Added regex backend, does not compile

src/backends/regex.h

@@ -0,0 +1,38 @@
+// Internal defs
+#ifndef HAMMER_BACKEND_REGEX__H
+#define HAMMER_BACKEND_REGEX__H
+
+// each insn is an 8-bit opcode and a 16-bit parameter
+// [a] are actions; they add an instruction to the stackvm that is being output.
+// [m] are match ops; they can either succeed or fail, depending on the current character
+// [c] are control ops. They affect the pc non-linearly.
+typedef enum HRVMOp_ {
+  RVM_ACCEPT,  // [a]
+  RVM_GOTO,    // [c] parameter is an offset into the instruction table
+  RVM_FORK,    // [c] parameter is an offset into the instruction table
+  RVM_PUSH,    // [a] No arguments, just pushes a mark onto the stack
+  RVM_ACTION,  // [a] argument is an action ID
+  RVM_CAPTURE, // [a] Capture the last string, and push it on the stack. No arg.
+  RVM_EOF,     // [m] Succeeds only if at EOF.
+  RVM_MATCH,   // [m] The high byte of the parameter is an upper bound
+	       //     and the low byte is a lower bound, both
+	       //     inclusive. An inverted match should be handled
+	       //     as two ranges.
+  RVM_STEP,    // [a] Step to the next byte of input
+  RVM_OPCOUNT
+} HRVMOp;
+
+typedef struct HRVMInsn_{
+  uint8_t op;
+  uint16_t arg;
+} HRVMInsn;
+
+
+typedef struct HRVMProg_ {
+  size_t length;
+  size_t action_count;
+  HAction *actions;
+  HRVMInsn *insns;
+};
+
+#endif