gallery/example1.typ

@@ -33,15 +33,38 @@ Alice <-- Bob: Another authentication Response
 #chronos.diagram({
   import chronos: *
   _seq("Alice", "Bob", comment: "Authentication Request")
-  _seq("Bob", "Alice", comment: "Authentication Failure")
 
-  _grp("My own label", desc: "My own label2", {
-    _seq("Alice", "Log", comment: "Log attack start")
-    _grp("loop", desc: "1000 times", {
-      _seq("Alice", "Bob", comment: "DNS Attack")
-    })
-    _seq("Alice", "Bob", comment: "Log attack end")
+  _alt(
+    "successful case", {
+      _seq("Bob", "Alice", comment: "Authentication Accepted")
+    },
+    "some kind of failure", {
+      _seq("Bob", "Alice", comment: "Authentication Failure")
+
+      _grp("My own label", desc: "My own label2", {
+        _seq("Alice", "Log", comment: "Log attack start")
+        _loop("1000 times", {
+          _seq("Alice", "Bob", comment: "DNS Attack")
+        })
+        _seq("Alice", "Log", comment: "Log attack end")
+      })
+    },
+    "Another type of failure", {
+      _seq("Bob", "Alice", comment: "Please repeat")
+    }
+  )
+})
+
+#chronos.diagram({
+  import chronos: *
+  _par("a", display-name: box(width: 1.5em, height: .5em), show-bottom: false)
+  _par("b", display-name: box(width: 1.5em, height: .5em), show-bottom: false)
+  _col("a", "b", width: 2cm)
+  _loop("a<1", min: 1, {
+    _seq("a", "b", end-tip: ">>")
+    _seq("b", "a", end-tip: ">>")
   })
+  _seq("a", "b", end-tip: ">>")
 })
 
 #chronos.diagram({

src/diagram.typ

@@ -185,7 +185,7 @@
 
   // Compute groups spans (horizontal)
   for (i, elmt) in elmts.enumerate() {
-    if elmt.type == "grp" {
+    if elmt.type == "grp" or elmt.type == "alt" {
       let (min-i, max-i) = get-group-span(participants, elmt)
       elmts.at(i).insert("min-i", min-i)
       elmts.at(i).insert("max-i", max-i)

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")
@@ -52,3 +82,18 @@
 
   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
+}

src/lib.typ

@@ -2,7 +2,7 @@
 #import "diagram.typ": diagram, from-plantuml, _gap, _evt, _col
 
 #import "sequence.typ": _seq
-#import "group.typ": _grp
+#import "group.typ": _grp, _loop, _alt, _opt, _break
 #import "participant.typ": _par
 #import "separator.typ": _sep
 #import "note.typ": _note

src/renderer.typ

@@ -242,6 +242,7 @@
 
   let draw-seq = sequence.render.with(pars-i, x-pos, participants)
   let draw-group = group.render.with()
+  let draw-else = group.render-else.with()
   let draw-sep = separator.render.with(x-pos)
   let draw-par = participant.render.with(x-pos)
   let draw-note = note.render.with(pars-i, x-pos)
@@ -283,6 +284,9 @@
         if g.at(1).max-i == elmt.max-i { g.at(3) += 1 }
         g
       })
+      if elmt.grp-type == "alt" {
+        elmt.insert("elses", ())
+      }
       groups.push((y, elmt, 0, 0))
       y -= m.height / 1pt
     
@@ -294,6 +298,21 @@
       let x1 = x-pos.at(group.max-i) + end-lvl * 10 + 20
       shapes += draw-group(x0, x1, start-y, y, group)
 
+      if group.grp-type == "alt" {
+        for (else-y, else-elmt) in group.elses {
+          shapes += draw-else(x0, x1, else-y, else-elmt)
+        }
+      }
+
+    // Alt's elses -> reserve space for label + store position
+    } else if elmt.type == "else" {
+      y -= Y-SPACE
+      let m = measure(text([\[#elmt.desc\]], weight: "bold", size: .8em))
+      groups.last().at(1).elses.push((
+        y, elmt
+      ))
+      y -= m.height / 1pt
+
     // Separator
     } else if elmt.type == "sep" {
       let shps