Add enum for user-definable operators.

pkg/front_end/lib/src/fasta/operator.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library fasta.operators;
+
+/// The user-definable operators in Dart.
+///
+/// The names have been chosen to represent their normal semantic meaning.
+enum Operator {
+  Add,

[Lasse Reichstein Nielsen, 2017/02/08 13:15:45]

Using UpperCamelCase is usually reserved for types.

Style guide recommends lowerCamelCase names for constants, allows SCREAMING_CAPS
for backwards compatability. 

[ahe, 2017/02/08 14:03:37]

I've been using CamelCase to avoid conflicts with keywords, for example, see
modifier.dart in this directory.

There are no conflicts here, so I'll change to camelCase.

Since we're discussing this, what are your thoughts on modifier.dart?

+  BitwiseAnd,

[ahe, 2017/02/08 11:49:22]

Note: I'm using "bitwise" prefix here because I think it's clearer when used in
other places in the compiler. This is regardless that, for example, "And", would
be unique in this enum without the prefix.

[Lasse Reichstein Nielsen, 2017/02/08 13:15:46]

Acknowledged.

+  BitwiseNot,
+  BitwiseOr,
+  BitwiseXor,
+  Divide,
+  Equals,
+  GreaterThan,
+  GreaterThanEquals,
+  Index,
+  IndexSet,
+  LeftShift,
+  LessThan,
+  LessThanEquals,
+  Multiply,
+  Percent,

[Lasse Reichstein Nielsen, 2017/02/08 13:15:46]

Should be Modulo

[ahe, 2017/02/08 14:03:37]

Done.

+  RightShift,
+  Subtract,
+  TruncatingDivide,
+  UnaryMinus,
+}
+
+Operator fromString(String string) {
+  if (identical("+", string)) return Operator.Add;
+  if (identical("&", string)) return Operator.BitwiseAnd;
+  if (identical("~", string)) return Operator.BitwiseNot;
+  if (identical("|", string)) return Operator.BitwiseOr;
+  if (identical("^", string)) return Operator.BitwiseXor;
+  if (identical("/", string)) return Operator.Divide;
+  if (identical("==", string)) return Operator.Equals;
+  if (identical(">", string)) return Operator.GreaterThan;
+  if (identical(">=", string)) return Operator.GreaterThanEquals;
+  if (identical("[]", string)) return Operator.Index;
+  if (identical("[]=", string)) return Operator.IndexSet;
+  if (identical("<<", string)) return Operator.LeftShift;
+  if (identical("<", string)) return Operator.LessThan;
+  if (identical("<=", string)) return Operator.LessThanEquals;
+  if (identical("*", string)) return Operator.Multiply;
+  if (identical("%", string)) return Operator.Percent;
+  if (identical(">>", string)) return Operator.RightShift;
+  if (identical("-", string)) return Operator.Subtract;
+  if (identical("~/", string)) return Operator.TruncatingDivide;
+  if (identical("unary-", string)) return Operator.UnaryMinus;

[Lasse Reichstein Nielsen, 2017/02/08 13:15:45]

Would a hash-map possibly be more efficient than linear search?

Probably not a library one, but a custom perfect-hash based one, since you have
a fixed number of known strings. Otherwise the overhead quickly eats doing the
repeated identical tests.

[ahe, 2017/02/08 14:03:37]

I'm concerned about performance here as well. My thoughts have been to add this
information to the corresponding PrecedenceInfo object, see
pkg/front_end/lib/src/fasta/scanner/precedence.dart.

+  return null;
+}