isolate stack type definition

how:
  extract from methods implementation source into separate file

nimbus/vm2/stack.nim

@@ -7,17 +7,11 @@
 
 import
   chronicles, strformat, strutils, sequtils, macros, eth/common, nimcrypto,
-  ../errors, ../validation
+  ../errors, ../validation, ./stack_defs
 
 logScope:
   topics = "vm stack"
 
-type
-  Stack* = ref object of RootObj
-    values*: seq[StackElement]
-
-  StackElement = UInt256
-
 template ensureStackLimit: untyped =
   if len(stack.values) > 1023:
     raise newException(FullStack, "Stack limit reached")

nimbus/vm2/stack_defs.nim

@@ -0,0 +1,23 @@
+# Nimbus
+# Copyright (c) 2018 Status Research & Development GmbH
+# Licensed under either of
+#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
+#    http://www.apache.org/licenses/LICENSE-2.0)
+#  * MIT license ([LICENSE-MIT](LICENSE-MIT) or
+#    http://opensource.org/licenses/MIT)
+# at your option. This file may not be copied, modified, or distributed except
+# according to those terms.
+
+import
+  stint
+
+export
+  UInt256
+
+type
+  StackElement* = UInt256
+
+  Stack* = ref object of RootObj
+    values*: seq[StackElement]
+
+# End

nimbus/vm2/v2interpreter.nim

@@ -116,9 +116,10 @@ export
 
 
 import
+  ./stack_defs as sdf,
   ./stack as stk
 export
-  stk.Stack,
+  sdf.Stack,
   stk.`$`,
   stk.`[]`,
   stk.dup,

nimbus/vm2/v2types.nim

@@ -16,7 +16,7 @@ when defined(evmc_enabled):
 import
   tables, eth/common,
   options, json, sets,
-  ./v2memory, ./stack, ./code_stream,
+  ./v2memory, ./stack_defs, ./code_stream,
   ./interpreter/[v2gas_costs, v2opcode_values, v2forks],
   # TODO - will be hidden at a lower layer
   ../db/[db_chain, accounts_cache]