Added delta function to produce delta distributions

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

@@ -219,6 +219,12 @@ module Uniform = {
 module Float = {
   type t = float
   let make = t => #Float(t)
+  let makeSafe = t =>
+    if E.Float.isFinite(t) {
+      Ok(#Float(t))
+    } else {
+      Error("Float must be finite")
+    }
   let pdf = (x, t: t) => x == t ? 1.0 : 0.0
   let cdf = (x, t: t) => x >= t ? 1.0 : 0.0
   let inv = (p, t: t) => p < t ? 0.0 : 1.0

packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_GenericDistribution.res

@@ -179,10 +179,12 @@ let dispatchToGenericOutput = (call: ExpressionValue.functionCall): option<
 > => {
   let (fnName, args) = call
   switch (fnName, args) {
-  | ("exponential" as fnName, [EvNumber(f1)]) =>
+  | ("exponential" as fnName, [EvNumber(f)]) =>
     SymbolicConstructors.oneFloat(fnName)
-    ->E.R.bind(r => r(f1))
+    ->E.R.bind(r => r(f))
     ->SymbolicConstructors.symbolicResultToOutput
+  | ("delta", [EvNumber(f)]) =>
+    SymbolicDist.Float.makeSafe(f)->SymbolicConstructors.symbolicResultToOutput
   | (
       ("normal" | "uniform" | "beta" | "lognormal" | "cauchy" | "to") as fnName,
       [EvNumber(f1), EvNumber(f2)],

packages/squiggle-lang/src/rescript/Utility/E.res

@@ -198,6 +198,7 @@ module Float = {
   let with3DigitsPrecision = Js.Float.toPrecisionWithPrecision(_, ~digits=3)
   let toFixed = Js.Float.toFixed
   let toString = Js.Float.toString
+  let isFinite = Js.Float.isFinite
 }
 
 module I = {