From e203e27407fc00da3c77f52fb0326fa183f6b4be Mon Sep 17 00:00:00 2001
From: John Doty <john@d0ty.me>
Date: Sat, 1 Jun 2024 05:42:40 -0700
Subject: [PATCH 1/2] Allow the grammar to specify a preference for a generator

Overridable, like start production
---
 grammar.py |  3 ++-
 harness.py |  7 +++----
 parser.py  | 13 +++++++++++--
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/grammar.py b/grammar.py
index 41c2064..1801bfd 100644
--- a/grammar.py
+++ b/grammar.py
@@ -1,7 +1,7 @@
 # This is an example grammar.
 import re
 
-from parser import Assoc, Grammar, Nothing, Terminal, rule, seq, Rule
+from parser import Assoc, GenerateLALR, GenerateLR1, Grammar, Nothing, Terminal, rule, seq, Rule
 
 ARROW = Terminal("Arrow")
 AS = Terminal("As")
@@ -81,6 +81,7 @@ class FineGrammar(Grammar):
                 #
                 (Assoc.NONE, [self.is_expression]),
             ],
+            generator=GenerateLALR,
         )
 
     @rule("File")
diff --git a/harness.py b/harness.py
index 268b6cd..acf48ff 100644
--- a/harness.py
+++ b/harness.py
@@ -258,11 +258,10 @@ class DynamicModule:
 
 
 class DynamicGrammarModule(DynamicModule):
-    def __init__(self, file_name, member_name, start_rule, generator):
+    def __init__(self, file_name, member_name, start_rule):
         super().__init__(file_name, member_name)
 
         self.start_rule = start_rule
-        self.generator = generator
 
     def _predicate(self, member) -> bool:
         if not super()._predicate(member):
@@ -274,7 +273,7 @@ class DynamicGrammarModule(DynamicModule):
         return False
 
     def _transform(self, value):
-        return value().build_table(start=self.start_rule, generator=self.generator)
+        return value().build_table(start=self.start_rule)
 
 
 class DynamicLexerModule(DynamicModule):
@@ -319,7 +318,7 @@ class Harness:
         self.max_entries = 0
 
         self.grammar_module = DynamicGrammarModule(
-            self.grammar_file, self.grammar_member, self.start_rule, generator=parser.GenerateLALR
+            self.grammar_file, self.grammar_member, self.start_rule
         )
 
         self.lexer_module = DynamicLexerModule(self.lexer_file, self.lexer_member)
diff --git a/parser.py b/parser.py
index 583d8bd..813d91d 100644
--- a/parser.py
+++ b/parser.py
@@ -1850,8 +1850,14 @@ class Grammar:
 
     _precedence: dict[str, typing.Tuple[Assoc, int]]
     _start: str
+    _generator: type[GenerateLR0]
 
-    def __init__(self, start: str, precedence: PrecedenceList | None = None):
+    def __init__(
+        self,
+        start: str,
+        precedence: PrecedenceList | None = None,
+        generator: type[GenerateLR0] = GenerateLALR,
+    ):
         if precedence is None:
             precedence = getattr(self, "precedence", [])
         assert precedence is not None
@@ -1870,6 +1876,7 @@ class Grammar:
 
         self._precedence = precedence_table
         self._start = start
+        self._generator = generator
 
     def generate_nonterminal_dict(
         self, start: str | None = None
@@ -1940,7 +1947,7 @@ class Grammar:
 
         return grammar, transparents
 
-    def build_table(self, start: str | None, generator=GenerateLALR):
+    def build_table(self, start: str | None, generator=None):
         """Construct a parse table for this grammar, starting at the named
         nonterminal rule.
         """
@@ -1948,6 +1955,8 @@ class Grammar:
             start = self._start
         desugared, transparents = self.desugar(start)
 
+        if generator is None:
+            generator = self._generator
         gen = generator(start, desugared, precedence=self._precedence, transparents=transparents)
         table = gen.gen_table()
         return table

From 03937e62e61d7da1f3d41a3f58c3def033391be4 Mon Sep 17 00:00:00 2001
From: John Doty <john@d0ty.me>
Date: Sat, 1 Jun 2024 05:57:16 -0700
Subject: [PATCH 2/2] Allow the generator to be a little more declarative

---
 grammar.py |  4 ++--
 parser.py  | 16 ++++++++++++++--
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/grammar.py b/grammar.py
index 1801bfd..1ecf61f 100644
--- a/grammar.py
+++ b/grammar.py
@@ -54,10 +54,11 @@ RSQUARE = Terminal("RightBracket")
 
 
 class FineGrammar(Grammar):
+    generator = GenerateLALR
+    start = "File"
 
     def __init__(self):
         super().__init__(
-            start="File",
             precedence=[
                 (Assoc.RIGHT, [EQUAL]),
                 (Assoc.LEFT, [OR]),
@@ -81,7 +82,6 @@ class FineGrammar(Grammar):
                 #
                 (Assoc.NONE, [self.is_expression]),
             ],
-            generator=GenerateLALR,
         )
 
     @rule("File")
diff --git a/parser.py b/parser.py
index 813d91d..4ad5683 100644
--- a/parser.py
+++ b/parser.py
@@ -1854,14 +1854,26 @@ class Grammar:
 
     def __init__(
         self,
-        start: str,
+        start: str | None = None,
         precedence: PrecedenceList | None = None,
-        generator: type[GenerateLR0] = GenerateLALR,
+        generator: type[GenerateLR0] | None = None,
     ):
+        if start is None:
+            start = getattr(self, "start", None)
+        if start is None:
+            raise ValueError(
+                "The default start rule must either be specified in the constructor or as an "
+                "attribute in the class."
+            )
+
         if precedence is None:
             precedence = getattr(self, "precedence", [])
         assert precedence is not None
 
+        if generator is None:
+            generator = getattr(self, "generator", GenerateLALR)
+        assert generator is not None
+
         precedence_table = {}
         for prec, (associativity, symbols) in enumerate(precedence):
             for symbol in symbols: