Add CLI config file

book/src/cli-customization.md

@@ -35,10 +35,45 @@ Refer to your [package manager for details](./cli-installation.html#guidelines-f
 
 ## Customization
 
+### Configuration
+
+Numbats configuration file is called `config.toml`, and it needs to be placed in
+`<config-path>` described above (`~/.config/numbat/config.toml` on Linux). You
+can generate a default configuration by calling
+
+``` bash
+numbat --generate-config
+```
+
+The most important fields are:
+
+```
+[main]
+# Controls the welcome message. Can be "long", "short", or "off".
+intro-banner = "long"
+
+# Controls the prompt character(s) in the interactive terminal.
+prompt = ">>> "
+
+# Whether or not to pretty-print expressions before showing the result.
+# Can be "always", "never" or "auto". The latter uses pretty-printing
+# only in interactive mode.
+pretty-print = "auto"
+
+[exchange-rates]
+# When and if to load exchange rates from the European Central Bank for
+# currency conversions. Can be "on-startup" to always fetch exchange rates
+# in the background when the application is started. With "on-first-use",
+# Numbat only fetches exchange rates when they are needed. Exchange rate
+# fetching can also be disabled using "never". The latter will lead to
+# "unknown identifier" errors when a currency unit is being used.
+fetching-policy = "on-startup"
+```
+
 ### Custom functions, constants, units
 
 If you want to add custom functions, constants, or units to your default environment,
-create a `init.nbt` file in your config folder (e.g. `~/.config/numbat/init.nbt` on Linux).
+create a `init.nbt` file in your config folder (`~/.config/numbat/init.nbt` on Linux).
 
 ### Custom modules
 

numbat-cli/Cargo.toml

@@ -19,6 +19,8 @@ dirs = "5"
 numbat = { version = "1.7.0", path = "../numbat" }
 colored = "2"
 itertools = "0.11"
+toml = { version = "0.8.6", features = ["parse"] }
+serde = { version = "1.0.190", features = ["derive"] }
 
 [dependencies.clap]
 version = "4"

numbat-cli/src/config.rs

@@ -0,0 +1,76 @@
+use clap::ValueEnum;
+use serde::{Deserialize, Serialize};
+
+#[derive(Serialize, Deserialize, PartialEq, Eq, Default, Debug, Clone, Copy, ValueEnum)]
+#[serde(rename_all = "kebab-case")]
+pub enum IntroBanner {
+    #[default]
+    Long,
+    Short,
+    Off,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, ValueEnum, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum PrettyPrintMode {
+    Always,
+    Never,
+    Auto,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
+pub struct MainConfig {
+    pub intro_banner: IntroBanner,
+    pub prompt: String,
+    pub pretty_print: PrettyPrintMode,
+    pub load_prelude: bool,
+    pub load_user_init: bool,
+}
+
+impl Default for MainConfig {
+    fn default() -> Self {
+        Self {
+            prompt: ">>> ".to_owned(),
+            intro_banner: IntroBanner::default(),
+            pretty_print: PrettyPrintMode::Auto,
+            load_prelude: true,
+            load_user_init: true,
+        }
+    }
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Eq, Default)]
+#[serde(rename_all = "kebab-case")]
+pub enum ExchangeRateFetchingPolicy {
+    /// Always fetch exchange rates in the background when the application is started
+    #[default]
+    OnStartup,
+
+    /// Fetch exchange rates when a currency symbol is used
+    OnFirstUse,
+
+    /// Never fetch exchange rates
+    Never,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
+pub struct ExchangeRateConfig {
+    pub fetching_policy: ExchangeRateFetchingPolicy,
+}
+
+impl Default for ExchangeRateConfig {
+    fn default() -> Self {
+        Self {
+            fetching_policy: ExchangeRateFetchingPolicy::default(),
+        }
+    }
+}
+
+#[derive(Default, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case", default, deny_unknown_fields)]
+pub struct Config {
+    pub main: MainConfig,
+    pub exchange_rates: ExchangeRateConfig,
+}