diff --git a/c/containers/join_bucket_keeper.c b/c/containers/join_bucket_keeper.c
index 86d4f00bc..3a17c9553 100644
--- a/c/containers/join_bucket_keeper.c
+++ b/c/containers/join_bucket_keeper.c
@@ -192,14 +192,14 @@ join_bucket_keeper_t* join_bucket_keeper_alloc_from_reader(
 }
 
 // ----------------------------------------------------------------
-void join_bucket_keeper_free(join_bucket_keeper_t* pkeeper) {
+void join_bucket_keeper_free(join_bucket_keeper_t* pkeeper, char* prepipe) {
 	if (pkeeper == NULL)
 		return;
 	if (pkeeper->pbucket->pleft_field_values != NULL)
 		slls_free(pkeeper->pbucket->pleft_field_values);
 	if (pkeeper->pbucket->precords != NULL)
 		sllv_free(pkeeper->pbucket->precords);
-	pkeeper->plrec_reader->pclose_func(pkeeper->plrec_reader->pvstate, pkeeper->pvhandle);
+	pkeeper->plrec_reader->pclose_func(pkeeper->plrec_reader->pvstate, pkeeper->pvhandle, prepipe);
 	free(pkeeper);
 }
 
diff --git a/c/containers/join_bucket_keeper.h b/c/containers/join_bucket_keeper.h
index e1e3d7394..e3c7e6a6d 100644
--- a/c/containers/join_bucket_keeper.h
+++ b/c/containers/join_bucket_keeper.h
@@ -53,7 +53,7 @@ join_bucket_keeper_t* join_bucket_keeper_alloc_from_reader(
 	char*          left_file_name,
 	slls_t*        pleft_field_names);
 
-void join_bucket_keeper_free(join_bucket_keeper_t* pkeeper);
+void join_bucket_keeper_free(join_bucket_keeper_t* pkeeper, char* prepipe);
 
 // *pprecords_paired should not be freed by the caller.
 // *pprecords_left_unpaired should be freed by the caller.
diff --git a/c/experimental/getlines.c b/c/experimental/getlines.c
index 379acebba..dcbb8fa46 100644
--- a/c/experimental/getlines.c
+++ b/c/experimental/getlines.c
@@ -317,7 +317,7 @@ static int read_file_mmap_psb(char* filename, int do_write) {
 		bc += strlen(line);
 	}
 	sb_free(psb);
-	file_reader_mmap_close(ph);
+	file_reader_mmap_close(ph, NULL);
 	return bc;
 }
 
diff --git a/c/input/byte_reader.h b/c/input/byte_reader.h
index 17032c54d..26644e0c7 100644
--- a/c/input/byte_reader.h
+++ b/c/input/byte_reader.h
@@ -18,7 +18,7 @@ typedef int   byte_reader_read_func_t(struct _byte_reader_t* pbr);
 
 // The close function should close file pointers/descriptors, as well as any
 // necessary heap-frees.
-typedef void  byte_reader_close_func_t(struct _byte_reader_t* pbr);
+typedef void  byte_reader_close_func_t(struct _byte_reader_t* pbr, char* prepipe);
 
 typedef struct _byte_reader_t {
 	void*                       pvstate;
diff --git a/c/input/file_reader_mmap.c b/c/input/file_reader_mmap.c
index 12f21c797..3946e26f3 100644
--- a/c/input/file_reader_mmap.c
+++ b/c/input/file_reader_mmap.c
@@ -43,7 +43,7 @@ file_reader_mmap_state_t* file_reader_mmap_open(char* prepipe, char* file_name)
 }
 
 // ----------------------------------------------------------------
-void file_reader_mmap_close(file_reader_mmap_state_t* pstate) {
+void file_reader_mmap_close(file_reader_mmap_state_t* pstate, char* prepipe) {
 	if (close(pstate->fd) < 0) {
 		perror("close");
 		exit(1);
@@ -57,6 +57,6 @@ void* file_reader_mmap_vopen(void* pvstate, char* prepipe, char* file_name) {
 }
 
 // ----------------------------------------------------------------
-void file_reader_mmap_vclose(void* pvstate, void* pvhandle) {
-	file_reader_mmap_close(pvhandle);
+void file_reader_mmap_vclose(void* pvstate, void* pvhandle, char* prepipe) {
+	file_reader_mmap_close(pvhandle, prepipe);
 }
diff --git a/c/input/file_reader_mmap.h b/c/input/file_reader_mmap.h
index 3186ed1c0..08e09ff03 100644
--- a/c/input/file_reader_mmap.h
+++ b/c/input/file_reader_mmap.h
@@ -12,9 +12,9 @@ typedef struct _file_reader_mmap_state_t {
 } file_reader_mmap_state_t;
 
 file_reader_mmap_state_t* file_reader_mmap_open(char* prepipe, char* file_name);
-void file_reader_mmap_close(file_reader_mmap_state_t* pstate);
+void file_reader_mmap_close(file_reader_mmap_state_t* pstate, char* prepipe);
 
 void* file_reader_mmap_vopen(void* pvstate, char* prepipe, char* file_name);
-void file_reader_mmap_vclose(void* pvstate, void* pvhandle);
+void file_reader_mmap_vclose(void* pvstate, void* pvhandle, char* prepipe);
 
 #endif // FILE_READER_MMAP_H
diff --git a/c/input/file_reader_stdio.c b/c/input/file_reader_stdio.c
index 5b7f96167..d605ea4d3 100644
--- a/c/input/file_reader_stdio.c
+++ b/c/input/file_reader_stdio.c
@@ -30,7 +30,7 @@ void* file_reader_stdio_vopen(void* pvstate, char* prepipe, char* filename) {
 }
 
 // ----------------------------------------------------------------
-void file_reader_stdio_vclose(void* pvstate, void* pvhandle) {
+void file_reader_stdio_vclose(void* pvstate, void* pvhandle, char* prepipe) {
 	FILE* input_stream = pvhandle;
 	if (input_stream != stdin)
 		fclose(input_stream);
diff --git a/c/input/file_reader_stdio.h b/c/input/file_reader_stdio.h
index 893c9056e..64146e4ea 100644
--- a/c/input/file_reader_stdio.h
+++ b/c/input/file_reader_stdio.h
@@ -6,6 +6,6 @@
 #define FILE_READER_STDIO_H
 
 void* file_reader_stdio_vopen(void* pvstate, char* prepipe, char* file_name);
-void file_reader_stdio_vclose(void* pvstate, void* pvhandle);
+void file_reader_stdio_vclose(void* pvstate, void* pvhandle, char* prepipe);
 
 #endif // FILE_READER_STDIO_H
diff --git a/c/input/lrec_reader.h b/c/input/lrec_reader.h
index fd3d7e8b2..7274c6765 100644
--- a/c/input/lrec_reader.h
+++ b/c/input/lrec_reader.h
@@ -8,7 +8,7 @@
 
 // The void* pvhandle is either FILE* for stdio readers or file_reader_mmap_state_t* for mmap readers.
 typedef void*   lrec_reader_open_func_t(void* pvstate, char* prepipe, char* filename);
-typedef void    lrec_reader_close_func_t(void* pvstate, void* pvhandle);
+typedef void    lrec_reader_close_func_t(void* pvstate, void* pvhandle, char* prepipe);
 typedef lrec_t* lrec_reader_process_func_t(void* pvstate, void* pvhandle, context_t* pctx);
 typedef void    lrec_reader_sof_func_t(void* pvstate);
 typedef void    lrec_reader_free_func_t(void* pvstate);
diff --git a/c/input/lrec_reader_in_memory.c b/c/input/lrec_reader_in_memory.c
index 4a282db08..d795c908f 100644
--- a/c/input/lrec_reader_in_memory.c
+++ b/c/input/lrec_reader_in_memory.c
@@ -14,7 +14,7 @@ static void    lrec_reader_in_memory_free(void* pvstate);
 static void    lrec_reader_in_memory_sof(void* pvstate);
 static lrec_t* lrec_reader_in_memory_process(void* pvstate, void* pvhandle, context_t* pctx);
 static void*   lrec_reader_in_memory_vopen(void* pvstate, char* prepipe, char* filename);
-static void    lrec_reader_in_memory_vclose(void* pvstate, void* pvhandle);
+static void    lrec_reader_in_memory_vclose(void* pvstate, void* pvhandle, char* prepipe);
 
 // ----------------------------------------------------------------
 lrec_reader_t* lrec_reader_in_memory_alloc(sllv_t* precords) {
@@ -56,5 +56,5 @@ static void* lrec_reader_in_memory_vopen(void* pvstate, char* prepipe, char* fil
 	return NULL;
 }
 
-static void lrec_reader_in_memory_vclose(void* pvstate, void* pvhandle) {
+static void lrec_reader_in_memory_vclose(void* pvstate, void* pvhandle, char* prepipe) {
 }
diff --git a/c/input/lrec_reader_stdio_csv.c b/c/input/lrec_reader_stdio_csv.c
index a75c38cd3..caa52158c 100644
--- a/c/input/lrec_reader_stdio_csv.c
+++ b/c/input/lrec_reader_stdio_csv.c
@@ -78,7 +78,7 @@ static lrec_t* paste_indices_and_data(lrec_reader_stdio_csv_state_t* pstate, rsl
 static lrec_t* paste_header_and_data(lrec_reader_stdio_csv_state_t* pstate, rslls_t* pdata_fields,
 	context_t* pctx);
 static void*   lrec_reader_stdio_csv_open(void* pvstate, char* prepipe, char* filename);
-static void    lrec_reader_stdio_csv_close(void* pvstate, void* pvhandle);
+static void    lrec_reader_stdio_csv_close(void* pvstate, void* pvhandle, char* prepipe);
 
 // ----------------------------------------------------------------
 lrec_reader_t* lrec_reader_stdio_csv_alloc(char* irs, char* ifs, int use_implicit_header) {
@@ -377,7 +377,7 @@ static void* lrec_reader_stdio_csv_open(void* pvstate, char* prepipe, char* file
 	return NULL;
 }
 
-static void lrec_reader_stdio_csv_close(void* pvstate, void* pvhandle) {
+static void lrec_reader_stdio_csv_close(void* pvstate, void* pvhandle, char* prepipe) {
 	lrec_reader_stdio_csv_state_t* pstate = pvstate;
-	pstate->pfr->pbr->pclose_func(pstate->pfr->pbr);
+	pstate->pfr->pbr->pclose_func(pstate->pfr->pbr, prepipe);
 }
diff --git a/c/input/mmap_byte_reader.c b/c/input/mmap_byte_reader.c
index f3d45a53d..d61b60218 100644
--- a/c/input/mmap_byte_reader.c
+++ b/c/input/mmap_byte_reader.c
@@ -19,7 +19,7 @@ typedef struct _mmap_byte_reader_state_t {
 
 static int  mmap_byte_reader_open_func(struct _byte_reader_t* pbr, char* prepipe, char* filename);
 static int  mmap_byte_reader_read_func(struct _byte_reader_t* pbr);
-static void mmap_byte_reader_close_func(struct _byte_reader_t* pbr);
+static void mmap_byte_reader_close_func(struct _byte_reader_t* pbr, char* prepipe);
 
 // ----------------------------------------------------------------
 byte_reader_t* mmap_byte_reader_alloc() {
@@ -88,7 +88,7 @@ static int mmap_byte_reader_read_func(struct _byte_reader_t* pbr) {
 	}
 }
 
-static void mmap_byte_reader_close_func(struct _byte_reader_t* pbr) {
+static void mmap_byte_reader_close_func(struct _byte_reader_t* pbr, char* prepipe) {
 	mmap_byte_reader_state_t* pstate = pbr->pvstate;
 	if (close(pstate->fd) < 0) {
 		perror("close");
diff --git a/c/input/stdio_byte_reader.c b/c/input/stdio_byte_reader.c
index 024ea4fcd..8bf34bf6e 100644
--- a/c/input/stdio_byte_reader.c
+++ b/c/input/stdio_byte_reader.c
@@ -11,7 +11,7 @@ typedef struct _stdio_byte_reader_state_t {
 
 static int stdio_byte_reader_open_func(struct _byte_reader_t* pbr, char* prepipe, char* filename);
 static int stdio_byte_reader_read_func(struct _byte_reader_t* pbr);
-static void stdio_byte_reader_close_func(struct _byte_reader_t* pbr);
+static void stdio_byte_reader_close_func(struct _byte_reader_t* pbr, char* prepipe);
 
 // ----------------------------------------------------------------
 byte_reader_t* stdio_byte_reader_alloc() {
@@ -68,7 +68,8 @@ static int stdio_byte_reader_read_func(struct _byte_reader_t* pbr) {
 	return c;
 }
 
-static void stdio_byte_reader_close_func(struct _byte_reader_t* pbr) {
+static void stdio_byte_reader_close_func(struct _byte_reader_t* pbr, char* prepipe) {
+	// xxx
 	stdio_byte_reader_state_t* pstate = pbr->pvstate;
 	if (pstate->fp != stdin)
 		fclose(pstate->fp);
diff --git a/c/input/string_byte_reader.c b/c/input/string_byte_reader.c
index 324dadca0..7d2ad836e 100644
--- a/c/input/string_byte_reader.c
+++ b/c/input/string_byte_reader.c
@@ -10,7 +10,7 @@ typedef struct _string_byte_reader_state_t {
 
 static int  string_byte_reader_open_func(struct _byte_reader_t* pbr, char* prepipe, char* backing);
 static int  string_byte_reader_read_func(struct _byte_reader_t* pbr);
-static void string_byte_reader_close_func(struct _byte_reader_t* pbr);
+static void string_byte_reader_close_func(struct _byte_reader_t* pbr, char* prepipe);
 
 // ----------------------------------------------------------------
 byte_reader_t* string_byte_reader_alloc() {
@@ -48,6 +48,6 @@ static int string_byte_reader_read_func(struct _byte_reader_t* pbr) {
 	}
 }
 
-static void string_byte_reader_close_func(struct _byte_reader_t* pbr) {
+static void string_byte_reader_close_func(struct _byte_reader_t* pbr, char* prepipe) {
 	pbr->pvstate = NULL;
 }
diff --git a/c/mapping/mapper_join.c b/c/mapping/mapper_join.c
index 224a90a0b..7fe27c3de 100644
--- a/c/mapping/mapper_join.c
+++ b/c/mapping/mapper_join.c
@@ -236,7 +236,7 @@ static void mapper_join_free(void* pvstate) {
 	if (pstate->popts->poutput_join_field_names != NULL)
 		slls_free(pstate->popts->poutput_join_field_names);
 	if (pstate->pjoin_bucket_keeper != NULL)
-		join_bucket_keeper_free(pstate->pjoin_bucket_keeper);
+		join_bucket_keeper_free(pstate->pjoin_bucket_keeper, pstate->popts->prepipe);
 }
 
 // ----------------------------------------------------------------
@@ -504,5 +504,5 @@ static void ingest_left_file(mapper_join_state_t* pstate) {
 		}
 	}
 
-	plrec_reader->pclose_func(plrec_reader->pvstate, pvhandle);
+	plrec_reader->pclose_func(plrec_reader->pvstate, pvhandle, pstate->popts->prepipe);
 }
diff --git a/c/stream/stream.c b/c/stream/stream.c
index 80d39cb44..2c44ba3bb 100644
--- a/c/stream/stream.c
+++ b/c/stream/stream.c
@@ -74,7 +74,7 @@ static int do_file_chained(char* prepipe, char* filename, context_t* pctx,
 		drive_lrec(pinrec, pctx, pmapper_list->phead, plrec_writer, output_stream);
 	}
 
-	plrec_reader->pclose_func(plrec_reader->pvstate, pvhandle);
+	plrec_reader->pclose_func(plrec_reader->pvstate, pvhandle, prepipe);
 	return 1;
 }
 
diff --git a/c/todo.txt b/c/todo.txt
index 6951a090a..723ae1820 100644
--- a/c/todo.txt
+++ b/c/todo.txt
@@ -45,6 +45,8 @@ TOP OF LIST
   - fminus -> python too
   - mlr as data prep clean
 
+* mixed-format joins ...
+
 ----------------------------------------------------------------
 COOKBOOK/FAQ/ETC.:
 
diff --git a/c/unit_test/test_byte_readers.c b/c/unit_test/test_byte_readers.c
index e66d88cc6..196761979 100644
--- a/c/unit_test/test_byte_readers.c
+++ b/c/unit_test/test_byte_readers.c
@@ -22,14 +22,14 @@ static char* test_string_byte_reader() {
 	mu_assert_lf(pbr->pread_func(pbr) == EOF);
 	mu_assert_lf(pbr->pread_func(pbr) == EOF);
 	mu_assert_lf(pbr->pread_func(pbr) == EOF);
-	pbr->pclose_func(pbr);
+	pbr->pclose_func(pbr, NULL);
 
 	ok = pbr->popen_func(pbr, NULL, "a");
 	mu_assert_lf(ok == TRUE);
 	mu_assert_lf(pbr->pread_func(pbr) == 'a');
 	mu_assert_lf(pbr->pread_func(pbr) == EOF);
 	mu_assert_lf(pbr->pread_func(pbr) == EOF);
-	pbr->pclose_func(pbr);
+	pbr->pclose_func(pbr, NULL);
 
 	ok = pbr->popen_func(pbr, NULL, "abc");
 	mu_assert_lf(ok == TRUE);
@@ -38,7 +38,7 @@ static char* test_string_byte_reader() {
 	mu_assert_lf(pbr->pread_func(pbr) == 'c');
 	mu_assert_lf(pbr->pread_func(pbr) == EOF);
 	mu_assert_lf(pbr->pread_func(pbr) == EOF);
-	pbr->pclose_func(pbr);
+	pbr->pclose_func(pbr, NULL);
 
 	return NULL;
 }
diff --git a/c/unit_test/test_peek_file_reader.c b/c/unit_test/test_peek_file_reader.c
index 22724c5ef..5271f027c 100644
--- a/c/unit_test/test_peek_file_reader.c
+++ b/c/unit_test/test_peek_file_reader.c
@@ -23,7 +23,7 @@ static char* test_empty() {
 	mu_assert_lf(pfr_peek_char(pfr) == (char)EOF); // char defaults to unsigned on some platforms
 	mu_assert_lf(pfr_read_char(pfr) == (char)EOF);
 
-	pbr->pclose_func(pbr);
+	pbr->pclose_func(pbr, NULL);
 	pfr_free(pfr);
 
 	return NULL;
@@ -62,7 +62,7 @@ static char* test_non_empty() {
 	pfr_print(pfr); pfr_advance_by(pfr, 5);
 	pfr_print(pfr); mu_assert_lf(pfr_read_char(pfr) == '\n');
 
-	pbr->pclose_func(pbr);
+	pbr->pclose_func(pbr, NULL);
 	pfr_free(pfr);
 
 	return NULL;