From 7a419742ad5f91afd07ff6a7deb828ad8c50632a Mon Sep 17 00:00:00 2001
From: Quinn Dougherty <quinnd@riseup.net>
Date: Mon, 4 Jul 2022 09:57:00 -0400
Subject: [PATCH] moved error message sooner for invalid mean and stdev

---
 .../Distributions/SymbolicDist/SymbolicDist.res      | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res b/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
index 0b192b5f..e7471ffa 100644
--- a/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
@@ -129,14 +129,18 @@ module Beta = {
     // https://en.wikipedia.org/wiki/Beta_distribution#Mean_and_sample_size
     let alpha = mean *. sampleSize
     let beta = (1.0 -. mean) *. sampleSize
-    alpha->make(beta)
+    make(alpha, beta)
   }
 
   let fromMeanAndStdev = (mean, stdev) => {
     // https://en.wikipedia.org/wiki/Beta_distribution#Mean_and_variance
-    let var = stdev *. stdev
-    let sampleSize = mean *. (1.0 -. mean) /. var -. 1.0
-    mean->fromMeanAndSampleSize(sampleSize)
+    if !(0.0 < stdev && stdev <= 0.5) || !(0.0 <= mean && mean <= 1.0) {
+      "Beta mean must be in [0,1] and stdev must be in (1,0.5]"->Error
+    } else {
+      let var = stdev *. stdev
+      let sampleSize = mean *. (1.0 -. mean) /. var -. 1.0
+      fromMeanAndSampleSize(mean, sampleSize)
+    }
   }
 }