From d498ae8d6a4e84b13ccabe320fa5e35eba9218b1 Mon Sep 17 00:00:00 2001
From: "Zed A. Shaw" <zed.shaw@gmail.com>
Date: Thu, 19 Sep 2024 17:13:13 -0400
Subject: [PATCH] Now a working demo of FSM and DBC for the blog post.

---
 .gitignore         |  1 +
 python/dbc.py      | 23 +++++++++++++++++++
 python/dbc_test.py | 26 ++++++++++++++++++++++
 python/fsm.py      | 55 ++++++++++++++++++++++++++++++++++++++++++++++
 python/fsm_test.py |  8 +++++++
 status.txt         |  3 +++
 6 files changed, 116 insertions(+)
 create mode 100644 python/dbc.py
 create mode 100644 python/dbc_test.py
 create mode 100644 python/fsm.py
 create mode 100644 python/fsm_test.py
 create mode 100644 status.txt

diff --git a/.gitignore b/.gitignore
index bafeaa5..40d2c65 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,3 +14,4 @@ subprojects
 *.dll
 *~
 [0-9]*
+__pycache__
diff --git a/python/dbc.py b/python/dbc.py
new file mode 100644
index 0000000..e28051b
--- /dev/null
+++ b/python/dbc.py
@@ -0,0 +1,23 @@
+import traceback
+
+class DBCError(Exception): pass
+class CheckError(DBCError): pass
+class PreError(DBCError): pass
+class PostError(DBCError): pass
+class SentinelError(DBCError): pass
+
+def check(test, msg, cls=CheckError):
+    print(">>> ", msg)
+    traceback.print_stack(limit=-1)
+    if not test:
+        raise cls(msg)
+
+def pre(test, msg):
+    check(test, msg, PreError)
+
+def post(test, msg):
+    check(test, msg, PostError)
+
+def sentinel():
+    traceback.print_stack(limit=-1)
+    raise SentinelError()
diff --git a/python/dbc_test.py b/python/dbc_test.py
new file mode 100644
index 0000000..0e971a4
--- /dev/null
+++ b/python/dbc_test.py
@@ -0,0 +1,26 @@
+import dbc
+import traceback
+
+print("---- CHECK ---")
+try:
+    dbc.check(1 == 2, "Check Failed!")
+except dbc.CheckError as e:
+    print("Check failure:", e)
+
+print("---- SENTINEL ---")
+try:
+    dbc.sentinel()
+except dbc.SentinelError as e:
+    print("Sentinel failure:", e)
+
+print("---- PRECOND ---")
+try:
+    dbc.pre(1 == 2, "Pre Failed!")
+except dbc.PreError as e:
+    print("Pre condition failure: ", e)
+
+print("---- POSTCOND ---")
+try:
+    dbc.post(1 == 2, "Post Failed!")
+except dbc.PostError as e:
+    print("Post condition failure:", e)
diff --git a/python/fsm.py b/python/fsm.py
new file mode 100644
index 0000000..9f468c3
--- /dev/null
+++ b/python/fsm.py
@@ -0,0 +1,55 @@
+
+def START():
+    return LISTENING
+
+def LISTENING(event):
+    if event == "connect":
+        return CONNECTED
+    elif event == "error":
+        return LISTENING
+    else:
+        return ERROR
+
+def CONNECTED(event):
+    if event == "accept":
+        return ACCEPTED
+    elif event == "close":
+        return CLOSED
+    else:
+        return ERROR
+
+def ACCEPTED(event):
+    if event == "close":
+        return CLOSED
+    elif event == "read":
+        return READING(event)
+    elif event == "write":
+        return WRITING(event)
+    else:
+        return ERROR
+
+def READING(event):
+    if event == "read":
+        return READING
+    elif event == "write":
+        return WRITING(event)
+    elif event == "close":
+        return CLOSED
+    else:
+        return ERROR
+
+def WRITING(event):
+    if event == "read":
+        return READING(event)
+    elif event == "write":
+        return WRITING
+    elif event == "close":
+        return CLOSED
+    else:
+        return ERROR
+
+def CLOSED(event):
+    return LISTENING(event)
+
+def ERROR(event):
+    return ERROR
diff --git a/python/fsm_test.py b/python/fsm_test.py
new file mode 100644
index 0000000..0b076d1
--- /dev/null
+++ b/python/fsm_test.py
@@ -0,0 +1,8 @@
+import fsm
+
+state = fsm.START()
+script = ["connect", "accept", "read", "read", "write", "close", "connect"]
+
+for event in script:
+    print(event, ">>>", state)
+    state = state(event)
diff --git a/status.txt b/status.txt
new file mode 100644
index 0000000..e2c0508
--- /dev/null
+++ b/status.txt
@@ -0,0 +1,3 @@
+Welcome!
+
+Working on a blog post about Finite State Machines and Design-by-Contract.  Feel free to ask for advice about anything programming or art related.