Another example

examples/resilient.py

@@ -0,0 +1,156 @@
+# A grammar based on
+# https://matklad.github.io/2023/05/21/resilient-ll-parsing-tutorial.html
+from parser import *
+
+
+@rule
+def File():
+    # TODO: Make lists easier
+    return _functions
+
+
+@rule
+def _functions():
+    return Function | (_functions + Function)
+
+
+@rule
+def Function():
+    return FN + NAME + ParamList + opt(ARROW + TypeExpr) + Block
+
+
+@rule
+def ParamList():
+    return LPAREN + opt(_parameters) + RPAREN
+
+
+@rule
+def _parameters():
+    # NOTE: The ungrammar in the reference does not talk about commas required between parameters
+    #       so this massages it to make them required. Commas are in the list not the param, which
+    #       is more awkward for processing but not terminally so.
+    return (Param + opt(COMMA)) | (Param + COMMA + _parameters)
+
+
+@rule
+def Param():
+    return NAME + COLON + TypeExpr
+
+
+@rule
+def TypeExpr():
+    return NAME
+
+
+@rule
+def Block():
+    return LCURLY + opt(_statements) + RCURLY
+
+
+@rule
+def _statements():
+    return Stmt | _statements + Stmt
+
+
+@rule
+def Stmt():
+    return StmtExpr | StmtLet | StmtReturn
+
+
+@rule
+def StmtExpr():
+    return Expr + SEMICOLON
+
+
+@rule
+def StmtLet():
+    return LET + NAME + EQUAL + Expr + SEMICOLON
+
+
+@rule
+def StmtReturn():
+    return RETURN + Expr + SEMICOLON
+
+
+@rule(error_name="expression")
+def Expr():
+    return ExprLiteral | ExprName | ExprParen | ExprBinary | ExprCall
+
+
+@rule
+def ExprLiteral():
+    return INT | TRUE | FALSE
+
+
+@rule
+def ExprName():
+    return NAME
+
+
+@rule
+def ExprParen():
+    return LPAREN + Expr + RPAREN
+
+
+@rule
+def ExprBinary():
+    return Expr + (PLUS | MINUS | STAR | SLASH) + Expr
+
+
+@rule
+def ExprCall():
+    return Expr + ArgList
+
+
+@rule
+def ArgList():
+    return LPAREN + opt(_arg_star) + RPAREN
+
+
+@rule
+def _arg_star():
+    # Again, a deviation from the original. See _parameters.
+    return (Expr + opt(COMMA)) | (Expr + COMMA + _arg_star)
+
+
+BLANKS = Terminal("BLANKS", Re.set(" ", "\t", "\r", "\n").plus())
+
+TRUE = Terminal("TRUE", "true")
+FALSE = Terminal("FALSE", "false")
+INT = Terminal("INT", Re.set(("0", "9")).plus())
+FN = Terminal("FN", "fn")
+ARROW = Terminal("ARROW", "->")
+COMMA = Terminal("COMMA", ",")
+LPAREN = Terminal("LPAREN", "(")
+RPAREN = Terminal("RPAREN", ")")
+LCURLY = Terminal("LCURLY", "{")
+RCURLY = Terminal("RCURLY", "}")
+COLON = Terminal("COLON", ":")
+SEMICOLON = Terminal("SEMICOLON", ";")
+LET = Terminal("LET", "let")
+EQUAL = Terminal("EQUAL", "=")
+RETURN = Terminal("RETURN", "return")
+PLUS = Terminal("PLUS", "+")
+MINUS = Terminal("MINUS", "-")
+STAR = Terminal("STAR", "*")
+SLASH = Terminal("SLASH", "/")
+
+NAME = Terminal(
+    "NAME",
+    Re.seq(
+        Re.set(("a", "z"), ("A", "Z"), "_"),
+        Re.set(("a", "z"), ("A", "Z"), ("0", "9"), "_").star(),
+    ),
+)
+
+LGrammar = Grammar(
+    name="L",
+    start=File,
+    trivia=[BLANKS],
+    # Need a little bit of disambiguation for the symbol involved.
+    precedence=[
+        (Assoc.LEFT, [PLUS, MINUS]),
+        (Assoc.LEFT, [STAR, SLASH]),
+        (Assoc.LEFT, [LPAREN]),
+    ],
+)