Implement escaping

README.md

@@ -52,7 +52,6 @@ This is an early work-in-progress. Follow [me on twitter](https://x.com/klntsky)
   - [x] return error throwing to the parser
   - [x] implement escaping
   - [x] `[:variable]` and `[:variable=some value]`
-  - [ ] `[!assertion]`
   - [x] `[:if ... :then ... :else ...]`
   - [x] `[$ meta-prompt]`
   - [x] `[:use module :param1=value1]`

docs/syntax.md

@@ -72,6 +72,20 @@ of prompt rewriting:
 
 Notice the double nesting of `[$` - the improved prompt will be fed back into an LLM.
 
+# Escaping
+
+Normally, you would not need escaping, e.g. `[:foo` will evaluate to `[:foo` as text. But if you want to specify a MetaPrompt expression literally, use `\` before the `[` character: `\[:foo]` will evaluate to `[:foo]` as text, without special meaning. You can escape `\` with another `\`, but only if it is positioned before a `[`:
+
+`\foo` → (text `\foo`)
+
+`\\` → (text `\\`)
+
+`\[:foo]` → (text `[:foo]`)
+
+`\\[:foo]` → (text `\\`) (variable `foo`)
+
+`\[some text` -> (text `[some text`) - note that in this case the `\` character disappears, although escaping does not happen because `[some text` not a special MetaPrompt construct.
+
 # Modules
 
 Every `.metaprompt` file is a function.

python/src/parse_metaprompt.py

@@ -17,11 +17,25 @@ def syntaxError(self, recognizer, offendingSymbol, line, column, msg, e):
         raise Exception(f"Syntax error at line {line}:{column} - {msg}")
 
 
-_pattern = r"\\([\[\\])"
+_pattern = r"\\([\[\\])(\[)?"
+
+
+def _escape_pattern(match):
+    first = match.group(1)
+    second = match.group(2)
+    if second is None:
+        if first == "\\":
+            return "\\\\"
+        elif first == "[":
+            return "["
+        else:
+            raise ValueError("Invariant violation: _escape_pattern")
+    else:
+        return match.group(1)
 
 
 def _process_escaping(string):
-    return re.sub(_pattern, lambda match: match.group(1), string)
+    return re.sub(_pattern, _escape_pattern, string)
 
 
 def _join_text_pieces(children):

python/tests/test_parser.py

@@ -26,6 +26,10 @@ def meta(exprs):
     return {"type": "meta", "exprs": exprs}
 
 
+def var(name):
+    return {"name": name, "type": "var"}
+
+
 def use(module_name, parameters):
     return {"type": "use", "module_name": module_name, "parameters": parameters}
 
@@ -65,14 +69,24 @@ def test_escaping_2():
     assert result["exprs"] == [t("[:foo]")]
 
 
+def test_escaping_2_1():
+    result = parse_metaprompt("\\\\[:foo]")
+    assert result["exprs"] == [t("\\\\"), var("foo")]
+
+
+def test_escaping_2_2():
+    result = parse_metaprompt("\\\\")
+    assert result["exprs"] == [t("\\\\")]
+
+
 def test_escaping_3():
     result = parse_metaprompt("\\[:foo")
     assert result["exprs"] == [t("[:foo")]
 
 
 def test_escaping_4():
     result = parse_metaprompt("\\\\[")
-    assert result["exprs"] == [t("\\[")]
+    assert result["exprs"] == [t("\\\\[")]
 
 
 def test_escaping_5():
@@ -92,7 +106,7 @@ def test_absence_of_comment():
 
 def test_meta():
     result = parse_metaprompt("[:test]")
-    assert result["exprs"] == [{"name": "test", "type": "var"}]
+    assert result["exprs"] == [var("test")]
 
 
 def test_meta_text():