Develop a flow-style implementation of the sled example

In other usage, I discovered that it's rather confusing to have the parameters in the order that they were in. It feels better to have the fatal error after the regular error.

Cargo.lock

@@ -756,6 +756,14 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "error-training"
+version = "0.1.0"
+dependencies = [
+ "result-extended",
+ "thiserror",
+]
+
 [[package]]
 name = "etcetera"
 version = "0.8.0"
@@ -861,13 +869,6 @@ dependencies = [
  "miniz_oxide 0.7.1",
 ]
 
-[[package]]
-name = "flow"
-version = "0.1.0"
-dependencies = [
- "thiserror",
-]
-
 [[package]]
 name = "fluent"
 version = "0.16.0"
@@ -3119,6 +3120,13 @@ dependencies = [
  "winreg",
 ]
 
+[[package]]
+name = "result-extended"
+version = "0.1.0"
+dependencies = [
+ "thiserror",
+]
+
 [[package]]
 name = "rsa"
 version = "0.9.2"

Cargo.toml

@@ -7,8 +7,8 @@ members = [
     "cyberpunk-splash",
     "dashboard",
     "emseries",
+    "error-training",
     "file-service",
-    "flow",
     "fluent-ergonomics",
     "geo-types",
     "gm-control-panel",
@@ -17,7 +17,8 @@ members = [
     "kifu/core",
     "kifu/gtk",
     "memorycache",
+    "nom-training",
+    "result-extended",
     "screenplay",
     "sgf",
-    "nom-training",
 ]

build.sh

@@ -10,8 +10,8 @@ RUST_ALL_TARGETS=(
     "cyberpunk-splash"
     "dashboard"
     "emseries"
+    "error-training"
     "file-service"
-    "flow"
     "fluent-ergonomics"
     "geo-types"
     "gm-control-panel"
@@ -20,6 +20,8 @@ RUST_ALL_TARGETS=(
     "kifu-core"
     "kifu-gtk"
     "memorycache"
+    "nom-training"
+    "result-extended"
     "screenplay"
     "sgf"
 )

error-training/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "error-training"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[lib]
+name = "error_training"
+path = "src/lib.rs"
+
+[[bin]]
+name = "error-training"
+path = "src/main.rs"
+
+[dependencies]
+thiserror = { version = "1" }
+result-extended = { path = "../result-extended" }

error-training/src/flow.rs

@@ -0,0 +1,76 @@
+//! Flow-style error handling is conceptually the same as sled-style, but with macros to help
+//! out with the data structures. The result of a Flow-able operation is Flow<Value,
+//! FatalError, Error>.
+
+use super::*;
+use ::result_extended::{error, fatal, ok, return_error, return_fatal, Result};
+use std::collections::HashMap;
+
+pub struct DB(HashMap<String, i8>);
+
+impl DB {
+    pub fn new(lst: Vec<(String, i8)>) -> Self {
+        Self(lst.into_iter().collect::<HashMap<String, i8>>())
+    }
+
+    /// Retrieve a value from the database. Throw a fatal error with the "fail" key, but
+    /// otherwise return either the value or DatabaseError::NotFound.
+    ///
+    /// ```rust
+    /// use error_training::{*, flow::*};
+    /// use ::result_extended::Result;
+    ///
+    /// let db = DB::new(vec![("a".to_owned(), 15), ("b".to_owned(), 0)]);
+    /// assert_eq!(db.get("fail"), Result::Fatal(FatalError::DatabaseCorruption));
+    /// assert_eq!(db.get("a"), Result::Ok(15));
+    /// assert_eq!(db.get("c"), Result::Err(DatabaseError::NotFound));
+    /// ```
+    pub fn get(&self, key: &str) -> Result<i8, DatabaseError, FatalError> {
+        if key == "fail" {
+            fatal(FatalError::DatabaseCorruption)
+        } else {
+            // Result::from(self.0.get(key).copied().ok_or(DatabaseError::NotFound))
+            self.0
+                .get(key)
+                .copied()
+                .ok_or(DatabaseError::NotFound)
+                .into()
+        }
+    }
+}
+
+fn op(val: i8) -> std::result::Result<i8, MathError> {
+    if val as i32 + 120_i32 > (i8::MAX as i32) {
+        Err(MathError::ExceedsMaxint)
+    } else {
+        Ok(val + 120)
+    }
+}
+
+/// This function exists to test several of the major cases. This is where I will figure
+/// out how to handle everything and also have clean code.
+/// ```rust
+/// use error_training::{*, flow::*};
+/// use ::result_extended::Result;
+///
+/// let db = DB::new(vec![("a".to_owned(), 15), ("b".to_owned(), 0)]);
+/// assert_eq!(run_op(&db, "a"), Result::Ok(i8::MAX));
+/// assert_eq!(run_op(&db, "b"), Result::Ok(120));
+/// assert_eq!(run_op(&db, "c"), Result::Ok(0));
+/// assert_eq!(run_op(&db, "fail"), Result::Fatal(FatalError::DatabaseCorruption));
+/// ```
+///
+/// I have defined this function such that a database miss becomes a 0 and no operation
+/// will be performed on it. Since that is the only database error that can occur, this
+/// function can only return a `MathError` or a `FatalError`.
+pub fn run_op(db: &DB, key: &str) -> Result<i8, MathError, FatalError> {
+    let res = match return_fatal!(db.get(key)) {
+        Err(DatabaseError::NotFound) => Ok(0),
+        Ok(val) => op(val),
+    };
+
+    Result::from(res).or_else(|err| match err {
+        MathError::ExceedsMaxint => ok(i8::MAX),
+        _ => error(err),
+    })
+}

error-training/src/lib.rs

@@ -0,0 +1,51 @@
+use thiserror::Error;
+
+pub mod flow;
+pub mod sled;
+
+#[derive(Clone, Debug, Error, PartialEq)]
+pub enum FatalError {
+    #[error("Database corruption detected")]
+    DatabaseCorruption,
+}
+
+impl ::result_extended::FatalError for FatalError {}
+
+#[derive(Clone, Debug, Error, PartialEq)]
+pub enum MathError {
+    #[error("divide by zero is not defined")]
+    DivideByZero,
+
+    #[error("result exceeds maxint")]
+    ExceedsMaxint,
+
+    #[error("result exceeds minint")]
+    ExceedsMinint,
+}
+
+#[derive(Clone, Debug, Error, PartialEq)]
+pub enum DatabaseError {
+    #[error("value not found")]
+    NotFound,
+}
+
+#[derive(Clone, Debug, Error, PartialEq)]
+pub enum OperationError {
+    #[error("database error occurred: {0}")]
+    DatabaseError(DatabaseError),
+
+    #[error("math error occurred: {0}")]
+    MathError(MathError),
+}
+
+impl From<DatabaseError> for OperationError {
+    fn from(err: DatabaseError) -> Self {
+        Self::DatabaseError(err)
+    }
+}
+
+impl From<MathError> for OperationError {
+    fn from(err: MathError) -> Self {
+        Self::MathError(err)
+    }
+}

error-training/src/main.rs

@@ -0,0 +1,26 @@
+//! Error handling practice.
+//!
+//! The purpose of this crate is to demonstrate error handling in a couple of different scenarios
+//! so that I have clear templates to refer when doing development, instead of hand-waving or
+//! putting error handling off into the unspecified future.
+//!
+//! I am going to demonstrate error handling in the style of [Error Handling in a
+//! Correctness-Critical Rust Project | sled-rs.github.io](https://sled.rs/errors.html) and in my
+//! reformulation of it using Flow.
+//!
+//! I will also test out additional libraries in the same scenarios:
+//!
+//! - anyhow
+//!
+//! A database exists with some numbers. Mathmatical calculations will be performed on those
+//! numbers. Some calculations are invalid and should fail. In some cases, those should be reported
+//! to the user, and in other cases those can be recovered. Sometimes a calculation needs to be
+//! performed on a value that doesn't exist, which is also a failure. However, sometimes, the
+//! database will detect corruption, wich is fatal and should terminate the "app".
+//!
+//! In these scenarios, the "app" is a top-level function which runs the scenario. This particular
+//! app should never crash, just show where crashes would happen.
+
+fn main() {
+    println!("Hello, world!");
+}

error-training/src/sled.rs

@@ -0,0 +1,67 @@
+//! Sled-style error handling is based on Result<Result<Value, LocalError>, FatalError>.
+//! FatalErrors do not get resolved. LocalErrors get bubbled up until they can be handled.
+
+use super::*;
+use std::collections::HashMap;
+
+pub struct DB(HashMap<String, i8>);
+
+impl DB {
+    pub fn new(lst: Vec<(String, i8)>) -> Self {
+        Self(lst.into_iter().collect::<HashMap<String, i8>>())
+    }
+
+    /// Retrieve a value from the database. Throw a fatal error with the "fail" key, but
+    /// otherwise return either the value or DatabaseError::NotFound.
+    ///
+    /// ```rust
+    /// use error_training::{*, sled::*};
+    ///
+    /// let db = DB::new(vec![("a".to_owned(), 15), ("b".to_owned(), 0)]);
+    /// assert_eq!(db.get("fail"), Err(FatalError::DatabaseCorruption));
+    /// assert_eq!(db.get("a"), Ok(Ok(15)));
+    /// assert_eq!(db.get("c"), Ok(Err(DatabaseError::NotFound)));
+    /// ```
+    pub fn get(&self, key: &str) -> Result<Result<i8, DatabaseError>, FatalError> {
+        if key == "fail" {
+            Err(FatalError::DatabaseCorruption)
+        } else {
+            Ok(self.0.get(key).copied().ok_or(DatabaseError::NotFound))
+        }
+    }
+}
+
+fn op(val: i8) -> Result<i8, MathError> {
+    if val as i32 + 120_i32 > (i8::MAX as i32) {
+        Err(MathError::ExceedsMaxint)
+    } else {
+        Ok(val + 120)
+    }
+}
+
+/// This function exists to test several of the major cases. This is where I will figure out
+/// how to handle everything and also have clean code.
+/// ```rust
+/// use error_training::{*, sled::*};
+///
+/// let db = DB::new(vec![("a".to_owned(), 15), ("b".to_owned(), 0)]);
+/// assert_eq!(run_op(&db, "a"), Ok(Ok(i8::MAX)));
+/// assert_eq!(run_op(&db, "b"), Ok(Ok(120)));
+/// assert_eq!(run_op(&db, "c"), Ok(Ok(0)));
+/// assert_eq!(run_op(&db, "fail"), Err(FatalError::DatabaseCorruption));
+/// ```
+///
+/// I have defined this function such that a database miss becomes a 0 and no operation will be
+/// performed on it. Since that is the only database error that can occur, this function can
+/// only return a `MathError` or a `FatalError`.
+pub fn run_op(db: &DB, key: &str) -> Result<Result<i8, MathError>, FatalError> {
+    let res = match db.get(key)? {
+        Err(DatabaseError::NotFound) => Ok(0),
+        Ok(val) => op(val),
+    };
+
+    Ok(res.or_else(|err| match err {
+        MathError::ExceedsMaxint => Ok(127),
+        err => Err(err),
+    }))
+}

file-service/Cargo.toml

@@ -18,8 +18,6 @@ path = "src/main.rs"
 name = "auth-cli"
 path = "src/bin/cli.rs"
 
-[target.auth-cli.dependencies]
-
 [dependencies]
 base64ct            = { version = "1", features = [ "alloc" ] }
 build_html          = { version = "2" }

result-extended/Cargo.toml

@@ -1,5 +1,5 @@
 [package]
-name = "flow"
+name = "result-extended"
 version = "0.1.0"
 edition = "2021"
 license = "GPL-3.0-only"

result-extended/src/lib.rs

@@ -33,84 +33,84 @@ use std::{error::Error, fmt};
 /// statement.
 pub trait FatalError: Error {}
 
-/// Flow<A, FE, E> represents a return value that might be a success, might be a fatal error, or
+/// Result<A, FE, E> represents a return value that might be a success, might be a fatal error, or
 /// might be a normal handleable error.
-pub enum Flow<A, FE, E> {
+pub enum Result<A, E, FE> {
     /// The operation was successful
     Ok(A),
+    /// Ordinary errors. These should be handled and the application should recover gracefully.
+    Err(E),
     /// The operation encountered a fatal error. These should be bubbled up to a level that can
     /// safely shut the application down.
     Fatal(FE),
-    /// Ordinary errors. These should be handled and the application should recover gracefully.
-    Err(E),
 }
 
-impl<A, FE, E> Flow<A, FE, E> {
+impl<A, E, FE> Result<A, E, FE> {
     /// Apply an infallible function to a successful value.
-    pub fn map<B, O>(self, mapper: O) -> Flow<B, FE, E>
+    pub fn map<B, O>(self, mapper: O) -> Result<B, E, FE>
     where
         O: FnOnce(A) -> B,
     {
         match self {
-            Flow::Ok(val) => Flow::Ok(mapper(val)),
-            Flow::Fatal(err) => Flow::Fatal(err),
-            Flow::Err(err) => Flow::Err(err),
+            Result::Ok(val) => Result::Ok(mapper(val)),
+            Result::Err(err) => Result::Err(err),
+            Result::Fatal(err) => Result::Fatal(err),
         }
     }
 
     /// Apply a potentially fallible function to a successful value.
     ///
     /// Like `Result.and_then`, the mapping function can itself fail.
-    pub fn and_then<B, O>(self, handler: O) -> Flow<B, FE, E>
+    pub fn and_then<B, O>(self, handler: O) -> Result<B, E, FE>
     where
-        O: FnOnce(A) -> Flow<B, FE, E>,
+        O: FnOnce(A) -> Result<B, E, FE>,
     {
         match self {
-            Flow::Ok(val) => handler(val),
-            Flow::Fatal(err) => Flow::Fatal(err),
-            Flow::Err(err) => Flow::Err(err),
+            Result::Ok(val) => handler(val),
+            Result::Err(err) => Result::Err(err),
+            Result::Fatal(err) => Result::Fatal(err),
         }
     }
 
     /// Map a normal error from one type to another. This is useful for converting an error from
     /// one type to another, especially in re-throwing an underlying error. `?` syntax does not
-    /// work with `Flow`, so you will likely need to use this a lot.
-    pub fn map_err<F, O>(self, mapper: O) -> Flow<A, FE, F>
+    /// work with `Result`, so you will likely need to use this a lot.
+    pub fn map_err<F, O>(self, mapper: O) -> Result<A, F, FE>
     where
         O: FnOnce(E) -> F,
     {
         match self {
-            Flow::Ok(val) => Flow::Ok(val),
-            Flow::Fatal(err) => Flow::Fatal(err),
-            Flow::Err(err) => Flow::Err(mapper(err)),
+            Result::Ok(val) => Result::Ok(val),
+            Result::Err(err) => Result::Err(mapper(err)),
+            Result::Fatal(err) => Result::Fatal(err),
         }
     }
 
     /// Provide a function to use to recover from (or simply re-throw) an error.
-    pub fn or_else<O, F>(self, handler: O) -> Flow<A, FE, F>
+    pub fn or_else<O, F>(self, handler: O) -> Result<A, F, FE>
     where
-        O: FnOnce(E) -> Flow<A, FE, F>,
+        O: FnOnce(E) -> Result<A, F, FE>,
     {
         match self {
-            Flow::Ok(val) => Flow::Ok(val),
-            Flow::Fatal(err) => Flow::Fatal(err),
-            Flow::Err(err) => handler(err),
+            Result::Ok(val) => Result::Ok(val),
+            Result::Err(err) => handler(err),
+            Result::Fatal(err) => Result::Fatal(err),
         }
     }
 }
 
-/// Convert from a normal `Result` type to a `Flow` type. The error condition for a `Result` will
-/// be treated as `Flow::Err`, never `Flow::Fatal`.
-impl<A, FE, E> From<Result<A, E>> for Flow<A, FE, E> {
-    fn from(r: Result<A, E>) -> Self {
+/// Convert from a normal `Result` type to a `Result` type. The error condition for a `Result` will
+/// be treated as `Result::Err`, never `Result::Fatal`.
+impl<A, E, FE> From<std::result::Result<A, E>> for Result<A, E, FE> {
+    fn from(r: std::result::Result<A, E>) -> Self {
         match r {
-            Ok(val) => Flow::Ok(val),
-            Err(err) => Flow::Err(err),
+            Ok(val) => Result::Ok(val),
+            Err(err) => Result::Err(err),
         }
     }
 }
 
-impl<A, FE, E> fmt::Debug for Flow<A, FE, E>
+impl<A, E, FE> fmt::Debug for Result<A, E, FE>
 where
     A: fmt::Debug,
     FE: fmt::Debug,
@@ -118,14 +118,14 @@ where
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
-            Flow::Ok(val) => f.write_fmt(format_args!("Flow::Ok {:?}", val)),
-            Flow::Err(err) => f.write_fmt(format_args!("Flow::Err {:?}", err)),
-            Flow::Fatal(err) => f.write_fmt(format_args!("Flow::Fatal {:?}", err)),
+            Result::Ok(val) => f.write_fmt(format_args!("Result::Ok {:?}", val)),
+            Result::Err(err) => f.write_fmt(format_args!("Result::Err {:?}", err)),
+            Result::Fatal(err) => f.write_fmt(format_args!("Result::Fatal {:?}", err)),
         }
     }
 }
 
-impl<A, FE, E> PartialEq for Flow<A, FE, E>
+impl<A, E, FE> PartialEq for Result<A, E, FE>
 where
     A: PartialEq,
     FE: PartialEq,
@@ -133,27 +133,51 @@ where
 {
     fn eq(&self, rhs: &Self) -> bool {
         match (self, rhs) {
-            (Flow::Ok(val), Flow::Ok(rhs)) => val == rhs,
-            (Flow::Err(_), Flow::Err(_)) => true,
-            (Flow::Fatal(_), Flow::Fatal(_)) => true,
+            (Result::Ok(val), Result::Ok(rhs)) => val == rhs,
+            (Result::Err(_), Result::Err(_)) => true,
+            (Result::Fatal(_), Result::Fatal(_)) => true,
             _ => false,
         }
     }
 }
 
+impl<A, E: Error, FE: FatalError> From<std::result::Result<std::result::Result<A, E>, FE>>
+    for Result<A, E, FE>
+{
+    fn from(res: std::result::Result<std::result::Result<A, E>, FE>) -> Self {
+        match res {
+            Ok(Ok(v)) => ok(v),
+            Ok(Err(e)) => error(e),
+            Err(e) => fatal(e),
+        }
+    }
+}
+
+impl<A, E: Error, FE: FatalError> From<Result<A, E, FE>>
+    for std::result::Result<std::result::Result<A, E>, FE>
+{
+    fn from(res: Result<A, E, FE>) -> std::result::Result<std::result::Result<A, E>, FE> {
+        match res {
+            Result::Ok(v) => Ok(Ok(v)),
+            Result::Err(e) => Ok(Err(e)),
+            Result::Fatal(e) => Err(e),
+        }
+    }
+}
+
 /// Convenience function to create an ok value.
-pub fn ok<A, FE: FatalError, E: Error>(val: A) -> Flow<A, FE, E> {
-    Flow::Ok(val)
+pub fn ok<A, E: Error, FE: FatalError>(val: A) -> Result<A, E, FE> {
+    Result::Ok(val)
 }
 
 /// Convenience function to create an error value.
-pub fn error<A, FE: FatalError, E: Error>(err: E) -> Flow<A, FE, E> {
-    Flow::Err(err)
+pub fn error<A, E: Error, FE: FatalError>(err: E) -> Result<A, E, FE> {
+    Result::Err(err)
 }
 
 /// Convenience function to create a fatal value.
-pub fn fatal<A, FE: FatalError, E: Error>(err: FE) -> Flow<A, FE, E> {
-    Flow::Fatal(err)
+pub fn fatal<A, E: Error, FE: FatalError>(err: FE) -> Result<A, E, FE> {
+    Result::Fatal(err)
 }
 
 /// Return early from the current function if the value is a fatal error.
@@ -161,9 +185,9 @@ pub fn fatal<A, FE: FatalError, E: Error>(err: FE) -> Flow<A, FE, E> {
 macro_rules! return_fatal {
     ($x:expr) => {
         match $x {
-            Flow::Fatal(err) => return Flow::Fatal(err),
-            Flow::Err(err) => Err(err),
-            Flow::Ok(val) => Ok(val),
+            Result::Fatal(err) => return Result::Fatal(err),
+            Result::Err(err) => Err(err),
+            Result::Ok(val) => Ok(val),
         }
     };
 }
@@ -173,9 +197,9 @@ macro_rules! return_fatal {
 macro_rules! return_error {
     ($x:expr) => {
         match $x {
-            Flow::Ok(val) => val,
-            Flow::Err(err) => return Flow::Err(err),
-            Flow::Fatal(err) => return Flow::Fatal(err),
+            Result::Ok(val) => val,
+            Result::Err(err) => return Result::Err(err),
+            Result::Fatal(err) => return Result::Fatal(err),
         }
     };
 }
@@ -210,45 +234,45 @@ mod test {
 
     #[test]
     fn it_can_map_things() {
-        let success: Flow<i32, FatalError, Error> = ok(15);
+        let success: Result<i32, Error, FatalError> = ok(15);
         assert_eq!(ok(16), success.map(|v| v + 1));
     }
 
     #[test]
     fn it_can_chain_success() {
-        let success: Flow<i32, FatalError, Error> = ok(15);
+        let success: Result<i32, Error, FatalError> = ok(15);
         assert_eq!(ok(16), success.and_then(|v| ok(v + 1)));
     }
 
     #[test]
     fn it_can_handle_an_error() {
-        let failure: Flow<i32, FatalError, Error> = error(Error::Error);
+        let failure: Result<i32, Error, FatalError> = error(Error::Error);
         assert_eq!(
-            ok::<i32, FatalError, Error>(16),
+            ok::<i32, Error, FatalError>(16),
             failure.or_else(|_| ok(16))
         );
     }
 
     #[test]
     fn early_exit_on_fatal() {
-        fn ok_func() -> Flow<i32, FatalError, Error> {
-            let value = return_fatal!(ok::<i32, FatalError, Error>(15));
+        fn ok_func() -> Result<i32, Error, FatalError> {
+            let value = return_fatal!(ok::<i32, Error, FatalError>(15));
             match value {
                 Ok(_) => ok(14),
                 Err(err) => error(err),
             }
         }
 
-        fn err_func() -> Flow<i32, FatalError, Error> {
-            let value = return_fatal!(error::<i32, FatalError, Error>(Error::Error));
+        fn err_func() -> Result<i32, Error, FatalError> {
+            let value = return_fatal!(error::<i32, Error, FatalError>(Error::Error));
             match value {
                 Ok(_) => panic!("shouldn't have gotten here"),
                 Err(_) => ok(0),
             }
         }
 
-        fn fatal_func() -> Flow<i32, FatalError, Error> {
-            return_fatal!(fatal::<i32, FatalError, Error>(FatalError::FatalError));
+        fn fatal_func() -> Result<i32, Error, FatalError> {
+            let _ = return_fatal!(fatal::<i32, Error, FatalError>(FatalError::FatalError));
             panic!("failed to bail");
         }
 
@@ -259,19 +283,19 @@ mod test {
 
     #[test]
     fn it_can_early_exit_on_all_errors() {
-        fn ok_func() -> Flow<i32, FatalError, Error> {
-            let value = return_error!(ok::<i32, FatalError, Error>(15));
+        fn ok_func() -> Result<i32, Error, FatalError> {
+            let value = return_error!(ok::<i32, Error, FatalError>(15));
             assert_eq!(value, 15);
             ok(14)
         }
 
-        fn err_func() -> Flow<i32, FatalError, Error> {
-            return_error!(error::<i32, FatalError, Error>(Error::Error));
+        fn err_func() -> Result<i32, Error, FatalError> {
+            return_error!(error::<i32, Error, FatalError>(Error::Error));
             panic!("failed to bail");
         }
 
-        fn fatal_func() -> Flow<i32, FatalError, Error> {
-            return_error!(fatal::<i32, FatalError, Error>(FatalError::FatalError));
+        fn fatal_func() -> Result<i32, Error, FatalError> {
+            return_error!(fatal::<i32, Error, FatalError>(FatalError::FatalError));
             panic!("failed to bail");
         }