Fabrice Ferreira Leal fabriceleal

This document explains how I would implement an SSA-based compiler if I was writing one today.

This document is intentionally opinionated. It just tells you how I would do it. This document is intended for anyone who has read about SSA and understands the concept, but is confused about how exactly to put it into practice. If you're that person, then I'm here to show you a way to do it that works well for me. If you're looking for a review of other ways to do it, I recommend this post.

My approach works well when implementing the compiler in any language that easily permits cyclic mutable data structures. I know from experience that it'll work great in C++, C#, or Java. The memory management of this approach is simple (and I'll explain it), so you won't have to stress about use after frees.

I like my approach because it leads to an ergonomic API by minimizing the amount of special cases you have to worry about. Most of the compiler is analyses and transformations ov

Reader Macros in Common Lisp

This post also appears on lisper.in.

Reader macros are perhaps not as famous as ordinary macros. While macros are a great way to create your own DSL, reader macros provide even greater flexibility by allowing you to create entirely new syntax on top of Lisp.

Paul Graham explains them very well in [On Lisp][] (Chapter 17, Read-Macros):

The three big moments in a Lisp expression's life are read-time, compile-time, and runtime. Functions are in control at runtime. Macros give us a chance to perform transformations on programs at compile-time. ...read-macros... do their work at read-time.

	type term =
	\| Lam of (term -> term)
	\| Pi of term * (term -> term)
	\| Appl of term * term
	\| Ann of term * term
	\| FreeVar of int
	\| Star
	\| Box

	let unfurl lvl f = f (FreeVar lvl)

	(* The syntax of our calculus. Notice that types are represented in the same way
	as terms, which is the essence of CoC. *)
	type term =
	\| Var of string
	\| Appl of term * term
	\| Binder of binder * string * term * term
	\| Star
	\| Box

	and binder = Lam \| Pi

	# From:
	# http://stackoverflow.com/questions/17475587/setup-mod-proxy-on-apache-http-server
	# http://www.forums.serverwatch.com/showthread.php?16887-mod_proxy-problem
	# http://serverfault.com/questions/242650/setting-up-a-basic-mod-proxy-virtual-host
	# http://stackoverflow.com/questions/14775248/apache-http-proxy-based-on-hostname
	# http://stackoverflow.com/questions/1997001/setting-up-a-basic-web-proxy-in-apache
	# http://ubuntuforums.org/showthread.php?t=983222
	#

	# put on httpdvhosts.conf

	( ** Exercise: 2 stars (andb_eq_orb) *)
	(** Prove the following theorem. (You may want to first prove a
	subsidiary lemma or two.) *)

	Lemma orb_always_true :
	forall b,
	orb true b = true.
	Proof. reflexivity. Qed.

	Lemma andb_always_false :

	' http://support.microsoft.com/kb/291296/en-us
	' http://superuser.com/questions/130592/how-do-you-force-excel-to-quote-all-columns-of-a-csv-file
	' - change integer to long indexing
	' http://stackoverflow.com/questions/2524703/save-text-file-utf-8-encoded-with-vba
	' - output utf8 content

	Sub QuoteCommaExport()
	' Dimension all variables.
	Dim DestFile As String
	Dim FileNum As Integer


	gcc -E -P some.h > some.prep.h