Refactor alignments & directions 📐

- Adds lang function
- Refactors execution context
- Adds StackChild and ParChild enums

1 files changed, 45 insertions, 0 deletions

diff --git a/src/library/lang.rs b/src/library/lang.rs
new file mode 100644
index 00000000..79015c7d
--- /dev/null
+++ b/src/library/lang.rs
@@ -0,0 +1,45 @@
+use super::*;
+
+/// `lang`: Configure the language.
+///
+/// # Positional parameters
+/// - Language: of type `string`. Has to be a valid ISO 639-1 code.
+///
+/// # Named parameters
+/// - Text direction: `dir`, of type `direction`, must be horizontal.
+///
+/// # Return value
+/// A template that configures language properties.
+///
+/// # Relevant types and constants
+/// - Type `direction`
+///   - `ltr`
+///   - `rtl`
+pub fn lang(ctx: &mut EvalContext, args: &mut FuncArgs) -> Value {
+    let iso = args.find::<String>(ctx).map(|s| s.to_ascii_lowercase());
+    let dir = args.get::<Spanned<Dir>>(ctx, "dir");
+
+    Value::template("lang", move |ctx| {
+        if let Some(iso) = &iso {
+            ctx.state.lang.dir = lang_dir(iso);
+        }
+
+        if let Some(dir) = dir {
+            if dir.v.axis() == SpecAxis::Horizontal {
+                ctx.state.lang.dir = dir.v;
+            } else {
+                ctx.diag(error!(dir.span, "must be horizontal"));
+            }
+        }
+
+        ctx.push_parbreak();
+    })
+}
+
+/// The default direction for the language identified by `iso`.
+fn lang_dir(iso: &str) -> Dir {
+    match iso {
+        "ar" | "he" | "fa" | "ur" | "ps" | "yi" => Dir::RTL,
+        "en" | "fr" | "de" | _ => Dir::LTR,
+    }
+}