Update README with usage examples, module overview, and scope

README.md

@@ -1,61 +1,154 @@
 # orville-sqlite
 
-This library is intended to be a SQLite Haskell API similar in spirit to https://github.com/flipstone/orville/
+A type-safe SQLite API for Haskell, modeled after the [Flipstone Orville](https://github.com/flipstone/orville/) PostgreSQL library.
 
-The goal of this library is to provide a type safe approach to mapping Haskell types to SQLite data. We aim for type-safe queries and migrations.
+Maps Haskell data types to SQLite tables with compile-time schema guarantees.
 
-The Flipstone orville library is robust and deep. This library aspires to the same but realizes it's unlikely to get there anytime soon.
+## Status — MVP
 
-## Goal
+The MVP provides the core pipeline: define columns and record marshallers, auto-migrate schemas, and execute basic CRUD queries.
 
-This library intends to provide a similar API for describing the database schema and executing queries as the Flipstone Orville library.
+## Usage
-
-We will not port the PostgreSQL implementation directly but instead target a similar API.
-
-The APIs that concern us the most are:
-
-- Orville.PostgreSQL.Marshall.SqlMarshaller
-- Orville.PostgreSQL.AutoMigration as AutoMigration
-- Orville.PostgreSQL.Execution
-
-and even for those, we only what's strictly necessary to define a way to take a Haskell data type like
 
 ```haskell
+{-# LANGUAGE DataKinds #-}
 
-data Person =
+import Orville.SQLite
+
+data Person = Person
+  { personId :: Int64
+  , firstName :: Text
+  , lastName :: Text
+  , age :: Int64
+  }
+  deriving (Show, Eq)
+
+-- Column definitions (type-safe, parameterized by nullability)
+personIdField :: FieldDefinition 'NotNull Int64
+personIdField = integerField "id"
+
+firstNameField :: FieldDefinition 'NotNull Text
+firstNameField = textField "first_name"
+
+lastNameField :: FieldDefinition 'NotNull Text
+lastNameField = textField "last_name"
+
+ageField :: FieldDefinition 'NotNull Int64
+ageField = integerField "age"
+
+-- SqlMarshaller: maps the record to/from SQL columns
+personMarshaller :: SqlMarshaller Person Person
+personMarshaller =
   Person
-    { firstName :: Text
+    <$> marshallReadOnlyField personIdField  -- auto-increment PK
-    , lastName :: Text
+    <*> marshallField firstName firstNameField
-    , age :: Int
+    <*> marshallField lastName lastNameField
-    }
+    <*> marshallField age ageField
+
+-- TableDefinition ties a table name, primary key, and marshaller together
+personTable :: TableDefinition Int64 Person Person
+personTable =
+  mkTableDefinition "person" (primaryKey personId personIdField) personMarshaller
+
+main :: IO ()
+main = do
+  db <- openConnection "people.db"
+  withConnection db $ do
+    -- Auto-migrate: creates the table if it doesn't exist
+    autoMigrateSchema defaultOptions [schemaTable personTable []]
+
+    -- Insert
+    insertEntity personTable (Person 0 "Alice" "Smith" 30)
+    insertEntity personTable (Person 0 "Bob"   "Jones" 25)
+
+    -- Query by primary key
+    mAlice <- findEntity personTable 1
+    -- mAlice = Just (Person 1 "Alice" "Smith" 30)
+
+    -- Find all
+    all <- findAll personTable
+    -- all = [Person 1 "Alice" "Smith" 30, Person 2 "Bob" "Jones" 25]
+
+    -- Update
+    updateEntity personTable (Person 1 "Alice" "Jones" 31)
+
+    -- Delete
+    deleteEntity personTable 2
+
+    pure ()
+  closeConnection db
 ```
 
-and map it to a table of schema
+The above creates this table:
 
 ```sql
-CREATE TABLE person (
+CREATE TABLE IF NOT EXISTS person (
-    first_name VARCHAR(100) NOT NULL,
+  age INTEGER NOT NULL,
-    last_name  VARCHAR(100) NOT NULL,
+  last_name TEXT NOT NULL,
-    age        INT
+  first_name TEXT NOT NULL,
+  id INTEGER PRIMARY KEY
 );
 ```
 
-and then give us an API for marshalling that Haskell type to that table definition
+## Modules
 
-then using that marshaller we should have APIs that can;
+| Module | Purpose |
+|--------|---------|
+| `Orville.SQLite` | Top-level re-exports |
+| `Orville.SQLite.Monad` | `OrvilleM` reader monad and connection management |
+| `Orville.SQLite.SqlType` | Type encoding/decoding for SQLite storage classes |
+| `Orville.SQLite.FieldDefinition` | GADT column definitions with `NotNull`/`Nullable` |
+| `Orville.SQLite.SqlMarshaller` | GADT record-to-table mapping (applicative syntax) |
+| `Orville.SQLite.TableDefinition` | `PrimaryKey` and `mkTableDefinition` |
+| `Orville.SQLite.AutoMigration` | Schema introspection via `PRAGMA table_info`, DDL generation |
+| `Orville.SQLite.Execution` | `insertEntity`, `findEntity`, `findAll`, `updateEntity`, `deleteEntity` |
 
-- create the table if it does not exist
+## Feature Coverage
-- alter the table to match the schema if the table does exist but its columns don't match
-- query the table and retrieve Person values
-- insert Person values into the table
-- update the table from Person values.
 
-## Development environment
+### Included (MVP)
 
-The development environment should be entirely inside of Docker - no local
+- `FieldDefinition` with `NotNull`/`Nullable` type parameters
-tools should be installed on the machine directly. use the `hs` wrapper script
+- `SqlMarshaller` GADT with `marshallField`, `marshallReadOnlyField`, `marshallMaybe`
-to execute Haskell tooling inside of Docker.
+- `TableDefinition` with single-column primary keys
+- `AutoMigration`: create tables, add nullable columns, drop columns (explicit opt-in), dry-run
+- `Execution`: insert, find-by-PK, find-all, update, delete
+- In-memory databases (`:memory:`) and file-based databases
 
-## Base SQLite library
+### Not yet implemented
 
-Our base library for interacting with SQLite should be direct-sqlite - https://github.com/IreneKnapp/direct-sqlite
+- Foreign keys and composite primary keys
+- Table indexes
+- Plans (N+1 query prevention via `Plan`)
+- Batch operations
+- Upsert (`upsertEntity`)
+- `findEntitiesBy` (filtering on non-PK columns)
+- `updateFields` (partial update)
+- Raw SQL execution (`executeAndDecode`)
+- Nested record marshalling and `prefixMarshaller`
+- `AnnotatedSqlMarshaller`
+- `SyntheticField`
+- Connection pooling
+
+## Development
+
+All tooling runs inside Docker via the `./hs` wrapper. No local Haskell installation needed.
+
+```bash
+./hs stack build       # build
+./hs stack test        # run tests (53 tests)
+./hs stack ghci        # REPL
+./hs fourmolu -i src/  # format
+```
+
+Or use the convenience scripts:
+
+```bash
+./scripts/build         # build with pedantic
+./scripts/test          # run tests
+```
+
+### Dependencies
+
+- GHC 9.10.3
+- [direct-sqlite](https://github.com/IreneKnapp/direct-sqlite) — low-level FFI binding to SQLite
+- `text`, `bytestring`, `mtl`