Minor cleanups to custom discriminator code.

Mostly updates to the comments and docs from Pull Request rust-lang#1537.

Author: kevina

doc/tutorial/data.md

@@ -103,9 +103,9 @@ equivalent to a C enum:
 This will define `north`, `east`, `south`, and `west` as constants,
 all of which have type `direction`.
 
-When the enum is is C like, that is none of the variants have
-parameters, it is possible to explicit set the discriminator values to
-an integer value:
+When the enum is C like, that is none of the variants have parameters,
+it is possible to explicitly set the discriminator values to an integer
+value:
 
     enum color {
       red = 0xff0000;

src/comp/middle/ty.rs

@@ -2636,8 +2636,8 @@ fn tag_variants(cx: ctxt, id: ast::def_id) -> @[variant_info] {
         @csearch::get_tag_variants(cx, id)
     } else {
         // FIXME: Now that the variants are run through the type checker (to
-        // check the disr_expr if one exists), this code should likely be
-        // moved there to avoid having to call eval_const_expr twice
+        // check the disr_expr if it exists), this code should likely be
+        // moved there to avoid having to call eval_const_expr twice.
         alt cx.items.get(id.node) {
           ast_map::node_item(@{node: ast::item_tag(variants, _), _}) {
             let disr_val = -1;

src/comp/middle/typeck.rs

@@ -2488,8 +2488,8 @@ fn check_tag_variants(ccx: @crate_ctxt, _sp: span, vs: [ast::variant],
             demand::simple(fcx, e.span, declty, cty);
             // FIXME: issue #1417
             // Also, check_expr (from check_const pass) doesn't guarantee that
-            // the expression in an form that eval_const_expr, so we may still
-            // get an internal compiler error
+            // the expression in an form that eval_const_expr can handle, so
+            // we may still get an internal compiler error.
             alt syntax::ast_util::eval_const_expr(e) {
               syntax::ast_util::const_int(val) {
                 disr_val = val as int;

src/test/run-pass/enum-disr-val-pretty.rs

@@ -9,7 +9,7 @@ fn main() {
     test_color(imaginary, -1, "imaginary");
 }
 
-fn test_color(color: color, val: int, name: str) unsafe{
+fn test_color(color: color, val: int, name: str) {
     assert (color as int == val);
     assert (color as float == val as float);
 }