1 * MCS: The Ximian C# compiler
3 MCS began as an experiment to learn the features of C# by
4 writing a large C# program. MCS is currently able to parse C#
5 programs and create an internal tree representation of the
6 program. MCS can parse itself.
8 Work is progressing quickly on various fronts in the C#
9 compiler. Recently I started using the System.Reflection API
10 to load system type definitions and avoid self-population of
11 types in the compiler and dropped my internal Type
12 representation in favor of using the CLI's System.Type.
14 ** Phases of the compiler
16 The compiler has a number of phases:
19 * Lexical analyzer: hand-coded lexical analyzer that
20 provides tokens to the parser.
22 * The Parser: the parser is implemented using Jay (A
23 Berkeley Yacc port to Java, that I ported to C#).
24 The parser does minimal work and syntax checking,
25 and only constructs a parsed tree.
27 Each language element gets its own class. The code
28 convention is to use an uppercase name for the
29 language element. So a C# class and its associated
30 information is kept in a "Class" class, a "struct"
31 in a "Struct" class and so on. Statements derive
32 from the "Statement" class, and Expressions from the
35 * Parent class resolution: before the actual code
36 generation, we need to resolve the parents and
37 interfaces for interface, classe and struct
40 * Semantic analysis: since C# can not resolve in a
41 top-down pass what identifiers actually mean, we
42 have to postpone this decision until the above steps
45 * Code generation: nothing done so far, but I do not
46 expect this to be hard, as I will just use
47 System.Reflection.Emit to generate the code.
52 ** Current pending tasks
57 * Array declarations are currently being ignored,
59 * PInvoke declarations are not supported.
61 * Pre-processing is not supported.
63 * Attribute declarations and passing currently ignored.
65 * Compiler does not pass around line/col information from tokenizer for error reporting.
67 * Jay does not work correctly with `error'
68 productions, making parser errors hard to point. It
69 would be best to port the Bison-To-Java compiler to
70 become Bison-to-C# compiler (bjepson@oreilly.com
71 might have more information)
77 * Resolve "base" classes and "base" interfaces for
78 classes, structs and interfaces.
80 Once this is done, we can actually do the semantic
81 analysis, because otherwise we do not know who our
85 ** Questions and Answers
87 Q: Why not write a C# front-end for GCC?
89 A: I wanted to learn about C#, and this was an exercise in this
90 task. The resulting compiler is highly object-oriented, which has
91 lead to a very nice, easy to follow and simple implementation of
94 I found that the design of this compiler is very similar to
95 Guavac's implementation.
97 Targeting the CIL/MSIL byte codes would require to re-architecting
98 GCC, as GCC is mostly designed to be used for register machines.
100 The GCC Java engine that generates Java byte codes cheats: it does
101 not use the GCC backend; it has a special backend just for Java, so
102 you can not really generate Java bytecodes from the other languages
105 Q: If your C# compiler is written in C#, how do you plan on getting
106 this working on a non-Microsoft environment.
108 We will do this through an implementation of the CLI Virtual
109 Execution System for Unix (our JIT engine).
113 A: No, currently I am using Jay which is a port of Berkeley Yacc to
114 Java that I later ported to C#. This means that error recovery is
115 not as nice as I would like to, and for some reason error
116 productions are not being caught.
118 In the future I want to port one of the Bison/Java ports to C# for
121 Q: How do I compile it?
123 A: Compiling MCS currently requires you to run my port of <a
124 href="http://primates.ximian.com/~miguel/code/jay.cs.tar.gz">Jay to
125 C#</a> on a Unix system to generate the parser, and then you need
126 to use Microsoft's .NET csc.exe compiler to compile the compiler.
128 You only need to compile the compiler compiler (C code), the
129 samples are Java samples that I did not port, and you do not need
132 It might be simple to port Jay.cs to Windows, but I have not tried
135 You might also want to look at the <a href="faq.html#gcc">GCC</a>
136 section on the main FAQ