diff --git a/pantograph/compiler.py b/pantograph/compiler.py
deleted file mode 100644
index 38469bf..0000000
--- a/pantograph/compiler.py
+++ /dev/null
@@ -1,21 +0,0 @@
-from dataclasses import dataclass
-
-@dataclass(frozen=True)
-class TacticInvocation:
-    """
-    One tactic invocation with the before/after goals extracted from Lean source
-    code.
-    """
-    before: str
-    after: str
-    tactic: str
-    used_constants: list[str]
-
-    @staticmethod
-    def parse(payload: dict):
-        return TacticInvocation(
-            before=payload["goalBefore"],
-            after=payload["goalAfter"],
-            tactic=payload["tactic"],
-            used_constants=payload.get('usedConstants', []),
-        )
diff --git a/pantograph/data.py b/pantograph/data.py
new file mode 100644
index 0000000..d2c0ae0
--- /dev/null
+++ b/pantograph/data.py
@@ -0,0 +1,69 @@
+from typing import Optional, Tuple
+from dataclasses import dataclass, field
+from pantograph.expr import GoalState
+
+@dataclass(frozen=True)
+class TacticInvocation:
+    """
+    One tactic invocation with the before/after goals extracted from Lean source
+    code.
+    """
+    before: str
+    after: str
+    tactic: str
+    used_constants: list[str]
+
+    @staticmethod
+    def parse(payload: dict):
+        return TacticInvocation(
+            before=payload["goalBefore"],
+            after=payload["goalAfter"],
+            tactic=payload["tactic"],
+            used_constants=payload.get('usedConstants', []),
+        )
+
+@dataclass(frozen=True)
+class CompilationUnit:
+
+    i_begin: int
+    i_end: int
+    messages: list[str] = field(default_factory=list)
+
+    invocations: Optional[list[TacticInvocation]] = None
+    # If `goal_state` is none, maybe error has occurred. See `messages`
+    goal_state: Optional[GoalState] = None
+    goal_src_boundaries: Optional[list[Tuple[int, int]]] = None
+
+    new_constants: Optional[list[str]] = None
+
+    @staticmethod
+    def parse(payload: dict, goal_state_sentinel=None):
+        i_begin = payload["boundary"][0]
+        i_end = payload["boundary"][1]
+        messages = payload["messages"]
+
+        if (invocation_payload := payload.get("invocations")) is not None:
+            invocations = [
+                TacticInvocation.parse(i) for i in invocation_payload
+            ]
+        else:
+            invocations = None
+
+        if (state_id := payload.get("goalStateId")) is not None:
+            goal_state = GoalState.parse_inner(int(state_id), payload["goals"], goal_state_sentinel)
+            goal_src_boundaries = payload["goalSrcBoundaries"]
+        else:
+            goal_state = None
+            goal_src_boundaries = None
+
+        new_constants = payload.get("newConstants")
+
+        return CompilationUnit(
+            i_begin,
+            i_end,
+            messages,
+            invocations,
+            goal_state,
+            goal_src_boundaries,
+            new_constants
+        )
diff --git a/pantograph/expr.py b/pantograph/expr.py
index 5c8bbc2..f616354 100644
--- a/pantograph/expr.py
+++ b/pantograph/expr.py
@@ -98,6 +98,7 @@ class GoalState:
         return GoalState(state_id, goals, _sentinel)
     @staticmethod
     def parse(payload: dict, _sentinel: list[int]):
+        assert _sentinel is not None
         return GoalState.parse_inner(payload["nextStateId"], payload["goals"], _sentinel)
 
     def __str__(self):
diff --git a/pantograph/server.py b/pantograph/server.py
index 3e9943d..bed7682 100644
--- a/pantograph/server.py
+++ b/pantograph/server.py
@@ -17,7 +17,7 @@ from pantograph.expr import (
     TacticCalc,
     TacticExpr,
 )
-from pantograph.compiler import TacticInvocation
+from pantograph.data import CompilationUnit
 
 def _get_proc_cwd():
     return Path(__file__).parent
@@ -173,7 +173,11 @@ class Server:
         if "error" in result:
             print(f"Cannot start goal: {expr}")
             raise ServerError(result["desc"])
-        return GoalState(state_id=result["stateId"], goals=[Goal.sentence(expr)], _sentinel=self.to_remove_goal_states)
+        return GoalState(
+            state_id=result["stateId"],
+            goals=[Goal.sentence(expr)],
+            _sentinel=self.to_remove_goal_states,
+        )
 
     def goal_tactic(self, state: GoalState, goal_id: int, tactic: Tactic) -> GoalState:
         """
@@ -231,7 +235,7 @@ class Server:
             raise ServerError(result["parseError"])
         return GoalState.parse(result, self.to_remove_goal_states)
 
-    def tactic_invocations(self, file_name: Union[str, Path]) -> tuple[list[str], list[TacticInvocation]]:
+    def tactic_invocations(self, file_name: Union[str, Path]) -> list[CompilationUnit]:
         """
         Collect tactic invocation points in file, and return them.
         """
@@ -244,26 +248,16 @@ class Server:
         if "error" in result:
             raise ServerError(result["desc"])
 
-        with open(file_name, 'rb') as f:
-            content = f.read()
-            units = [
-                content[unit["boundary"][0]:unit["boundary"][1]].decode('utf-8')
-                for unit in result['units']
-            ]
-            invocations = [
-                invocation
-                for unit in result['units']
-                for invocation in [TacticInvocation.parse(i) for i in unit['invocations']]
-            ]
-        return units, invocations
+        units = [CompilationUnit.parse(payload) for payload in result['units']]
+        return units
 
-    def load_sorry(self, command: str) -> list[GoalState | list[str]]:
+    def load_sorry(self, content: str) -> list[CompilationUnit]:
         """
         Executes the compiler on a Lean file. For each compilation unit, either
         return the gathered `sorry` s, or a list of messages indicating error.
         """
         result = self.run('frontend.process', {
-            'file': command,
+            'file': content,
             'invocations': False,
             "sorrys": True,
             "newConstants": False,
@@ -271,19 +265,11 @@ class Server:
         if "error" in result:
             raise ServerError(result["desc"])
 
-        def parse_unit(unit: dict):
-            state_id = unit.get("goalStateId")
-            if state_id is None:
-                # NOTE: `state_id` maybe 0.
-                # Maybe error has occurred
-                return unit["messages"]
-            state = GoalState.parse_inner(state_id, unit["goals"], self.to_remove_goal_states)
-            return state
-        states = [
-            parse_unit(unit) for unit in result['units']
+        units = [
+            CompilationUnit.parse(payload, goal_state_sentinel=self.to_remove_goal_states)
+            for payload in result['units']
         ]
-        return states
-
+        return units
 
 
 def get_version():
@@ -447,9 +433,9 @@ class TestServer(unittest.TestCase):
 
     def test_load_sorry(self):
         server = Server()
-        state0, = server.load_sorry("example (p: Prop): p → p := sorry")
-        if isinstance(state0, list):
-            print(state0)
+        unit, = server.load_sorry("example (p: Prop): p → p := sorry")
+        self.assertIsNotNone(unit.goal_state, f"{unit.messages}")
+        state0 = unit.goal_state
         self.assertEqual(state0.goals, [
             Goal(
                 [Variable(name="p", t="Prop")],