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Diffstat (limited to 'aoc2023/build/packages/snag')
| -rw-r--r-- | aoc2023/build/packages/snag/LICENCE | 211 | ||||
| -rw-r--r-- | aoc2023/build/packages/snag/README.md | 81 | ||||
| -rw-r--r-- | aoc2023/build/packages/snag/gleam.toml | 16 | ||||
| -rw-r--r-- | aoc2023/build/packages/snag/include/snag_Snag.hrl | 1 | ||||
| -rw-r--r-- | aoc2023/build/packages/snag/src/snag.app.src | 8 | ||||
| -rw-r--r-- | aoc2023/build/packages/snag/src/snag.erl | 74 | ||||
| -rw-r--r-- | aoc2023/build/packages/snag/src/snag.gleam | 141 |
7 files changed, 532 insertions, 0 deletions
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result, + you may redistribute such product without providing attribution as would + otherwise be required by Sections 4(a), 4(b) and 4(d) of the License. diff --git a/aoc2023/build/packages/snag/README.md b/aoc2023/build/packages/snag/README.md new file mode 100644 index 0000000..aaedcf5 --- /dev/null +++ b/aoc2023/build/packages/snag/README.md @@ -0,0 +1,81 @@ +# Snag + +A Snag is a boilerplate-free ad-hoc error type. + +Use `Result(value, Snag)` (or the `snag.Result(value)` alias) in functions +that may fail. + +A low level message like "Unexpected status 401" or "No such file or +directory" can be confusing or difficult to debug, so use the `snag.context` +function to add extra contextual information. + +```gleam +import gleam/io +import my_app.{User} +import snag.{Result} + +pub fn log_in(user_id: Int) -> Result(User) { + try api_key = + my_app.read_file("api_key.txt") + |> snag.context("Could not load API key") + + try session_token = + user_id + |> my_app.create_session(api_key) + |> snag.context("Session creation failed") + + Ok(session_token) +} + +pub fn main() { + case log_in(42) { + Ok(session) -> io.println("Logged in!") + Error(snag) -> { + io.print(snag.pretty_print(snag)) + my_app.exit(1) + } + } +} +``` + +In this code when an error occurs within the `create_session` function an +error message like this is printed using the added contextual information: + +```text +error: Session creation failed + +cause: + 0: Unable to exchange token with authentication service + 1: Service authentication failed + 2: Unexpected HTTP status 401 +``` + +## When should I use Snag? + +Snag is useful in code where it must either pass or fail, and when it fails we +want good debugging information to print to the user. i.e. Command line +tools, data processing pipelines, etc. Here Snag provides a convenient way to +create errors with a reasonable amount of debugging information, without the +boilerplate of a custom error type. + +It is not suited to code where the application needs to make a decision about +what to do in the event of an error, such as whether to give up or to try +again. i.e. Libraries, web application backends, API clients, etc. In these +situations it is recommended to create a custom type for your errors as it +can be pattern matched on and have any additional detail added as fields. + +## Installation + +Add `snag` to your Gleam project + +``` +gleam add snag +``` + +## Prior art + +This library is inspired by the following projects: + +- Rust's [`anyhow`](https://github.com/dtolnay/anyhow) and + [`std::error::Error`](https://doc.rust-lang.org/std/error/trait.Error.html) +- Go's [`error`](https://golang.org/pkg/errors/). diff --git a/aoc2023/build/packages/snag/gleam.toml b/aoc2023/build/packages/snag/gleam.toml new file mode 100644 index 0000000..4f2d670 --- /dev/null +++ b/aoc2023/build/packages/snag/gleam.toml @@ -0,0 +1,16 @@ +name = "snag" +version = "0.2.1" +licences = ["Apache-2.0"] +description = "A boilerplate-free ad-hoc error type" + +repository = { type = "github", user = "gleam-experiments", repo = "snag" } +links = [ + { title = "Website", href = "https://gleam.run" }, + { title = "Sponsor", href = "https://github.com/sponsors/lpil" }, +] + +[dependencies] +gleam_stdlib = "~> 0.18" + +[dev-dependencies] +gleeunit = "~> 0.5" diff --git a/aoc2023/build/packages/snag/include/snag_Snag.hrl b/aoc2023/build/packages/snag/include/snag_Snag.hrl new file mode 100644 index 0000000..5d6614e --- /dev/null +++ b/aoc2023/build/packages/snag/include/snag_Snag.hrl @@ -0,0 +1 @@ +-record(snag, {issue :: binary(), cause :: list(binary())}). diff --git a/aoc2023/build/packages/snag/src/snag.app.src b/aoc2023/build/packages/snag/src/snag.app.src new file mode 100644 index 0000000..175e326 --- /dev/null +++ b/aoc2023/build/packages/snag/src/snag.app.src @@ -0,0 +1,8 @@ +{application, snag, [ + {vsn, "0.2.1"}, + {applications, [gleam_stdlib, + gleeunit]}, + {description, "A boilerplate-free ad-hoc error type"}, + {modules, [snag]}, + {registered, []} +]}. diff --git a/aoc2023/build/packages/snag/src/snag.erl b/aoc2023/build/packages/snag/src/snag.erl new file mode 100644 index 0000000..a07f242 --- /dev/null +++ b/aoc2023/build/packages/snag/src/snag.erl @@ -0,0 +1,74 @@ +-module(snag). +-compile([no_auto_import, nowarn_unused_vars]). + +-export([new/1, error/1, layer/2, context/2, pretty_print/1, line_print/1]). +-export_type([snag/0]). + +-type snag() :: {snag, binary(), list(binary())}. + +-spec new(binary()) -> snag(). +new(Issue) -> + {snag, Issue, []}. + +-spec error(binary()) -> {ok, any()} | {error, snag()}. +error(Issue) -> + {error, new(Issue)}. + +-spec layer(snag(), binary()) -> snag(). +layer(Snag, Issue) -> + {snag, Issue, [erlang:element(2, Snag) | erlang:element(3, Snag)]}. + +-spec context({ok, EXX} | {error, snag()}, binary()) -> {ok, EXX} | + {error, snag()}. +context(Result, Issue) -> + case Result of + {ok, _} -> + Result; + + {error, Snag} -> + {error, layer(Snag, Issue)} + end. + +-spec pretty_print_cause(list(binary())) -> gleam@string_builder:string_builder(). +pretty_print_cause(Cause) -> + _pipe = Cause, + _pipe@1 = gleam@list:index_map( + _pipe, + fun(Index, Line) -> + gleam@string:concat( + [<<" "/utf8>>, + gleam@int:to_string(Index), + <<": "/utf8>>, + Line, + <<"\n"/utf8>>] + ) + end + ), + gleam@string_builder:from_strings(_pipe@1). + +-spec pretty_print(snag()) -> binary(). +pretty_print(Snag) -> + Builder = gleam@string_builder:from_strings( + [<<"error: "/utf8>>, erlang:element(2, Snag), <<"\n"/utf8>>] + ), + gleam@string_builder:to_string(case erlang:element(3, Snag) of + [] -> + Builder; + + Cause -> + _pipe = Builder, + _pipe@1 = gleam@string_builder:append( + _pipe, + <<"\ncause:\n"/utf8>> + ), + gleam@string_builder:append_builder( + _pipe@1, + pretty_print_cause(Cause) + ) + end). + +-spec line_print(snag()) -> binary(). +line_print(Snag) -> + _pipe = [gleam@string:append(<<"error: "/utf8>>, erlang:element(2, Snag)) | + erlang:element(3, Snag)], + gleam@string:join(_pipe, <<" <- "/utf8>>). diff --git a/aoc2023/build/packages/snag/src/snag.gleam b/aoc2023/build/packages/snag/src/snag.gleam new file mode 100644 index 0000000..8d39537 --- /dev/null +++ b/aoc2023/build/packages/snag/src/snag.gleam @@ -0,0 +1,141 @@ +import gleam +import gleam/string_builder +import gleam/string +import gleam/list +import gleam/int + +/// A Snag is a boilerplate-free error type that can be used to track why an +/// error happened, though does not store as much detail on specific errors as a +/// custom error type would. +/// +/// It is useful in code where it must either pass or fail, and when it fails we +/// want good debugging information to print to the user. i.e. Command line +/// tools, data processing pipelines, etc. +/// +/// If it not suited to code where the application needs to make a decision about +/// what to do in the event of an error, such as whether to give up or to try +/// again. i.e. Libraries, web application backends, API clients, etc. +/// In these situations it is recommended to create a custom type for your errors +/// as it can be pattern matched on and have any additional detail added as +/// fields. +pub type Snag { + Snag(issue: String, cause: List(String)) +} + +/// A concise alias for a `Result` that uses a `Snag` as the error value. +pub type Result(t) = + gleam.Result(t, Snag) + +/// Create a new `Snag` with the given issue text. +/// +/// See also the `error` function for creating a `Snag` wrapped in a `Result`. +/// +/// # Example +/// +/// ```gleam +/// > new("Not enough credit") +/// > |> line_print +/// "error: Not enough credit" +/// ``` +pub fn new(issue: String) -> Snag { + Snag(issue: issue, cause: []) +} + +/// Create a new `Snag` wrapped in a `Result` with the given issue text. +/// +/// # Example +/// +/// ```gleam +/// > error("Not enough credit") +/// Error(new("Not enough credit")) +/// ``` +pub fn error(issue: String) -> Result(success) { + Error(new(issue)) +} + +/// Add additional contextual information to a `Snag`. +/// +/// See also the `context` function for adding contextual information to a `Snag` +/// wrapped in a `Result`. +/// +/// # Example +/// +/// ```gleam +/// > new("Not enough credit") +/// > |> layer("Unable to make purchase") +/// > |> line_print +/// "error: Unable to make purchase <- Not enough credit" +/// ``` +pub fn layer(snag: Snag, issue: String) -> Snag { + Snag(issue: issue, cause: [snag.issue, ..snag.cause]) +} + +/// Add additional contextual information to a `Snag` wrapped in a `Result`. +/// +/// # Example +/// +/// ```gleam +/// > error("Not enough credit") +/// > |> context("Unable to make purchase") +/// > |> result.map_error(line_print) +/// Error("error: Unable to make purchase <- Not enough credit") +/// ``` +pub fn context(result: Result(success), issue: String) -> Result(success) { + case result { + Ok(_) -> result + Error(snag) -> Error(layer(snag, issue)) + } +} + +/// Turn a snag into a multi-line string, optimised for readability. +/// +/// # Example +/// +/// ```gleam +/// > new("Not enough credit") +/// > |> layer("Unable to make purchase") +/// > |> layer("Character creation failed") +/// > |> pretty_print +/// "error: Character creation failed +/// +/// cause: +/// 0: Unable to make purchase +/// 1: Not enough credit +/// " +/// ``` +pub fn pretty_print(snag: Snag) -> String { + let builder = string_builder.from_strings(["error: ", snag.issue, "\n"]) + + string_builder.to_string(case snag.cause { + [] -> builder + cause -> + builder + |> string_builder.append("\ncause:\n") + |> string_builder.append_builder(pretty_print_cause(cause)) + }) +} + +fn pretty_print_cause(cause) { + cause + |> list.index_map(fn(index, line) { + string.concat([" ", int.to_string(index), ": ", line, "\n"]) + }) + |> string_builder.from_strings +} + +/// Turn a snag into a single-line string, optimised for compactness. This may be +/// useful for logging snags. +/// +/// # Example +/// +/// ```gleam +/// > new("Not enough credit") +/// > |> layer("Unable to make purchase") +/// > |> layer("Character creation failed") +/// > |> pretty_print +/// "error: Character creation failed <- Unable to make purchase <- Not enough credit" +/// ``` +pub fn line_print(snag: Snag) -> String { + [string.append("error: ", snag.issue), ..snag.cause] + |> string.join(" <- ") +} |