Prompt parser: account for empty field in alternating words syntax

modules/prompt_parser.py

@@ -20,7 +20,7 @@ prompt: (emphasized | scheduled | alternate | plain | WHITESPACE)*
         | "(" prompt ":" prompt ")"
         | "[" prompt "]"
 scheduled: "[" [prompt ":"] prompt ":" [WHITESPACE] NUMBER [WHITESPACE] "]"
-alternate: "[" prompt ("|" prompt)+ "]"
+alternate: "[" prompt ("|" [prompt])+ "]"
 WHITESPACE: /\s+/
 plain: /([^\\\[\]():|]|\\.)+/
 %import common.SIGNED_NUMBER -> NUMBER
@@ -53,6 +53,10 @@ def get_learned_conditioning_prompt_schedules(prompts, steps):
     [[3, '((a][:b:c '], [10, '((a][:b:c d']]
     >>> g("[a|(b:1.1)]")
     [[1, 'a'], [2, '(b:1.1)'], [3, 'a'], [4, '(b:1.1)'], [5, 'a'], [6, '(b:1.1)'], [7, 'a'], [8, '(b:1.1)'], [9, 'a'], [10, '(b:1.1)']]
+    >>> g("[fe|]male")
+    [[1, 'female'], [2, 'male'], [3, 'female'], [4, 'male'], [5, 'female'], [6, 'male'], [7, 'female'], [8, 'male'], [9, 'female'], [10, 'male']]
+    >>> g("[fe|||]male")
+    [[1, 'female'], [2, 'male'], [3, 'male'], [4, 'male'], [5, 'female'], [6, 'male'], [7, 'male'], [8, 'male'], [9, 'female'], [10, 'male']]
     """
 
     def collect_steps(steps, tree):
@@ -78,7 +82,8 @@ def get_learned_conditioning_prompt_schedules(prompts, steps):
                 before, after, _, when, _ = args
                 yield before or () if step <= when else after
             def alternate(self, args):
-                yield next(args[(step - 1)%len(args)])
+                args = ["" if not arg else arg for arg in args]
+                yield args[(step - 1) % len(args)]
             def start(self, args):
                 def flatten(x):
                     if type(x) == str: