Generalized lookahead

src/parser/event_parser/grammar/attributes.rs

@@ -9,16 +9,15 @@ pub(super) fn outer_attributes(_: &mut Parser) {
 
 
 fn attribute(p: &mut Parser, inner: bool) -> bool {
-    let attr_start = inner && p.lookahead(&[POUND, EXCL, L_BRACK])
-        || !inner && p.lookahead(&[POUND, L_BRACK]);
-    if !attr_start {
-        return false;
-    }
-    node(p, ATTR, |p| {
-        p.bump_n(if inner { 3 } else { 2 });
+    fn attr_tail(p: &mut Parser) {
         meta_item(p) && p.expect(R_BRACK);
-    });
-    true
+    }
+
+    if inner {
+        node_if(p, [POUND, EXCL, L_BRACK], ATTR, attr_tail)
+    } else {
+        node_if(p, [POUND, L_BRACK], ATTR, attr_tail)
+    }
 }
 
 fn meta_item(p: &mut Parser) -> bool {

src/parser/event_parser/grammar/expressions.rs

@@ -1,16 +1,11 @@
 use super::*;
 
 pub(super) fn literal(p: &mut Parser) -> bool {
-    match p.current() {
-        TRUE_KW | FALSE_KW
-        | INT_NUMBER | FLOAT_NUMBER
-        | BYTE | CHAR
-        |STRING | RAW_STRING | BYTE_STRING | RAW_BYTE_STRING => {
-            node(p, LITERAL, |p| {
-                p.bump();
-            });
-            true
-        }
-        _ => false
-    }
+    let literals = [
+        TRUE_KW, FALSE_KW,
+        INT_NUMBER, FLOAT_NUMBER,
+        BYTE, CHAR,
+        STRING, RAW_STRING, BYTE_STRING, RAW_BYTE_STRING,
+    ];
+    node_if(p, AnyOf(&literals), LITERAL, |_| ())
 }

src/parser/event_parser/grammar/items.rs

@@ -58,7 +58,7 @@ fn struct_field(p: &mut Parser) -> bool {
 
 fn fn_item(p: &mut Parser) {
     p.expect(IDENT) && p.expect(L_PAREN) && p.expect(R_PAREN)
-        && p.curly_block(|p| ());
+        && p.curly_block(|_| ());
 }
 
 

src/parser/event_parser/grammar/mod.rs

@@ -18,13 +18,13 @@ pub(crate) fn file(p: &mut Parser) {
 fn visibility(_: &mut Parser) {
 }
 
-fn node_if<F: FnOnce(&mut Parser)>(
+fn node_if<F: FnOnce(&mut Parser), L: Lookahead>(
     p: &mut Parser,
-    first: SyntaxKind,
+    first: L,
     node_kind: SyntaxKind,
     rest: F
 ) -> bool {
-    p.current() == first && { node(p, node_kind, |p| { p.bump(); rest(p); }); true }
+    first.is_ahead(p) && { node(p, node_kind, |p| { L::consume(p); rest(p); }); true }
 }
 
 fn node<F: FnOnce(&mut Parser)>(p: &mut Parser, node_kind: SyntaxKind, rest: F) {
@@ -99,13 +99,63 @@ impl<'p> Parser<'p> {
         }
     }
 
-    fn bump_n(&mut self, n: u8) {
-        for _ in 0..n {
-            self.bump();
-        }
-    }
-
     fn eat(&mut self, kind: SyntaxKind) -> bool {
         self.current() == kind && { self.bump(); true }
     }
+}
+
+trait Lookahead: Copy {
+    fn is_ahead(self, p: &Parser) -> bool;
+    fn consume(p: &mut Parser);
+}
+
+impl Lookahead for SyntaxKind {
+    fn is_ahead(self, p: &Parser) -> bool {
+        p.current() == self
+    }
+
+    fn consume(p: &mut Parser) {
+        p.bump();
+    }
+}
+
+impl Lookahead for [SyntaxKind; 2] {
+    fn is_ahead(self, p: &Parser) -> bool {
+        p.current() == self[0]
+        && p.raw_lookahead(1) == self[1]
+    }
+
+    fn consume(p: &mut Parser) {
+        p.bump();
+        p.bump();
+    }
+}
+
+impl Lookahead for [SyntaxKind; 3] {
+    fn is_ahead(self, p: &Parser) -> bool {
+        p.current() == self[0]
+        && p.raw_lookahead(1) == self[1]
+        && p.raw_lookahead(2) == self[2]
+    }
+
+    fn consume(p: &mut Parser) {
+        p.bump();
+        p.bump();
+        p.bump();
+    }
+}
+
+#[derive(Clone, Copy)]
+struct AnyOf<'a>(&'a [SyntaxKind]);
+
+impl<'a> Lookahead for AnyOf<'a> {
+    fn is_ahead(self, p: &Parser) -> bool {
+        let curr = p.current();
+        self.0.iter().any(|&k| k == curr)
+    }
+
+    fn consume(p: &mut Parser) {
+        p.bump();
+    }
+
 }

src/parser/event_parser/parser.rs

@@ -88,12 +88,8 @@ impl<'t> Parser<'t> {
         kind
     }
 
-    pub(crate) fn lookahead(&self, kinds: &[SyntaxKind]) -> bool {
-        if self.tokens[self.pos..].len() < kinds.len() {
-            return false
-        }
-        kinds.iter().zip(self.tokens[self.pos..].iter().map(|t| t.kind))
-            .all(|(&k1, k2)| k1 == k2)
+    pub(crate) fn raw_lookahead(&self, n: usize) -> SyntaxKind {
+        self.tokens.get(self.pos + n).map(|t| t.kind).unwrap_or(EOF)
     }
 
     pub(crate) fn curly_block<F: FnOnce(&mut Parser)>(&mut self, f: F) -> bool {

src/parser/mod.rs

@@ -56,4 +56,4 @@ fn is_insignificant(kind: SyntaxKind) -> bool {
         WHITESPACE | COMMENT => true,
         _ => false,
     }
-}
+}