Resources for Amateur Compiler Writers
c9x.me
c9x.me
On the other hand, I would love to see "HTML5 and CSS parsing and rendering for amateurs". Given the state of modern HTML5 and CSS standards, and ignoring compatibility and real-world usage (just like for toy compilers), Let's Build A Browser Engine sounds more tempting than Let's Build a Compiler.
(To preempt "contribute to existing actual real-world engine" suggestions -- while that's worthwhile, it's like saying "contribute to LLVM" to someone looking to write a toy compiler, ie. completely misses the point).
FWIW, current HTML and CSS standards should give you compatibility with real-world usage if you implement them accurately. Of course, for a toy, you may well want to simplify things from what the standard does.
Re HTML5/CSS
Excellent idea! These slways need more work in some way plus have widedpread impact. Amateurs stumbling on improved algorithms might similarly see their work have great impact.
The high-level abstractions of HTML/CSS are really powerful, but it would be cool to have an understanding of the implications of such designs when writing web applications.
As an amateur compiler writer you would probably want to make something useful in a few weeks, not waste a year playing around. And it's a very different story. It's essentially about making a meta DSL, that compiles into another language and plays well with existing libraries, tooling, the whole ecosystem, but also does something special and useful for you. So, you should learn parsing, possibly recursive descend for the code and something else for expressions, a bit about working with ASTs and that's pretty much it.
I am in it for the money which I guess makes me a pro but I don't have a computer science background and frankly in 2016 I am afraid the average undergrad compiler course is part of the problem as much as the solution.
Another big issue is nontraditional compilers of many kinds such as js accelerators and things that compile to JavaScript, domain specific languages, data flow systems, etc. Frankly I want to generate Java source or JVM byte code and could care less for real machine code.
What do you mean by that?
Instead, I figure a course should cover basics of DSL design, types and type inference, working with ASTs, some static analysis and a few other things. That has some overlap with a traditional compilers course, but a pretty different focus.
You don't really need more than a typechecker and ast tranformations for that.
This is a more advanced tutorial that illustrates a nice but tricky optimization that OCaml's type checker internally uses: http://okmij.org/ftp/ML/generalization.html
Finally, TAPL's type checkers are pretty good. They aren't designed for efficiency, though. They're designed to closely follow the book's contents: http://www.cis.upenn.edu/~bcpierce/tapl/checkers/
[1]: https://github.com/dotnet/roslyn/tree/master/src/Compilers/C...
I'm trying to write a compiler for LISP - i wrote a simple interpreter already (mostly just to learn how compilers work). Definitely did not need anything complicated for tokenizing,parsing thanks to https://github.com/lihaoyi/fastparse.
What resources are useful now for learning about implementing a type system and the optimizer? You said register coloring etc. arent important - is this because we can target LLVM?
What would a modern parser use instead?
Or is it just that for most compiler work the parser has already been written?
I've also really enjoyed Elements of Programming Languages by Friedman & Wand (older editions cover different topics than the current 3rd edition, and it may be worth reading both the 1st and 3rd editions). Focuses primarily on interpreters, but most of the topics covered have applications for compilers as well.
Going a slightly more traditional route, I've found Andrew Appel's compiler books, Modern Compiler Implementation in ML and Compiling with Continuations to present pretty wide coverage of techniques at all phases of a compiler. The former is the one I normally recommend for people looking for their first (and hopefully only) compiler book (if they're actually looking for a compiler book rather than a DSL book).
Of course, techniques for processing the Lisp family are well-covered in Christian Quiennec's classic Lisp in Small Pieces (he's written some other books which are quite interesting for Lisp historians as well). Implementors of Lisps will also probably want to look into The Art of the Metaobject Protocol by Kiczales et al. SICP's coverage in chapters 4 and 5 is also pretty good as an introduction, even if it only barely scratches the surface.
Getting into types, you're pretty much limited to Pierce's Types and Programming Languages, but Bob Harper et al. have also written Homotopy Type Theory which is freely available on the Web. I haven't finished HoTT yet, so I can't comment on how accessible it is or how broad/deep its coverage is.
Those interested in rewriting systems should start with Term Rewriting and All That by Baader and Nipkow, which I've found to be extremely accessible and fairly comprehensive (covering abstract rewriting systems, string rewriting, graph rewriting, etc.). Your choices for books on rewriting written in English is pretty small (I've literally found only three, one of which costs $300 USD(!) -- where does Cambridge University Press get off??), but fortunately the Baader and Nipkow book is so good that you probably won't need another book and can proceed straight to the literature.
---
There are tons of books on compilation, but I honestly think they're mostly a waste of time. Each book, for the most part, only re-iterates the basics in another way, so unless you didn't quite grasp it from the first book you tried, maybe look at another one, but once you understand the material, don't waste any more time or money on compiler books. After you've grokked the basics (i.e., worked through one or two introductory books), you'll get far more value from reading books on other related concepts (e.g., type theory, term rewriting, metaobject protocols, etc.), reading research papers, journal articles, dissertations, etc., and, of course, reading code.
I say all this as someone who made the mistake of spending lots of time and money on lots of different compiler books, stupidly hoping to learn something new with each one. The silver lining is that this puts me in a pretty good position to recommend particular compiler books :)
That the Dragon Book is still considered the standard introduction is baffling, even the most recent edition is horrendously outdated and dwells far too much on parsing techniques (where, from the perspective of a compiler writer, parsing is effectively a solved problem -- not to mention that there are quite a few parsing techniques the Dragon Book doesn't cover, despite the amount of text devoted to parsing). And, like you said, the techniques it covers are really only immediately applicable to imperative procedural languages without sophisticated type systems, such as C or Pascal.
There's nothing exciting about coding up a toy version of "Pascal" but it would be exciting if you could add the "unless" construction from Perl to Java in <1000 lines of code.
We are just now coming out of a dark ages in compilers that was brought on by gcc.
Before gcc you could make a living writing compilers (i.e. Turbo C, Turbo Pascal, Turbo Prolog, ...) at a moderately sized company. Today you have gcc and you have compilers from the likes of Intel and Microsoft.
LLVM breathed some life into gcc since it is now modularized so that you can do interesting things on top of gcc.
* The language you are using to write the compiler. You have to know it well enough to write a complex application.
* The language you are compiling. You have to completely understand it.
* The language you are compiling to: x86, JVM, etc. You have to understand it well enough to write every complex application.
Unless you are writing an optimizing compiler, you just have to understand the target language well enough to write snippets that resemble the operations of your source or intermediate language, which can be pretty little. See:
http://t3x.org/subc/cg386.c.html
Anecdotally: I have once written an AXP21164 back-end without any prior knowledge, only based on the reference manual. It was not pretty or fast, but it worked.
If you are compiling for x86 you have to think about register allocation.
If you are compiling for JVM or an HLL, you don't. A good chunk of what is discussed in that article just is not relevant anymore.
Also, if you aren't writing a register allocator because you're using the JVM or LLVM, then someone else needs to on your behalf. We can't forget these skills.
Normally the cost isn't too bad and of course they're spilled to the stack not kept in registers, but if the language you are implementing has thousands of locals you may even reach the limit of the frame size. We've seen this in practice in more than one language and application.
Also, only some frames are JIT compiled - what about the rest?
But if you're really running into the 64k limit on max_locals even with index reuse, then you're out of luck.
For every local variable index, the JVM needs to keep the value live for the duration of the method because that's what the debugger will show.
And yes we have seen the 64k limit blown by real programs in the wild that aren't designed to be awkward (I'm in the VM research group at Oracle).
Inventing whatever semantics you have in mind without considering how it's going to be compiled is a recipe for slow languages.
If you are mostly interested in principles rather than the most recent tooling, there's a course by Wirth that makes it tractable.
More here: http://short-sharp.blogspot.ca/2014/08/building-compiler-bri...
Also, after reading What every compiler writer should know about programmers, I finally understand why people hate C. Because this just shows definitively that C compiler writers have been in their own little world for the past few decades.
Man, now I want a C compiler that wasn't written by a bunch of mindless jerks that will be the first up against the wall when the revolution comes...
If I tell you that a function may call any function, then you already know everything you need to know for recursion. If we didn't have recursion, only then would I need to qualify what I just told you with the restriction that a function can only be active once.
When I show students recursion I can't understand their confusion. I think to myself 'but I already showed you functions can call any other function, why do you see this case differently?'
(Obviously I try to be more patient, understanding and anticipatory in person.)
Most programming I learned was imperative. As I wrote the code, I imagined the execution in my head. This led to a problem where when I was halfway through a function, and it referred to itself, my brain would segfault. How could something I was not yet done writing refer to itself? I hadn't finished yet, so my brain could not comprehend what such a reference would mean.
It was also difficult because I wanted to think of functions as nice neat pieces of code that would take some data, do it's thing, and return a value. I could mentally inline a function call without much effort.
But when recursion is introduced, the floor drops out of my mental inlining. Suddenly my mental effort for such things becomes huge. For me anyway. My brain doesn't like to float around in abstraction land for long, it needs to periodically be anchored in the concrete. Otherwise I quickly lose my sense of direction and orientation... I lose my context.
Declarative languages actually make these easier, for me, because I'm not mentally executing a recipe as I write. I am giving a piece-wise description of what something is. So there is no mental tracing.
I expect the a-ha moment for recursion is different for everyone. But just showing recursion in many different forms would probably help. For example, show fib sequence generation where instead of the function calling itself, each function calls a uniquely named function... such that you concretely demonstrate building the first 5 or so numbers in the sequence...
Then show the similarity of the functions, show what the computer has to keep track of with the nested function calls, and step by step work your way to straight recursion.
Show it in BASIC with GOTO statements.
Finding as many different ways to concretely demonstrate an abstract concept will help reach more people.
1. I do still inline recursive functions, but I've learned to selectively inline just the base case when I first implement recursion. Paradoxically, experience with lisp helped me with recursion in C, particularly Common Lisp's trace facility which taught me to visualize stacks of multiple function calls (whether recursive or not) rather than a single one at a time.
2. I've learned to think declaratively even when I program in C. When writing a C function I might start out with a crisp definition in my head ("this function saves the reverse of the list seen so far in its second argument") so that I can rely on that definition even when the implementation isn't yet complete.
[1] http://akkartik.name/post/mu
[2] https://news.ycombinator.com/favorites?id=akkartik&comments=...
That should happen naturally, if you implement a compiler to native code. A "call" instruction is just a "goto/branch/jump" with some extra stack fiddling.
Also, I don't think pure functions are so easy mentally either. Try to understand "call with current continuation". ;)
Recursion is likely to expose bugs in the calling convention if you're writing your first compiler.
If I give you a list of requirements for a programming language that I want you to implement and it includes 'a function must be able to call any function' then you have recursion. You don't need additional separate requirement for 'and that function may be itself', as long as you've fully implemented the first requirement. In fact you'd need an extra requirement to prevent recursion, not to allow it.
That's what I mean by you shouldn't need to consider recursion as a special case.
The fact it is not an additional requirement to allow recursion is irrealevent, what matter is that its extra complexity to handle that case correctly.
Not that I think that is the OP's problem - just a bit of interesting history. Support for recursion may seem obvious in hindsight, but there was a time where that wasn't the case.
Also, just to be clear, I understand how recursion works as a user of a programming language, though implementing it is different than using it.
Assume the following AST.
FN_DEF: { NAME: foo, PARAMS: [int4 param1, int4 param2] }
LOCAL_VARS: [int4 var1, int4 var2, int4 var3]
...
ASSIGN: { var1, CONST: 0x1 }
ASSIGN: { var2, ADD:{ 0x2, param1 } }
...
var3 = FN_CALL: { foo, ARGS: [var1, var2] }
...
RETURN: { var3 }
fn_foo:
push ebp ; save the caller's old frame pointer
mov ebp, esp ; the new frame pointer to current stack ptr
sub esp, 20 ; make new space in stack for params and locals
; EBP points to the base of the current frame
; the frame has 20 bytes in the stack
; var1 at [ebp-4]
; var2 at [ebp-8]
; var3 at [ebp-12]
; param1 at [ebp-16]
; param2 at [ebp-20]
...
mov [ebp-4], 1 ; assign 0x1 to var1
mov [ebp-8], 2 ; assign 0x2 to var2
add [ebp-8], [ebp-16] ; add param1 to var2
...
push [ebp-4] ; push var1 for the function call
push [ebp-8] ; push var2 for the function call
call fn_foo ; call function foo at address fn_foo
; the current EIP is saved in stack
; the return value will be in EAX
mov [ebp-12], eax ; save function return value to var3
...
mov eax, [ebp-12] ; set function return value from var3
mov esp, ebp ; pop frame
pop ebp ; restore old EBP to previous frame
ret ; return to the caller by popping the
; caller's address from stack into EIP.
; Execution will continue at the restored EIP address.It doesn't allow you to support syntactic mutual recursion but it's easy to do and can be implemented without data modification at any level.
There shouldn't be any need for recursive calls to be a special kind of call. They caller shouldn't need to know that it is calling itself (again, lack of special casing).
This is how recursion works in languages like Java, Python, Ruby, C.
In my language, there is no special global scope for variables; every program is basically one giant (extended and sugared) lambda calculus expression.
I do use lambda-lifting so that in the C code I generate, there is a C function in the global C namespace that is called to execute an object-language function but object-language functions also have closure environments so any kind of self-reference needs to include both the global C function and the closure environment for that particular closure.
Note that my language does support modularity (breaking programs into multiple files, basically). However, the mechanism for referring to "packages" (stuff in other files) uses a separate name system.
I agree that languages that bind all functions in a global scope can easily use that global scope to resolve recursive references. It's also easier when your language supports variable assignment and destructive updates of data structures. But my language doesn't support those things either. :)
Addendum: By the way, you mentioned Java, Python, and Ruby, which are all object-oriented. Of course, the recursion among methods in those languages arises in a way that's very similar to passing a callee as a hidden argument. In OO languages, the hidden argument is "self" or "this"!
A scope environment gives you a place to name "things". "Things" can be functions. It's just a name-value map. You create a local scope environment for every function invocation. You can bind things (value or functions) to names in the local environment. Then you can refer to "things" by their names, like calling a function using its name.
Parent scope environments can be nested in the local scope when the function is called. A search on a name not found on the current scope can be delegated to the parent scope, so that functions defined and named in outer scope can be referenced in inner scope.
Recursive call is not a problem for named function since you can look up the function by name. It becomes a problem for anonymous function (lambda) since it can't be looked by name. For that you can introduce a special name like "_lamb" for it. Upon entry of a function, you bind the current function to the name in the current environment. A reference to it would call the current function again. e.g. _lamb(). You can even have a special name "_parent" to bind to the parent environment. In that case you can call the anonymous parent function. E.g. _parent._lamb()
Function calling and recursive function have nothing to do with OO or Java/Python/Ruby. It has everything to do with name, binding, scope, and environment.
Self or this allows you to refer to the same object. You don't need to refer to the same object to wind up calling the same method. You could have two different objects that just have the same method. Maybe they share a class, or a mixin, or whatever. So I'm not sure self is relevant here.
I don't mean to disagree with the point you are making! It's a valid point.
However, I would like to emphasize that some languages have syntactic properties that complicate things a bit and I feel that a comment about how things "should" be really ought to be qualified by something like, "in a mainstream Java-like language".
Consider the simply-typed lambda calculus, or Martin-Löf type theory. These languages don't allow general recursion but it's not because they are always poorly implemented!
The only situation where recursion wouldn't work is where all of your vars are static.
As for compiling Lexical scoping, I can't help you there, although I've heard it's not too hard, if you don't care about optimization. Dynamic scoping is dead simple to compile, though.
As for tail call optimization, if your target is an assembler with a goto instruction that in any way resembles a real instruction set, the only slightly tricky bit is figuring out what function is in the tail position. Once you've done that, it shouldn't be too hard. Lambda, The Ultimate Declaritive has details, IIRC.
Anyway, it's very readable.
Once the parser returns the AST, it is getting more complicated, how to decorate an AST, add actions, etc. still looking to learn more about compiler backends
http://matt.might.net/articles/books-papers-materials-for-gr...