Reserve more numeric types

active/0000-reserve-more-numeric-types.md

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+- Start Date: 2014-06-25
+- RFC PR #: (leave this empty)
+- Rust Issue #: (leave this empty)
+
+# Summary
+
+Reserve more numeric types as keywords.
+
+# Motivation
+
+It is conceivable that Rust will gain support for types such as `f128`, `f16`,
+or `u128`. In the interest of backwards compatability, extend the grammar to
+reserve these.
+
+# Detailed design
+
+The `INT_SUFFIX` and `FLOAT_SUFFIX` nonterminals in [the lexical
+grammar](0021-lexical-syntax-simplification.md) respectively become:
+
+```
+INT_SUFFIX : 'i' [0-9]+ ;
+FLOAT_SUFFIX : 'f' [0-9]+ ;
+```
+
+Additionally, identifiers matching those patterns will be *reserved words*,
+not legal for use in bindings or otherwise.
+
+# Drawbacks
+
+Makes the grammar larger for types which we may never use.