compatibility to change environment at runtime

There will be changes in develop to change environment at runtime. This
fix provides compatibility. So that they can be merged easier.

packages/squiggle-lang/src/rescript/Reducer/Reducer_Dispatch/Reducer_Dispatch_BuiltIn.res

@@ -104,7 +104,7 @@ let callInternal = (
 
   let doDumpBindings = (continuation: nameSpace, value: internalExpressionValue) => {
     // let _ = Continuation.inspect(continuation, "doDumpBindings")
-    accessors.continuation = continuation
+    accessors.states.continuation = continuation
     value->Ok
   }
 

packages/squiggle-lang/src/rescript/Reducer/Reducer_Expression/Reducer_Expression.res

@@ -107,8 +107,9 @@ let reduceReturningBindings = (
   continuation: T.bindings,
   accessors: ProjectAccessorsT.t,
 ): (result<InternalExpressionValue.t, 'e>, T.bindings) => {
+  let states = accessors.states
   let result = reduceExpressionInProject(expression, continuation, accessors)
-  (result, accessors.continuation)
+  (result, states.continuation)
 }
 
 module BackCompatible = {

packages/squiggle-lang/src/rescript/Reducer/Reducer_Type/Reducer_Type_Compile.res

@@ -16,7 +16,7 @@ let ievFromTypeExpression = (
   Reducer_Expression.BackCompatible.parse(sourceCode)->Belt.Result.flatMap(expr => {
     let accessors = ProjectAccessorsT.identityAccessors
     let result = reducerFn(expr, Bindings.emptyBindings, accessors)
-    let nameSpace = accessors.continuation
+    let nameSpace = accessors.states.continuation
 
     switch result {
     | Ok(_) =>

packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject.res

@@ -138,7 +138,7 @@ module Private = {
   }
 
   let buildProjectAccessors = (this: t): ProjectAccessorsT.t => {
-    continuation: Bindings.emptyBindings,
+    states: {continuation: Bindings.emptyBindings},
     stdLib: getStdLib(this),
     environment: getEnvironment(this),
   }
@@ -149,9 +149,10 @@ module Private = {
     continuation: ProjectItem.T.continuation,
   ): unit => {
     let accessors = buildProjectAccessors(this)
+    let states = accessors.states
     let newItem = this->getItem(sourceId)->ProjectItem.run(continuation, accessors)
     Belt.Map.String.set(this["items"], sourceId, newItem)->T.Private.setFieldItems(this, _)
-    setContinuation(this, sourceId, accessors.continuation)
+    setContinuation(this, sourceId, states.continuation)
   }
 
   type runState = (ProjectItem.T.resultArgumentType, ProjectItem.T.continuation)

packages/squiggle-lang/src/rescript/ReducerProject/ReducerProject_ProjectAccessors_T.res

@@ -3,22 +3,38 @@ module Bindings = Reducer_Bindings
 module ExpressionT = Reducer_Expression_T
 module InternalExpressionValue = ReducerInterface_InternalExpressionValue
 
+type states = {mutable continuation: ProjectItemT.continuationArgumentType}
+
 type projectAccessors = {
   stdLib: Reducer_Bindings.t,
   environment: ExpressionT.environment,
-  mutable continuation: ProjectItemT.continuationArgumentType,
+  states: states,
 }
 
 type t = projectAccessors
 
 let identityAccessors: t = {
-  continuation: Bindings.emptyBindings,
+  // We need the states at the end of the runtime.
+  // Accessors can be modified but states will stay as the same pointer
+  states: {
+    continuation: Bindings.emptyBindings,
+  },
   stdLib: ReducerInterface_StdLib.internalStdLib,
   environment: InternalExpressionValue.defaultEnvironment,
 }
 
 let identityAccessorsWithEnvironment = (environment): t => {
-  continuation: Bindings.emptyBindings,
+  states: {
+    continuation: Bindings.emptyBindings,
+  },
   stdLib: ReducerInterface_StdLib.internalStdLib,
   environment: environment,
 }
+
+// to support change of environment in runtime
+let setEnvironment = (this: t, environment: ExpressionT.environment): t => {
+  {
+    ...this,
+    environment: environment,
+  }
+}