Add standard `align` function and support right-alignment ➡️

1 files changed, 51 insertions, 0 deletions

diff --git a/src/library/align.rs b/src/library/align.rs
new file mode 100644
index 00000000..4b2ee8c3
--- /dev/null
+++ b/src/library/align.rs
@@ -0,0 +1,51 @@
+//! Alignment function.
+
+use super::prelude::*;
+use crate::layout::Alignment;
+
+
+/// Allows to align content in different ways.
+#[derive(Debug, PartialEq)]
+pub struct AlignFunc {
+    alignment: Alignment,
+    body: Option<SyntaxTree>,
+}
+
+impl Function for AlignFunc {
+    fn parse(header: &FuncHeader, body: Option<&str>, ctx: ParseContext)
+        -> ParseResult<Self> where Self: Sized {
+
+        if header.args.len() != 1 || !header.kwargs.is_empty() {
+            return err("expected exactly one positional argument specifying the alignment");
+        }
+
+        let alignment = if let Expression::Ident(ident) = &header.args[0] {
+            match ident.as_str() {
+                "left" => Alignment::Left,
+                "right" => Alignment::Right,
+                s => return err(format!("invalid alignment specifier: '{}'", s)),
+            }
+        } else {
+            return err(format!("expected alignment specifier, found: '{}'", header.args[0]));
+        };
+
+        let body = if let Some(body) = body {
+            Some(parse(body, ctx)?)
+        } else {
+            None
+        };
+
+        Ok(AlignFunc { alignment, body })
+    }
+
+    fn layout(&self, mut ctx: LayoutContext) -> LayoutResult<Option<Layout>> {
+        if let Some(body) = &self.body {
+            // Override the previous alignment and do the layouting.
+            ctx.space.alignment = self.alignment;
+            layout(body, ctx)
+                .map(|l| Some(Layout::Boxed(l)))
+        } else {
+            unimplemented!("context-modifying align func")
+        }
+    }
+}