diff --git a/c/mapping/mlr_dsl_blocked_ast.c b/c/mapping/mlr_dsl_blocked_ast.c
new file mode 100644
index 000000000..6631ea30a
--- /dev/null
+++ b/c/mapping/mlr_dsl_blocked_ast.c
@@ -0,0 +1,68 @@
+#include "lib/mlr_globals.h"
+#include "lib/mlrutil.h"
+#include "mapping/mlr_dsl_blocked_ast.h"
+
+// ----------------------------------------------------------------
+blocked_ast_t* blocked_ast_alloc(mlr_dsl_ast_t* past) {
+	blocked_ast_t* paast = mlr_malloc_or_die(sizeof(blocked_ast_t));
+
+	paast->pfunc_defs    = sllv_alloc();
+	paast->psubr_defs    = sllv_alloc();
+	paast->pbegin_blocks = sllv_alloc();
+	paast->pmain_block   = mlr_dsl_ast_node_alloc_zary("main_block", MD_AST_NODE_TYPE_STATEMENT_BLOCK);
+	paast->pend_blocks   = sllv_alloc();
+
+	if (past->proot->type != MD_AST_NODE_TYPE_STATEMENT_BLOCK) {
+		fprintf(stderr, "%s: internal coding error detected in file %s at line %d:\n",
+			MLR_GLOBALS.bargv0, __FILE__, __LINE__);
+		fprintf(stderr,
+			"expected root node type %s but found %s.\n",
+			mlr_dsl_ast_node_describe_type(MD_AST_NODE_TYPE_STATEMENT_BLOCK),
+			mlr_dsl_ast_node_describe_type(past->proot->type));
+		exit(1);
+	}
+
+	sllv_t* pnodelist = past->proot->pchildren;
+	while (pnodelist->phead) {
+		mlr_dsl_ast_node_t* pnode = sllv_pop(pnodelist);
+		switch (pnode->type) {
+		case MD_AST_NODE_TYPE_FUNC_DEF:
+			sllv_append(paast->pfunc_defs, pnode);
+			break;
+		case MD_AST_NODE_TYPE_SUBR_DEF:
+			sllv_append(paast->psubr_defs, pnode);
+			break;
+		case MD_AST_NODE_TYPE_BEGIN:
+			sllv_append(paast->pbegin_blocks, pnode);
+			break;
+		case MD_AST_NODE_TYPE_END:
+			sllv_append(paast->pend_blocks, pnode);
+			break;
+		default:
+			sllv_append(paast->pmain_block->pchildren, pnode);
+			break;
+		}
+	}
+
+	return paast;
+}
+
+// ----------------------------------------------------------------
+void blocked_ast_free(blocked_ast_t* paast) {
+	for (sllve_t* pe = paast->pfunc_defs->phead; pe != NULL; pe = pe->pnext)
+		mlr_dsl_ast_node_free(pe->pvvalue);
+	for (sllve_t* pe = paast->psubr_defs->phead; pe != NULL; pe = pe->pnext)
+		mlr_dsl_ast_node_free(pe->pvvalue);
+	for (sllve_t* pe = paast->pbegin_blocks->phead; pe != NULL; pe = pe->pnext)
+		mlr_dsl_ast_node_free(pe->pvvalue);
+	mlr_dsl_ast_node_free(paast->pmain_block);
+	for (sllve_t* pe = paast->pend_blocks->phead; pe != NULL; pe = pe->pnext)
+		mlr_dsl_ast_node_free(pe->pvvalue);
+
+	sllv_free(paast->pfunc_defs);
+	sllv_free(paast->psubr_defs);
+	sllv_free(paast->pbegin_blocks);
+	sllv_free(paast->pend_blocks);
+	free(paast);
+
+}
diff --git a/c/mapping/mlr_dsl_blocked_ast.h b/c/mapping/mlr_dsl_blocked_ast.h
new file mode 100644
index 000000000..59e778a0d
--- /dev/null
+++ b/c/mapping/mlr_dsl_blocked_ast.h
@@ -0,0 +1,25 @@
+#ifndef MLR_DSL_BLOCKED_AST_H
+#define MLR_DSL_BLOCKED_AST_H
+
+#include "containers/mlr_dsl_ast.h"
+#include "containers/sllv.h"
+
+// ================================================================
+// The Lemon parser produces a single raw abstract syntax tree.  This container
+// simply has the subtrees organized by top-level statement blocks. This is just
+// a minor reorganization but it makes stack allocation and CST-builds simpler.
+// ================================================================
+
+typedef struct _blocked_ast_t {
+	sllv_t* pfunc_defs;
+	sllv_t* psubr_defs;
+	sllv_t* pbegin_blocks;
+	mlr_dsl_ast_node_t* pmain_block;
+	sllv_t* pend_blocks;
+} blocked_ast_t;
+
+// This strips nodes off the raw AST and transfers them to the analyzed AST.
+blocked_ast_t* blocked_ast_alloc(mlr_dsl_ast_t* past);
+void blocked_ast_free(blocked_ast_t* paast);
+
+#endif // MLR_DSL_BLOCKED_AST_H