vbs: let env.get report a missing symbol without raising an exception

This change is not useful per se, but prepares DEBUG-EVAL.

impls/vbs/env.vbs

@@ -41,8 +41,7 @@ Class Environment
 			If TypeName(objOuter) <> "Nothing" Then
 				Set varRet = objOuter.Find(varKey)
 			Else
-				Err.Raise vbObjectError, _
-					"Environment", "'" + varKey + "' not found"
+				Set varRet = Nothing
 			End If
 		End If
 
@@ -55,7 +54,11 @@ Class Environment
 		If objEnv Is objSelf Then
 			Set varRet = objBinds(varKey)
 		Else
+		  If TypeName(objEnv) <> "Nothing" Then
 			Set varRet = objEnv.Get(varKey)
+		  Else
+			Set varRet = Nothing
+		  End If
 		End If
 
 		Set [Get] = varRet

impls/vbs/step3_env.vbs

@@ -155,6 +155,10 @@ Function EvaluateAST(objCode, objEnv)
 	Select Case objCode.Type
 		Case TYPES.SYMBOL
 			Set varRet = objEnv.Get(objCode.Value)
+			if TypeName(varRet) = "Nothing" Then
+				Err.Raise vbObjectError, _
+					"EvaluateAST", "'" + objCode.Value + "' not found"
+			End If
 		Case TYPES.LIST
 			Err.Raise vbObjectError, _
 				"EvaluateAST", "Unexpect type."

impls/vbs/step4_if_fn_do.vbs

@@ -169,6 +169,10 @@ Function EvaluateAST(objCode, objEnv)
 	Select Case objCode.Type
 		Case TYPES.SYMBOL
 			Set varRet = objEnv.Get(objCode.Value)
+			if TypeName(varRet) = "Nothing" Then
+				Err.Raise vbObjectError, _
+					"EvaluateAST", "'" + objCode.Value + "' not found"
+			End If
 		Case TYPES.LIST
 			Err.Raise vbObjectError, _
 				"EvaluateAST", "Unexpect type."

impls/vbs/step5_tco.vbs

@@ -191,6 +191,10 @@ Function EvaluateAST(objCode, objEnv)
 	Select Case objCode.Type
 		Case TYPES.SYMBOL
 			Set varRet = objEnv.Get(objCode.Value)
+			if TypeName(varRet) = "Nothing" Then
+				Err.Raise vbObjectError, _
+					"EvaluateAST", "'" + objCode.Value + "' not found"
+			End If
 		Case TYPES.LIST
 			Err.Raise vbObjectError, _
 				"EvaluateAST", "Unexpect type."

impls/vbs/step6_file.vbs

@@ -219,6 +219,10 @@ Function EvaluateAST(objCode, objEnv)
 	Select Case objCode.Type
 		Case TYPES.SYMBOL
 			Set varRet = objEnv.Get(objCode.Value)
+			if TypeName(varRet) = "Nothing" Then
+				Err.Raise vbObjectError, _
+					"EvaluateAST", "'" + objCode.Value + "' not found"
+			End If
 		Case TYPES.LIST
 			Err.Raise vbObjectError, _
 				"EvaluateAST", "Unexpect type."

impls/vbs/step7_quote.vbs

@@ -342,6 +342,10 @@ Function EvaluateAST(objCode, objEnv)
 	Select Case objCode.Type
 		Case TYPES.SYMBOL
 			Set varRet = objEnv.Get(objCode.Value)
+			if TypeName(varRet) = "Nothing" Then
+				Err.Raise vbObjectError, _
+					"EvaluateAST", "'" + objCode.Value + "' not found"
+			End If
 		Case TYPES.LIST
 			Err.Raise vbObjectError, _
 				"EvaluateAST", "Unexpect type."

impls/vbs/step8_macros.vbs

@@ -359,6 +359,10 @@ Function EvaluateAST(objCode, objEnv)
 	Select Case objCode.Type
 		Case TYPES.SYMBOL
 			Set varRet = objEnv.Get(objCode.Value)
+			if TypeName(varRet) = "Nothing" Then
+				Err.Raise vbObjectError, _
+					"EvaluateAST", "'" + objCode.Value + "' not found"
+			End If
 		Case TYPES.LIST
 			Err.Raise vbObjectError, _
 				"EvaluateAST", "Unexpect type."

impls/vbs/step9_try.vbs

@@ -425,6 +425,10 @@ Function EvaluateAST(objCode, objEnv)
 	Select Case objCode.Type
 		Case TYPES.SYMBOL
 			Set varRet = objEnv.Get(objCode.Value)
+			if TypeName(varRet) = "Nothing" Then
+				Err.Raise vbObjectError, _
+					"EvaluateAST", "'" + objCode.Value + "' not found"
+			End If
 		Case TYPES.LIST
 			Err.Raise vbObjectError, _
 				"EvaluateAST", "Unexpect type."

impls/vbs/stepA_mal.vbs

@@ -426,6 +426,10 @@ Function EvaluateAST(objCode, objEnv)
 	Select Case objCode.Type
 		Case TYPES.SYMBOL
 			Set varRet = objEnv.Get(objCode.Value)
+			if TypeName(varRet) = "Nothing" Then
+				Err.Raise vbObjectError, _
+					"EvaluateAST", "'" + objCode.Value + "' not found"
+			End If
 		Case TYPES.LIST
 			Err.Raise vbObjectError, _
 				"EvaluateAST", "Unexpect type."