle-lang/__tests__/Distributions/Invariants/Means_test.res
+++ b/packages/squiggle-lang/__tests__/Distributions/Invariants/Means_test.res
@@ -50,7 +50,7 @@ module Internals = {
     let dist1 = dist1'->DistributionTypes.Symbolic
     let dist2 = dist2'->DistributionTypes.Symbolic
     let received =
-      distOp(dist1, dist2)->E.R2.fmap(mean)->E.R2.fmap(run)->E.R2.fmap(toFloat)->E.R.toExn
+      distOp(dist1, dist2)->E.R2.fmap(mean)->E.R2.fmap(run)->E.R2.fmap(toFloat)->E.R.toExn("Expected float", _)
     let expected = floatOp(runMean(dist1), runMean(dist2))
     switch received {
     | None => expectImpossiblePath(description)
@@ -82,12 +82,12 @@ describe("Means are invariant", () => {
     let testAdditionMean = testOperationMean(algebraicAdd, "algebraicAdd", \"+.", ~epsilon)
 
     testAll("with two of the same distribution", distributions, dist => {
-      E.R.liftM2(testAdditionMean, dist, dist)->E.R.toExn
+      E.R.liftM2(testAdditionMean, dist, dist)->E.R.toExn("Means were not invariant", _)
     })
 
     testAll("with two different distributions", pairsOfDifferentDistributions, dists => {
       let (dist1, dist2) = dists
-      E.R.liftM2(testAdditionMean, dist1, dist2)->E.R.toExn
+      E.R.liftM2(testAdditionMean, dist1, dist2)->E.R.toExn("Means were not invariant", _)
     })
 
     testAll(
@@ -95,7 +95,7 @@ describe("Means are invariant", () => {
       pairsOfDifferentDistributions,
       dists => {
         let (dist1, dist2) = dists
-        E.R.liftM2(testAdditionMean, dist2, dist1)->E.R.toExn
+        E.R.liftM2(testAdditionMean, dist2, dist1)->E.R.toExn("Means were not invariant", _)
       },
     )
   })
@@ -109,12 +109,12 @@ describe("Means are invariant", () => {
     )
 
     testAll("with two of the same distribution", distributions, dist => {
-      E.R.liftM2(testSubtractionMean, dist, dist)->E.R.toExn
+      E.R.liftM2(testSubtractionMean, dist, dist)->E.R.toExn("Means were not invariant", _)
     })
 
     testAll("with two different distributions", pairsOfDifferentDistributions, dists => {
       let (dist1, dist2) = dists
-      E.R.liftM2(testSubtractionMean, dist1, dist2)->E.R.toExn
+      E.R.liftM2(testSubtractionMean, dist1, dist2)->E.R.toExn("Means were not invariant", _)
     })
 
     testAll(
@@ -122,7 +122,7 @@ describe("Means are invariant", () => {
       pairsOfDifferentDistributions,
       dists => {
         let (dist1, dist2) = dists
-        E.R.liftM2(testSubtractionMean, dist2, dist1)->E.R.toExn
+        E.R.liftM2(testSubtractionMean, dist2, dist1)->E.R.toExn("Means were not invariant", _)
       },
     )
   })
@@ -136,12 +136,12 @@ describe("Means are invariant", () => {
     )
 
     testAll("with two of the same distribution", distributions, dist => {
-      E.R.liftM2(testMultiplicationMean, dist, dist)->E.R.toExn
+      E.R.liftM2(testMultiplicationMean, dist, dist)->E.R.toExn("Means were not invariant", _)
     })
 
     testAll("with two different distributions", pairsOfDifferentDistributions, dists => {
       let (dist1, dist2) = dists
-      E.R.liftM2(testMultiplicationMean, dist1, dist2)->E.R.toExn
+      E.R.liftM2(testMultiplicationMean, dist1, dist2)->E.R.toExn("Means were not invariant", _)
     })
 
     testAll(
@@ -149,7 +149,7 @@ describe("Means are invariant", () => {
       pairsOfDifferentDistributions,
       dists => {
         let (dist1, dist2) = dists
-        E.R.liftM2(testMultiplicationMean, dist2, dist1)->E.R.toExn
+        E.R.liftM2(testMultiplicationMean, dist2, dist1)->E.R.toExn("Means were not invariant", _)
       },
     )
   })
diff --git a/packages/squiggle-lang/src/rescript/Distributions/SampleSetDist/SampleSetDist.res b/packages/squiggle-lang/src/rescript/Distributions/SampleSetDist/SampleSetDist.res
index bb5f17d6..d62396f8 100644
--- a/packages/squiggle-lang/src/rescript/Distributions/SampleSetDist/SampleSetDist.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/SampleSetDist/SampleSetDist.res
@@ -96,6 +96,6 @@ let map2 = (
   // I could prove this to the type system (say, creating a {first: float, second: float, ..., fifth: float, rest: array<float>}
   // But doing so would take too much time, so I'll leave it as an assertion
   E.A.R.firstErrorOrOpen(samples)->E.R2.fmap(x =>
-    E.R.assertOk("Input of samples should be larger than 5", make(x))
+    E.R.toExn("Input of samples should be larger than 5", make(x))
   )
 }
diff --git a/packages/squiggle-lang/src/rescript/Utility/E.res b/packages/squiggle-lang/src/rescript/Utility/E.res
index 779ab03a..3b011877 100644
--- a/packages/squiggle-lang/src/rescript/Utility/E.res
+++ b/packages/squiggle-lang/src/rescript/Utility/E.res
@@ -160,12 +160,12 @@ module R = {
   let id = e => e |> result(U.id, U.id)
   let fmap = Rationale.Result.fmap
   let bind = Rationale.Result.bind
-  let toExn = Belt.Result.getExn
-  let assertOk = (message: string, x: result<'a, 'b>): 'a =>
+  let toExn = (msg: string, x: result<'a, 'b>): 'a =>
     switch x {
     | Ok(r) => r
-    | Error(_) => raise(Assertion(message))
+    | Error(_) => raise(Assertion(msg))
     }
+
   let default = (default, res: Belt.Result.t<'a, 'b>) =>
     switch res {
     | Ok(r) => r