From c4ccd6ee72b2308244c7ef6c51e3742b819c819c Mon Sep 17 00:00:00 2001
From: Ozzie Gooen <ozzieagooen@gmail.com>
Date: Sat, 30 Apr 2022 13:17:22 -0400
Subject: [PATCH] Continuation in attempting to refactor SymbolicDist

---
 .../SymbolicDist/SymbolicDist.res             | 28 +++++++++-----
 .../src/rescript/Utility/SafeMath.res         | 38 +++++++++++++++++++
 2 files changed, 57 insertions(+), 9 deletions(-)
 create mode 100644 packages/squiggle-lang/src/rescript/Utility/SafeMath.res

diff --git a/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res b/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
index c44a972c..92a8277d 100644
--- a/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
+++ b/packages/squiggle-lang/src/rescript/Distributions/SymbolicDist/SymbolicDist.res
@@ -10,7 +10,9 @@ type rec error =
   | NotFinite(string, string, float)
   | DivideByZero(string)
   | NormalError(normalError)
+  | SafeMath(SafeMath.error)
   | MultipleErrors(array<error>)
+  | NinetiethPercentileShouldBeOrdered
 
 module Error = {
   let mapErrorArrayToError = (errors: array<error>): option<error> => {
@@ -51,8 +53,12 @@ module Normal = {
   let from90PercentCI = (low, high) => {
     let construct = () => {
       let mean = E.A.Floats.mean([low, high])
-      let stdev = (high -. low) /. (2. *. normal95confidencePoint)
-      make(~mean, ~stdev)
+      let stdev =
+        SafeMath.F.divide(
+          ~num=high -. low,
+          ~denominator=2. *. normal95confidencePoint,
+        )->E.R2.errMap(r => SafeMath(r))
+      stdev->E.R.bind(stdev => make(~mean, ~stdev))
     }
     [
       Error.checkIsFinite(low, "Normal", "low"),
@@ -75,7 +81,7 @@ module Normal = {
     dangerouslyMake(~mean, ~stdev)
   }
 
-  // TODO: is this useful here at all? would need the integral as well ...
+  // Note: This isn't being used right now
   let pointwiseProduct = (n1: t, n2: t) => {
     let mean =
       (n1.mean *. n2.stdev ** 2. +. n2.mean *. n1.stdev ** 2.) /. (n1.stdev ** 2. +. n2.stdev ** 2.)
@@ -104,11 +110,15 @@ module Normal = {
     | #Subtract => Some(make(~mean=n1.mean -. n2, ~stdev=n1.stdev))
     | #Multiply => Some(make(~mean=n1.mean *. n2, ~stdev=n1.stdev *. Js.Math.abs_float(n2)))
     | #Divide =>
-      [Error.divideByZero(n2, "Normal operateFloatSecond")]
-      ->ifNoErrorsThanDo(() => {
-        make(~mean=n1.mean /. n2, ~stdev=n1.stdev /. Js.Math.abs_float(n2))
-      })
-      ->Some
+      {
+        let mean = SafeMath.F.divide(~num=n1.mean, ~denominator=n2)->E.R2.errMap(r => SafeMath(r))
+        let stdev =
+          SafeMath.F.divide(
+            ~num=n1.stdev,
+            ~denominator=Js.Math.abs_float(n2),
+          )->E.R2.errMap(r => SafeMath(r))
+        E.R.merge(mean, stdev)->E.R.bind(((mean, stdev)) => make(~mean, ~stdev))
+      }->Some
     | _ => None
     }
 }
@@ -279,7 +289,7 @@ module From90thPercentile = {
     switch (low, high) {
     | (low, high) if low <= 0.0 && low < high => Normal.from90PercentCI(low, high)
     | (low, high) if low < high => Ok(Lognormal.from90PercentCI(low, high))
-    | (_, _) => Error("Low value must be less than high value.")
+    | (_, _) => Error(NinetiethPercentileShouldBeOrdered)
     }
 }
 
diff --git a/packages/squiggle-lang/src/rescript/Utility/SafeMath.res b/packages/squiggle-lang/src/rescript/Utility/SafeMath.res
new file mode 100644
index 00000000..e5517e7e
--- /dev/null
+++ b/packages/squiggle-lang/src/rescript/Utility/SafeMath.res
@@ -0,0 +1,38 @@
+@genType
+type rec error =
+  | DivideByZero
+  | IsNaN
+  | IsInfinite
+  | NotFinite(string, float)
+
+module Error = {
+  let checkIsFinite = (value, fnName) =>
+    E.Float.isFinite(value) ? None : Some(NotFinite(fnName, value))
+
+  let divideByZero = value => 0.0 == value ? None : Some(DivideByZero)
+}
+
+module Float = {
+  type t = float
+  let make = (v: t) =>
+    switch Error.checkIsFinite(v, "toSafe") {
+    | None => Ok(v)
+    | Some(e) => Error(e)
+    }
+}
+
+module F = {
+  type t = float
+  let divide = (~num: t, ~denominator: t) => {
+    if denominator == 0.0 {
+      Error(DivideByZero)
+    } else {
+      let result = num /. denominator
+      if E.Float.isFinite(result) {
+        Ok(result)
+      } else {
+        Error(NotFinite("divide", result))
+      }
+    }
+  }
+}