Make a trait for lookahead

lalrpop/src/lr1/core/mod.rs

@@ -3,34 +3,34 @@
 use collections::Map;
 use grammar::repr::*;
 use itertools::Itertools;
-use std::fmt::{Debug, Formatter, Error};
+use std::fmt::{Debug, Display, Formatter, Error};
 use std::rc::Rc;
 use util::Prefix;
 
-use super::lookahead::Token;
+use super::lookahead::*;
 
 #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
-pub struct Item<'grammar, L: Clone> {
+pub struct Item<'grammar, L: Lookahead> {
     pub production: &'grammar Production,
     /// the dot comes before `index`, so `index` would be 1 for X = A (*) B C
     pub index: usize,
     pub lookahead: L,
 }
 
-pub type LR0Item<'grammar> = Item<'grammar, ()>;
+pub type LR0Item<'grammar> = Item<'grammar, Nil>;
 
 pub type LR1Item<'grammar> = Item<'grammar, Token>;
 
-impl<'grammar> Item<'grammar, ()> {
+impl<'grammar> Item<'grammar, Nil> {
     #[cfg(test)]
     pub fn lr0(production: &'grammar Production,
                index: usize)
                -> Self {
-        Item { production: production, index: index, lookahead: () }
+        Item { production: production, index: index, lookahead: Nil }
     }
 }
 
-impl<'grammar, L: Clone> Item<'grammar, L> {
+impl<'grammar, L: Lookahead> Item<'grammar, L> {
     pub fn prefix(&self) -> &'grammar [Symbol] {
         &self.production.symbols[..self.index]
     }
@@ -53,7 +53,7 @@ impl<'grammar, L: Clone> Item<'grammar, L> {
     }
 
     pub fn to_lr0(&self) -> LR0Item<'grammar> {
-        Item { production: self.production, index: self.index, lookahead: () }
+        Item { production: self.production, index: self.index, lookahead: Nil }
     }
 
     pub fn can_shift(&self) -> bool {
@@ -88,15 +88,15 @@ impl<'grammar, L: Clone> Item<'grammar, L> {
 pub struct StateIndex(pub usize);
 
 #[derive(Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
-pub struct Items<'grammar, L: Clone> {
+pub struct Items<'grammar, L: Lookahead> {
     pub vec: Rc<Vec<Item<'grammar, L>>>
 }
 
-pub type LR0Items<'grammar> = Items<'grammar, ()>;
+pub type LR0Items<'grammar> = Items<'grammar, Nil>;
 pub type LR1Items<'grammar> = Items<'grammar, Token>;
 
 #[derive(Debug)]
-pub struct State<'grammar, L: Clone> {
+pub struct State<'grammar, L: Lookahead> {
     pub index: StateIndex,
     pub items: Items<'grammar, L>,
     pub tokens: Map<Token, Action<'grammar>>,
@@ -104,7 +104,7 @@ pub struct State<'grammar, L: Clone> {
     pub gotos: Map<NonterminalString, StateIndex>,
 }
 
-pub type LR0State<'grammar> = State<'grammar, ()>;
+pub type LR0State<'grammar> = State<'grammar, Nil>;
 pub type LR1State<'grammar> = State<'grammar, Token>;
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -131,24 +131,18 @@ pub struct TableConstructionError<'grammar> {
     pub states: Vec<LR1State<'grammar>>,
 }
 
-impl<'grammar, L: Clone+Debug> Debug for Item<'grammar, L> {
+impl<'grammar, L: Lookahead> Debug for Item<'grammar, L> {
     fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
-        let mut lookahead_debug = format!("{:?}", self.lookahead);
-        if lookahead_debug != "()" {
-            lookahead_debug = format!(" [{}]", lookahead_debug);
-        } else {
-            lookahead_debug = format!("");
-        }
-
-        write!(fmt, "{} ={} (*){}{}",
+        try!(write!(fmt, "{} ={} (*){}",
                     self.production.nonterminal,
                     Prefix(" ", &self.production.symbols[..self.index]),
-               Prefix(" ", &self.production.symbols[self.index..]),
-               lookahead_debug)
+                    Prefix(" ", &self.production.symbols[self.index..])));
+
+        self.lookahead.fmt_as_item_suffix(fmt)
     }
 }
 
-impl Debug for Token {
+impl Display for Token {
     fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
         match *self {
             Token::EOF => write!(fmt, "EOF"),
@@ -157,13 +151,19 @@ impl Debug for Token {
     }
 }
 
+impl Debug for Token {
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        write!(fmt, "{}", self)
+    }
+}
+
 impl Debug for StateIndex {
     fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
         write!(fmt, "S{}", self.0)
     }
 }
 
-impl<'grammar, L: Clone> State<'grammar, L> {
+impl<'grammar, L: Lookahead> State<'grammar, L> {
     /// Returns the set of symbols which must appear on the stack to
     /// be in this state. This is the *maximum* prefix of any item,
     /// basically.

lalrpop/src/lr1/lookahead.rs

@@ -2,6 +2,19 @@ use bit_set::{self, BitSet};
 use std::fmt::{Debug, Formatter, Error};
 use grammar::repr::*;
 
+pub trait Lookahead: Clone + Debug + PartialEq + Eq + PartialOrd + Ord {
+    fn fmt_as_item_suffix(&self, fmt: &mut Formatter) -> Result<(), Error>;
+}
+
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Nil;
+
+impl Lookahead for Nil {
+    fn fmt_as_item_suffix(&self, _fmt: &mut Formatter) -> Result<(), Error> {
+        Ok(())
+    }
+}
+
 /// I have semi-arbitrarily decided to say that a "token" is either
 /// one of the terminals of our language, or else the pseudo-symbol
 /// EOF that represents "end of input".
@@ -11,6 +24,12 @@ pub enum Token {
     Terminal(TerminalString),
 }
 
+impl Lookahead for Token {
+    fn fmt_as_item_suffix(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        write!(fmt, " [{}]", self)
+    }
+}
+
 impl Token {
     pub fn unwrap_terminal(self) -> TerminalString {
         match self {

lalrpop/src/lr1/trace/shift/test.rs

@@ -43,7 +43,7 @@ pub Ty: () = {
     //     Ty = Ty -> Ty (*) (reduce)
 
     assert!(conflict.production.symbols.len() == 3);
-    let item = Item { production: conflict.production, index: 1, lookahead: () };
+    let item = Item::lr0(conflict.production, 1);
     println!("item={:?}", item);
     let tracer = Tracer::new(&grammar, &states);
     let graph = tracer.backtrace_shift(conflict.state, item);

lalrpop/src/lr1/trace/trace_graph/mod.rs

@@ -1,5 +1,6 @@
 use collections::{Map, map};
 use lr1::core::*;
+use lr1::lookahead::*;
 use lr1::example::*;
 use grammar::repr::*;
 use petgraph::{EdgeDirection, Graph};
@@ -102,7 +103,7 @@ impl<'grammar> Into<TraceGraphNode<'grammar>> for NonterminalString {
     }
 }
 
-impl<'grammar, L: Clone> Into<TraceGraphNode<'grammar>> for Item<'grammar, L> {
+impl<'grammar, L: Lookahead> Into<TraceGraphNode<'grammar>> for Item<'grammar, L> {
     fn into(self) -> TraceGraphNode<'grammar> {
         TraceGraphNode::Item(self.to_lr0())
     }