diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
index 582df17d..eed48ffc 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
@@ -11,7 +11,6 @@ type rec frType =
   | FRTypeLambda
   | FRTypeRecord(frTypeRecord)
   | FRTypeArray(frType)
-  | FRTypeOption(frType)
   | FRTypeString
   | FRTypeVariant(array<string>)
 and frTypeRecord = array<frTypeRecordParam>
@@ -24,7 +23,6 @@ and frTypeRecordParam = (string, frType)
 type rec frValue =
   | FRValueNumber(float)
   | FRValueDist(DistributionTypes.genericDist)
-  | FRValueOption(option<frValue>)
   | FRValueArray(array<frValue>)
   | FRValueDistOrNumber(frValueDistOrNumber)
   | FRValueRecord(frValueRecord)
@@ -60,7 +58,6 @@ module FRType = {
         `record({${r->E.A2.fmap(input)->E.A2.joinWith(", ")}})`
       }
     | FRTypeArray(r) => `record(${toString(r)})`
-    | FRTypeOption(v) => `option(${toString(v)})`
     | FRTypeLambda => `lambda`
     | FRTypeString => `string`
     | FRTypeVariant(_) => "variant"
@@ -75,7 +72,6 @@ module FRType = {
     | (FRTypeDistOrNumber, EvDistribution(f)) => Some(FRValueDistOrNumber(FRValueDist(f)))
     | (FRTypeNumeric, EvNumber(f)) => Some(FRValueNumber(f))
     | (FRTypeNumeric, EvDistribution(Symbolic(#Float(f)))) => Some(FRValueNumber(f))
-    | (FRTypeOption(v), _) => Some(FRValueOption(matchWithExpressionValue(v, r)))
     | (FRTypeLambda, EvLambda(f)) => Some(FRValueLambda(f))
     | (FRTypeArray(intendedType), EvArray(elements)) => {
         let el = elements->E.A2.fmap(matchWithExpressionValue(intendedType))
@@ -101,7 +97,6 @@ module FRType = {
     | FRValueDistOrNumber(FRValueNumber(n)) => EvNumber(n)
     | FRValueDistOrNumber(FRValueDist(n)) => EvDistribution(n)
     | FRValueDist(dist) => EvDistribution(dist)
-    | FRValueOption(Some(r)) => matchReverse(r)
     | FRValueArray(elements) => EvArray(elements->E.A2.fmap(matchReverse))
     | FRValueRecord(frValueRecord) => {
         let record =
@@ -113,7 +108,6 @@ module FRType = {
     | FRValueVariant(string) => EvString(string)
     }
 
-  // | FRValueOption(None) => break
   let matchWithExpressionValueArray = (inputs: array<t>, args: array<expressionValue>): option<
     array<frValue>,
   > => {
diff --git a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
index 8f3dea42..aa040fc2 100644
--- a/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
+++ b/packages/squiggle-lang/src/rescript/ReducerInterface/ReducerInterface_ExpressionValue.res
@@ -57,7 +57,7 @@ let rec toString = aValue =>
   | EvDistribution(dist) => GenericDist.toString(dist)
   | EvDate(date) => DateTime.Date.toString(date)
   | EvTimeDuration(t) => DateTime.Duration.toString(t)
-  | EvDeclaration(t) => "Declaration"
+  | EvDeclaration(d) => Declaration.toString(d, r => toString(EvLambda(r)))
   }
 and toStringRecord = aRecord => {
   let pairs =
@@ -128,6 +128,7 @@ type expressionValueType =
   | EvtSymbol
   | EvtDate
   | EvtTimeDuration
+  | EvtDeclaration
 
 type functionCallSignature = CallSignature(string, array<expressionValueType>)
 type functionDefinitionSignature =
@@ -147,6 +148,7 @@ let valueToValueType = value =>
   | EvSymbol(_) => EvtSymbol
   | EvDate(_) => EvtDate
   | EvTimeDuration(_) => EvtTimeDuration
+  | EvDeclaration(_) => EvtDeclaration
   }
 
 let functionCallToCallSignature = (functionCall: functionCall): functionCallSignature => {
@@ -168,6 +170,7 @@ let valueTypeToString = (valueType: expressionValueType): string =>
   | EvtSymbol => `Symbol`
   | EvtDate => `Date`
   | EvtTimeDuration => `Duration`
+  | EvtDeclaration => `Declaration`
   }
 
 let functionCallSignatureToString = (functionCallSignature: functionCallSignature): string => {
diff --git a/packages/squiggle-lang/src/rescript/Utility/Declaration.res b/packages/squiggle-lang/src/rescript/Utility/Declaration.res
index d26e1833..871dd580 100644
--- a/packages/squiggle-lang/src/rescript/Utility/Declaration.res
+++ b/packages/squiggle-lang/src/rescript/Utility/Declaration.res
@@ -19,6 +19,24 @@ module ContinuousTimeArg = {
   }
 }
 
+module Arg = {
+  let toString = (arg: arg) => {
+    switch arg {
+    | Float({min, max}) =>
+      `Float({min: ${E.Float.with2DigitsPrecision(min)}, max: ${E.Float.with2DigitsPrecision(
+          max,
+        )}})`
+    | Date({min, max}) =>
+      `Date({min: ${DateTime.Date.toString(min)}, max: ${DateTime.Date.toString(max)}})`
+    }
+  }
+}
+
 let make = (fn: 'a, args: array<arg>): declaration<'a> => {
   {fn: fn, args: args}
 }
+
+let toString = (r: declaration<'a>, fnToString): string => {
+  let args = r.args->E.A2.fmap(Arg.toString) |> E.A.joinWith(", ")
+  return`fn: ${fnToString(r.fn)}, args: [${args}]`
+}