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+- A slightly edited irc discussion with Josh Triplett.
+- Describes most data structures used in sparse.
+
+As far as the parsing structures go...
+The C parser exists in two main files: parse.c, which parses statements, and expression.c, which parses expressions.
+parse.h contains the definition of struct statement, which represents a C statement.
+That includes only those things which can't appear as an expression, which primarily includes control flow statements such as if, loops, switch/case, and goto.
+expression.h contains the definition of struct expression, which represents a C expression.  That has a lot more content, since most C constructs can appear in expressions.
+A series of statements forms a compound statement (STMT_COMPOUND).
+That appears as another struct statement which has a statement_list member.
+A function body consists of a compound statement.
+When you look at a loop body, if or else body, or case body, you'll notice that they just have a struct statement, not a statement_list; they can have multiple statements by using a compound statement.
+Also note that all loops get turned into a single "iterator" statement.
+for, while, and do-while.
+A symbol, then, represents a name in a C file.  A symbol might represent a variable, a function, a label, or various other things.
+See symbol.h.
+"struct symbol" represents one symbol.
+As with the various other structures, it has some common data and a union of sub-structures for the parts that differ between different types.
+Most of the interesting bits come in the NS_SYMBOL case.
+Among other things, it has a struct statement for the body of a function (if any), a list of symbols for the arguments, an expression for a variable initializer, and so on.
+Together, struct symbol, struct statement, and struct expression represent most of the abstract syntax tree for C.
+So, that represents most of the "front-end" of Sparse: parsing C and generating that abstract syntax tree.
+That much occurs in pretty much any program using the Sparse frontend.
+The backend varies among programs.
+For instance, the c2xml backend goes that far, then outputs XML.
+The sparse static analysis backend has a few steps: it generates linearized bytecode, does some evaluation on that, and outputs some warnings.
+Several other backends run that linearized bytecode stage.
+The linearized bytecode itself has a set of nested structures.
+linearize.h defines all of them.
+At the top level, it has struct entrypoint.
+That represents an entrypoint to the code, which would normally mean a function.
+An entrypoint has a list of basic blocks.
+struct basic_block.
+A basic block represents a series of instructions with no branches.
+Straight-line code.
+A branch only occurs at the end of a basic block, and branches can only target the beginning of a basic block.
+Typically, a conditional will consist of a basic block leading up to the branch, a basic block for the true case, a basic block for the false case, and a basic block where the two paths merge back together.
+Either the true or the false case may not exist.
+A loop will normally have a basic block for the loop body, which can branch to the top at the end or continue to the next basic block.
+So basic blocks represent a node in the control flow graph.
+The edges in that graph lead from one basic block to a basic block which can follow it in the execution of the program.
+Each basic block has a series of instructions, "struct instruction".
+"enum opcode" lists all the instructions.
+Fairly high-level instruction set, corresponding directly to bits of C.
+So you have an entrypoint, which has a graph of basic blocks, each of which has a list of instructions.
+An entrypoint also has a pointer to the first instruction.
+One last bit of trickiness: struct pseudo.
+Have you ever heard of "static single assignment" or SSA form?
+struct pseudo represents one of those single-assignment variables.
+Each one has a pointer to the symbol it represents (which may have many pseudos referencing it).
+Each one also has a pointer to the instruction that defines it.
+That covers most of the major data structures in Sparse.
+Now, given all that, some of the top-level stuff in sparse.c may make more sense.
+For instance, the context checking works in terms of basic blocks.
+Hopefully some of that helped you understand Sparse better.
