Start work on an ARM parser.

pkg/armv4t_asm/README.md

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+<p align="center">
+  <h1 align="center">armv4t_asm</h1>
+  <p align="center">
+    Assembler for the ARMv4T CPU Architecture.
+  </p>
+</p>
+
+_Recommended reading: ["An Introduction to the GNU Assembler"][intro]._
+
+[intro]: doc/gnu_assembler.pdf
+
+## Installation
+
+This package can be used as a standalone executable, or as a dependency.
+
+### CLI
+
+Use [`pub global activate`](https://www.dartlang.org/tools/pub/cmd/pub-global)
+to install the assembler as a local program to be used on the command-line:
+
+```bash
+$ pub global activate armv4t_asm
+$ armv4t_asm filename.s
+> Assembling filename.s as filename.o...
+> Wrote filename.o in 10ms.
+```
+
+Use `armv4t_asm --help` to get full usage information.
+
+### Pub
+
+```yaml
+dependencies:
+  armv4t_asm:
+```
+
+## Usage
+
+TBD.

pkg/armv4t_asm/lib/src/evaluate.dart

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+import 'package:func/func.dart';
+import 'package:math_expressions/math_expressions.dart';
+
+/// Returns the result of evaluating a mathematical [expression].
+dynamic eval(String expression, int lookup(String varName)) => new Parser()
+    .parse(expression)
+    .evaluate(EvaluationType.REAL, new _DynamicContext(lookup));
+
+class _DynamicContext extends ContextModel {
+  final Func1<String, int> _lookup;
+
+  _DynamicContext(this._lookup);
+
+  @override
+  Expression getExpression(String varName) {
+    final result = _lookup(varName);
+    if (result != null) {
+      return new Parser().parse('$result');
+    }
+    return super.getExpression(varName);
+  }
+}