From 70f00d1a1e2e82582c576605d7f3e10c01345511 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Thu, 3 Jan 2019 13:49:37 -0800
Subject: [PATCH] Give immediate tokens higher implicit precedence than other
 tokens

---
 src/build_tables/token_conflicts.rs           | 17 ++++++++---------
 src/grammars.rs                               |  2 +-
 src/prepare_grammar/expand_tokens.rs          | 16 +++++++++++-----
 src/prepare_grammar/extract_simple_aliases.rs |  6 +++---
 4 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/src/build_tables/token_conflicts.rs b/src/build_tables/token_conflicts.rs
index 18a80484..91edadec 100644
--- a/src/build_tables/token_conflicts.rs
+++ b/src/build_tables/token_conflicts.rs
@@ -2,6 +2,7 @@ use crate::build_tables::item::LookaheadSet;
 use crate::grammars::LexicalGrammar;
 use crate::nfa::{CharacterSet, NfaCursor};
 use hashbrown::HashSet;
+use std::cmp::Ordering;
 use std::fmt;
 
 #[derive(Clone, Debug, Default, PartialEq, Eq)]
@@ -71,16 +72,14 @@ impl<'a> TokenConflictMap<'a> {
             return false;
         }
 
-        match (
-            grammar.variables[left.1].is_string,
-            grammar.variables[right.1].is_string,
-        ) {
-            (true, false) => return true,
-            (false, true) => return false,
-            _ => {}
+        match grammar.variables[left.1]
+            .implicit_precedence
+            .cmp(&grammar.variables[right.1].implicit_precedence)
+        {
+            Ordering::Less => false,
+            Ordering::Greater => true,
+            Ordering::Equal => left.1 < right.1,
         }
-
-        left.0 < right.0
     }
 }
 
diff --git a/src/grammars.rs b/src/grammars.rs
index 7f587a8c..f82d6b02 100644
--- a/src/grammars.rs
+++ b/src/grammars.rs
@@ -36,7 +36,7 @@ pub(crate) struct InputGrammar {
 pub(crate) struct LexicalVariable {
     pub name: String,
     pub kind: VariableType,
-    pub is_string: bool,
+    pub implicit_precedence: i32,
     pub start_state: u32,
 }
 
diff --git a/src/prepare_grammar/expand_tokens.rs b/src/prepare_grammar/expand_tokens.rs
index 61b1897c..6520c432 100644
--- a/src/prepare_grammar/expand_tokens.rs
+++ b/src/prepare_grammar/expand_tokens.rs
@@ -14,11 +14,17 @@ struct NfaBuilder {
     precedence_stack: Vec<i32>,
 }
 
-fn is_string(rule: &Rule) -> bool {
+fn get_implicit_precedence(rule: &Rule) -> i32 {
     match rule {
-        Rule::String(_) => true,
-        Rule::Metadata { rule, .. } => is_string(rule),
-        _ => false,
+        Rule::String(_) => 1,
+        Rule::Metadata { rule, params } => {
+            if params.is_main_token {
+                get_implicit_precedence(rule) + 2
+            } else {
+                get_implicit_precedence(rule)
+            }
+        }
+        _ => 0,
     }
 }
 
@@ -67,7 +73,7 @@ pub(crate) fn expand_tokens(mut grammar: ExtractedLexicalGrammar) -> Result<Lexi
         variables.push(LexicalVariable {
             name: variable.name,
             kind: variable.kind,
-            is_string: is_string(&variable.rule),
+            implicit_precedence: get_implicit_precedence(&variable.rule),
             start_state: builder.nfa.last_state_id(),
         });
     }
diff --git a/src/prepare_grammar/extract_simple_aliases.rs b/src/prepare_grammar/extract_simple_aliases.rs
index ee748f5d..aa8b3f77 100644
--- a/src/prepare_grammar/extract_simple_aliases.rs
+++ b/src/prepare_grammar/extract_simple_aliases.rs
@@ -137,19 +137,19 @@ mod tests {
                 LexicalVariable {
                     name: "t1".to_string(),
                     kind: VariableType::Anonymous,
-                    is_string: true,
+                    implicit_precedence: 0,
                     start_state: 0,
                 },
                 LexicalVariable {
                     name: "t2".to_string(),
                     kind: VariableType::Anonymous,
-                    is_string: true,
+                    implicit_precedence: 0,
                     start_state: 0,
                 },
                 LexicalVariable {
                     name: "t3".to_string(),
                     kind: VariableType::Anonymous,
-                    is_string: true,
+                    implicit_precedence: 0,
                     start_state: 0,
                 }
             ],