added alt/else, loops and other group shortcuts

src/group.typ

@@ -11,6 +11,36 @@
   ),)
 }
 
+#let _alt(desc, elmts, ..args) = {
+  let all-elmts = ()
+  all-elmts += elmts
+  let args = args.pos()
+  for i in range(0, args.len(), step: 2) {
+    let else-desc = args.at(i)
+    let else-elmts = args.at(i + 1, default: ())
+    all-elmts.push((
+      type: "else",
+      desc: else-desc
+    ))
+    all-elmts += else-elmts
+  }
+
+  return _grp("alt", desc: desc, type: "alt", all-elmts)
+}
+
+#let _loop(desc, min: none, max: auto, elmts) = {
+  let name = "loop"
+  if min != none {
+    if max == auto {
+      max = "*"
+    }
+    name += "(" + str(min) + "," + str(max) + ")"
+  }
+  _grp(name, desc: desc, type: "loop", elmts)
+}
+#let _opt(desc, elmts) = grp("opt", desc: desc, type: "opt", elmts)
+#let _break(desc, elmts) = grp("break", desc: desc, type: "break", elmts)
+
 #let render(x0, x1, y0, y1, group) = {
   let shapes = ()
   let name = text(group.name, weight: "bold")
@@ -50,5 +80,20 @@
     )
   }
 
+  return shapes
+}
+
+#let render-else(x0, x1, y, elmt) = {
+  let shapes = draw.line(
+    (x0, y),
+    (x1, y),
+    stroke: (dash: (2pt, 1pt), thickness: .5pt)
+  )
+  shapes += draw.content(
+    (x0, y),
+    text([\[#elmt.desc\]], weight: "bold", size: .8em),
+    anchor: "north-west",
+    padding: 3pt
+  )
   return shapes
 }