Minor tweaks

rfc.md

@@ -38,8 +38,8 @@ be `0.1.0`.
 
 ## Reusability
 
-In theory, parsing can be a pure function, which takes a `&str` as an
+In theory, the parser can be a pure function, which takes a `&str` as
-input, and produces a `ParseTree` as an output.
+an input, and produces a `ParseTree` as an output.
 
 This is great for reusability: for example, you can compile this
 function to WASM and use it for fast client-side validation of syntax
@@ -64,7 +64,7 @@ Unfortunately, the current libsyntax is far from this ideal. For
 example, even the lexer makes use of the `FileMap` which is
 essentially a global state of the compiler which represents all know
 files. As a data point, it turned out to be easier to move `rustfmt`
-inside of main `rustc` repository than to move libsyntax outside!
+into the main `rustc` repository than to move libsyntax outside!
 
 
 ## IDE support
@@ -86,9 +86,8 @@ necessary to correctly handle certain code-editing actions like
 autoindentation or joining lines. IDE also must be able to produce
 partial parse trees when some input is missing or invalid.
 
-Currently rustc uses the AST approach, which preserves the source code
+Currently rustc uses the AST approach, and preserves some of the
-information to some extent by storing spans in the AST.
+source code information in the form of spans in the AST.
-
 
 
 # Guide-level explanation
@@ -114,8 +113,8 @@ compiler.
 ## Untyped Tree
 
 The main idea is to store the minimal amount of information in the
-tree itself, and instead lean heavily on the source code string for
+tree itself, and instead lean heavily on the source code for the
-the actual data about identifier names, constant values etc.
+actual data about identifier names, constant values etc.
 
 All nodes in the tree are of the same type and store a constant for
 the syntactic category of the element and a range in the source code.
@@ -273,10 +272,12 @@ Note several features of the tree:
 It's hard to work with this raw parse tree, because it is untyped:
 node containing a struct definition has the same API as the node for
 the struct field. But it's possible to add a strongly typed layer on
-top of this raw tree, and get a zero-cost typed AST. Here is an
+top of this raw tree, and get a zero-cost AST. Here is an example
-example which adds type-safe wrappers for structs and fields:
+which adds type-safe wrappers for structs and fields:
 
 ```rust
+// generic infrastructure
+
 pub trait AstNode<'f>: Copy + 'f {
 	fn new(node: Node<'f>) -> Option<Self>;
 	fn node(&self) -> Node<'f>;
@@ -290,6 +291,8 @@ pub fn ast_children<'f, A: AstNode<'f>>(node: Node<'f>) -> Box<Iterator<Item=A>
 	Box::new(node.children().filter_map(A::new))
 }
 
+// AST elements, specific to Rust
+
 #[derive(Clone, Copy)]
 pub struct StructDef<'f>(Node<'f>);
 
@@ -315,22 +318,7 @@ impl<'f> AstNode<'f> for StructDef<'f> {
 	fn node(&self) -> Node<'f> { self.0 }
 }
 
-impl<'f> AstNode<'f> for FieldDef<'f> {
-    fn new(node: Node<'f>) -> Option<Self> {
-        if node.kind() == FIELD_DEF { Some(FieldDef(node)) } else { None }
-    }
-    fn node(&self) -> Node<'f> { self.0 }
-}
-
-impl<'f> AstNode<'f> for TypeRef<'f> {
-    fn new(node: Node<'f>) -> Option<Self> {
-        if node.kind() == TYPE_REF { Some(TypeRef(node)) } else { None }
-    }
-    fn node(&self) -> Node<'f> { self.0 }
-}
-
 impl<'f> NameOwner<'f> for StructDef<'f> {}
-impl<'f> NameOwner<'f> for FieldDef<'f> {}
 
 impl<'f> StructDef<'f> {
 	pub fn fields(&self) -> Box<Iterator<Item=FieldDef<'f>> + 'f> {
@@ -338,11 +326,29 @@ impl<'f> StructDef<'f> {
 	}
 }
 
+
+impl<'f> AstNode<'f> for FieldDef<'f> {
+	fn new(node: Node<'f>) -> Option<Self> {
+		if node.kind() == FIELD_DEF { Some(FieldDef(node)) } else { None }
+	}
+	fn node(&self) -> Node<'f> { self.0 }
+}
+
 impl<'f> FieldDef<'f> {
 	pub fn type_ref(&self) -> Option<TypeRef<'f>> {
 		ast_children(self.node()).next()
 	}
 }
+
+impl<'f> NameOwner<'f> for FieldDef<'f> {}
+
+
+impl<'f> AstNode<'f> for TypeRef<'f> {
+	fn new(node: Node<'f>) -> Option<Self> {
+		if node.kind() == TYPE_REF { Some(TypeRef(node)) } else { None }
+	}
+	fn node(&self) -> Node<'f> { self.0 }
+}
 ```
 
 
@@ -371,9 +377,11 @@ plan is suggested:
 * RFC discussion about the theoretical feasibility of the proposal.
 
 * Implementation of the proposal as a completely separate crates.io
-  crate.
+  crate, by refactoring existing libsyntax source code to produce a
+  new tree.
 
-* A prototype implementation of the macro expansion on top of the new sytnax tree.
+* A prototype implementation of the macro expansion on top of the new
+  sytnax tree.
 
 * Additional round of discussion/RFC about merging with the mainline
   compiler.
@@ -392,6 +400,7 @@ plan is suggested:
 - Incrementally add more information about source code to the current AST.
 - Move the current libsyntax to crates.io as is.
 - Explore alternative representations for the parse tree.
+- Use parser generator instead of hand written parser.
 
 # Unresolved questions
 [unresolved]: #unresolved-questions