From 07163fb627f5a43d48b9698bdeb1322279c3a379 Mon Sep 17 00:00:00 2001
From: ochafik <ochafik@google.com>
Date: Mon, 8 Apr 2024 20:10:15 +0100
Subject: [PATCH] grammars: add troubleshooting section to readme

---
 grammars/README.md | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/grammars/README.md b/grammars/README.md
index e1383fa5c..5c210de4c 100644
--- a/grammars/README.md
+++ b/grammars/README.md
@@ -89,3 +89,13 @@ This guide provides a brief overview. Check out the GBNF files in this directory
 ```
 ./main -m <model> --grammar-file grammars/some-grammar.gbnf -p 'Some prompt'
 ```
+
+## Troubleshooting
+
+Grammars currently have performance gotchas (see https://github.com/ggerganov/llama.cpp/issues/4218).
+
+### Efficient optional repetitions
+
+A common pattern is to allow repetitions of a pattern `x` up to N times.
+
+While semantically correct, the syntax `x? x? x?.... x?` (with N repetitions) will result in extremely slow inference. Instead, you can write `(x (x (x ... (x)?...)?)?)?` (w/ N-deep nesting)
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