Simplify streaming API and improve pretty printing

This removes the obligation from the caller to correctly maintain flags to
describe the current anonymous context, instead making the writer handle this
itself as much as possible.  Flags remain for the cases the writer can not
infer from context: the start of anonymous subject and object nodes.

9 files changed, 374 insertions, 174 deletions

diff --git a/NEWS b/NEWS
index 48b588c0..7d95fb17 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,7 @@ serd (1.0.1) unstable;
   * Remove serd_uri_to_path()
   * Remove useless character counting from API
   * Rename SerdChunk to SerdStringView
+  * Simplify streaming API and improve pretty printing
   * Simplify writer style options
   * Use a fixed-size reader stack
   * Use char* for strings in public API
diff --git a/include/serd/serd.h b/include/serd/serd.h
index 7b279517..3d06c4a0 100644
--- a/include/serd/serd.h
+++ b/include/serd/serd.h
@@ -132,14 +132,11 @@ typedef enum {
 
 /// Flags indicating inline abbreviation information for a statement
 typedef enum {
-  SERD_EMPTY_S      = 1u << 1u, ///< Empty blank node subject
-  SERD_EMPTY_O      = 1u << 2u, ///< Empty blank node object
-  SERD_ANON_S_BEGIN = 1u << 3u, ///< Start of anonymous subject
-  SERD_ANON_O_BEGIN = 1u << 4u, ///< Start of anonymous object
-  SERD_ANON_CONT    = 1u << 5u, ///< Continuation of anonymous node
-  SERD_LIST_S_BEGIN = 1u << 6u, ///< Start of list subject
-  SERD_LIST_O_BEGIN = 1u << 7u, ///< Start of list object
-  SERD_LIST_CONT    = 1u << 8u  ///< Continuation of list
+  SERD_EMPTY_S      = 1u << 0u, ///< Empty blank node subject
+  SERD_ANON_S_BEGIN = 1u << 1u, ///< Start of anonymous subject
+  SERD_ANON_O_BEGIN = 1u << 2u, ///< Start of anonymous object
+  SERD_LIST_S_BEGIN = 1u << 3u, ///< Start of list subject
+  SERD_LIST_O_BEGIN = 1u << 4u, ///< Start of list object
 } SerdStatementFlag;
 
 /// Bitwise OR of SerdStatementFlag values
diff --git a/src/n3.c b/src/n3.c
index 65ed03ab..7c0d2f4f 100644
--- a/src/n3.c
+++ b/src/n3.c
@@ -1030,13 +1030,15 @@ read_blankName(SerdReader* reader)
 static SerdStatus
 read_anon(SerdReader* reader, ReadContext ctx, bool subject, SerdNode** dest)
 {
-  const SerdStatementFlags old_flags = *ctx.flags;
-  bool                     empty     = false;
   eat_byte_safe(reader, '[');
-  if ((empty = peek_delim(reader, ']'))) {
-    *ctx.flags |= (subject) ? SERD_EMPTY_S : SERD_EMPTY_O;
+
+  const SerdStatementFlags old_flags = *ctx.flags;
+  const bool               empty     = peek_delim(reader, ']');
+
+  if (subject) {
+    *ctx.flags |= empty ? SERD_EMPTY_S : SERD_ANON_S_BEGIN;
   } else {
-    *ctx.flags |= (subject) ? SERD_ANON_S_BEGIN : SERD_ANON_O_BEGIN;
+    *ctx.flags |= SERD_ANON_O_BEGIN;
     if (peek_delim(reader, '=')) {
       if (!(*dest = read_blankName(reader)) || !eat_delim(reader, ';')) {
         return SERD_ERR_BAD_SYNTAX;
@@ -1048,26 +1050,35 @@ read_anon(SerdReader* reader, ReadContext ctx, bool subject, SerdNode** dest)
     *dest = blank_id(reader);
   }
 
+  // Emit statement with this anonymous object first
   SerdStatus st = SERD_SUCCESS;
   if (ctx.subject) {
     TRY(st, emit_statement(reader, ctx, *dest));
   }
 
+  // Switch the subject to the anonymous node and read its description
   ctx.subject = *dest;
   if (!empty) {
-    *ctx.flags &= ~(unsigned)SERD_LIST_CONT;
-    if (!subject) {
-      *ctx.flags |= SERD_ANON_CONT;
-    }
     bool ate_dot_in_list = false;
-    read_predicateObjectList(reader, ctx, &ate_dot_in_list);
+    st = read_predicateObjectList(reader, ctx, &ate_dot_in_list);
+    if (st > SERD_FAILURE) {
+      return st;
+    }
+
     if (ate_dot_in_list) {
       return r_err(reader, SERD_ERR_BAD_SYNTAX, "`.' inside blank\n");
     }
+
     read_ws_star(reader);
-    serd_sink_write_end(reader->sink, *dest);
     *ctx.flags = old_flags;
   }
+
+  if (!(subject && empty)) {
+    if ((st = serd_sink_write_end(reader->sink, *dest))) {
+      return st;
+    }
+  }
+
   return (eat_byte_check(reader, ']') == ']') ? SERD_SUCCESS
                                               : SERD_ERR_BAD_SYNTAX;
 }
@@ -1250,9 +1261,8 @@ read_predicateObjectList(SerdReader* reader, ReadContext ctx, bool* ate_dot)
 }
 
 static SerdStatus
-end_collection(SerdReader* reader, ReadContext ctx, SerdStatus st)
+end_collection(SerdReader* reader, SerdStatus st)
 {
-  *ctx.flags &= ~(unsigned)SERD_LIST_CONT;
   if (!st) {
     return (eat_byte_check(reader, ')') == ')') ? SERD_SUCCESS
                                                 : SERD_ERR_BAD_SYNTAX;
@@ -1271,13 +1281,12 @@ read_collection(SerdReader* reader, ReadContext ctx, SerdNode** dest)
     // subject predicate _:head
     *ctx.flags |= (end ? 0 : SERD_LIST_O_BEGIN);
     TRY(st, emit_statement(reader, ctx, *dest));
-    *ctx.flags |= SERD_LIST_CONT;
   } else {
     *ctx.flags |= (end ? 0 : SERD_LIST_S_BEGIN);
   }
 
   if (end) {
-    return end_collection(reader, ctx, st);
+    return end_collection(reader, st);
   }
 
   /* The order of node allocation here is necessarily not in stack order,
@@ -1297,7 +1306,7 @@ read_collection(SerdReader* reader, ReadContext ctx, SerdNode** dest)
     ctx.predicate = reader->rdf_first;
     bool ate_dot  = false;
     if ((st = read_object(reader, &ctx, true, &ate_dot)) || ate_dot) {
-      return end_collection(reader, ctx, st);
+      return end_collection(reader, st);
     }
 
     if (!(end = peek_delim(reader, ')'))) {
@@ -1311,7 +1320,6 @@ read_collection(SerdReader* reader, ReadContext ctx, SerdNode** dest)
     }
 
     // _:node rdf:rest _:rest
-    *ctx.flags |= SERD_LIST_CONT;
     ctx.predicate = reader->rdf_rest;
     TRY(st, emit_statement(reader, ctx, (end ? reader->rdf_nil : rest)));
 
@@ -1320,7 +1328,7 @@ read_collection(SerdReader* reader, ReadContext ctx, SerdNode** dest)
     node        = ctx.subject; // invariant
   }
 
-  return end_collection(reader, ctx, st);
+  return end_collection(reader, st);
 }
 
 static SerdStatus
@@ -1330,7 +1338,7 @@ read_subject(SerdReader* reader, ReadContext ctx, SerdNode** dest, int* s_type)
   bool       ate_dot = false;
   switch ((*s_type = peek_byte(reader))) {
   case '[':
-    read_anon(reader, ctx, true, dest);
+    st = read_anon(reader, ctx, true, dest);
     break;
   case '(':
     st = read_collection(reader, ctx, dest);
diff --git a/src/reader.c b/src/reader.c
index 351428fc..8b687864 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -129,7 +129,7 @@ emit_statement(SerdReader* reader, ReadContext ctx, SerdNode* o)
   const SerdStatus st =
     serd_sink_write_statement(reader->sink, *ctx.flags, &statement);
 
-  *ctx.flags &= SERD_ANON_CONT | SERD_LIST_CONT; // Preserve only cont flags
+  *ctx.flags = 0;
   return st;
 }
 
diff --git a/src/stack.h b/src/stack.h
index 62f3402b..f6d33f51 100644
--- a/src/stack.h
+++ b/src/stack.h
@@ -46,6 +46,12 @@ serd_stack_new(size_t size)
   return stack;
 }
 
+static inline void
+serd_stack_clear(SerdStack* stack)
+{
+  stack->size = SERD_STACK_BOTTOM;
+}
+
 static inline bool
 serd_stack_is_empty(SerdStack* stack)
 {
diff --git a/src/writer.c b/src/writer.c
index 4f4a76df..31c8c0a1 100644
--- a/src/writer.c
+++ b/src/writer.c
@@ -32,56 +32,75 @@
 #include <stdlib.h>
 #include <string.h>
 
+typedef enum {
+  CTX_NAMED, ///< Normal non-anonymous context
+  CTX_BLANK, ///< Anonymous blank node
+  CTX_LIST   ///< Anonymous list
+} ContextType;
+
 typedef struct {
-  SerdNode* graph;
-  SerdNode* subject;
-  SerdNode* predicate;
+  ContextType type;
+  SerdNode*   graph;
+  SerdNode*   subject;
+  SerdNode*   predicate;
+  bool        indented_object;
 } WriteContext;
 
-static const WriteContext WRITE_CONTEXT_NULL = {NULL, NULL, NULL};
+static const WriteContext WRITE_CONTEXT_NULL = {CTX_NAMED,
+                                                NULL,
+                                                NULL,
+                                                NULL,
+                                                false};
 
 typedef enum {
-  SEP_NONE,
+  SEP_NONE,        ///< Placeholder for nodes or nothing
   SEP_END_S,       ///< End of a subject ('.')
   SEP_END_P,       ///< End of a predicate (';')
   SEP_END_O,       ///< End of an object (',')
   SEP_S_P,         ///< Between a subject and predicate (whitespace)
   SEP_P_O,         ///< Between a predicate and object (whitespace)
   SEP_ANON_BEGIN,  ///< Start of anonymous node ('[')
+  SEP_ANON_S_P,    ///< Between start of anonymous node and predicate
   SEP_ANON_END,    ///< End of anonymous node (']')
   SEP_LIST_BEGIN,  ///< Start of list ('(')
   SEP_LIST_SEP,    ///< List separator (whitespace)
   SEP_LIST_END,    ///< End of list (')')
   SEP_GRAPH_BEGIN, ///< Start of graph ('{')
   SEP_GRAPH_END,   ///< End of graph ('}')
-  SEP_URI_BEGIN,   ///< URI start quote ('<')
-  SEP_URI_END      ///< URI end quote ('>')
 } Sep;
 
+typedef uint32_t SepMask; ///< Bitfield of separator flags
+
+#define SEP_ALL ((SepMask)-1)
+#define M(s) (1U << (s))
+
 typedef struct {
-  const char* str;              ///< Sep string
-  uint8_t     len;              ///< Length of sep string
-  uint8_t     space_before;     ///< Newline before sep
-  uint8_t     space_after_node; ///< Newline after sep if after node
-  uint8_t     space_after_sep;  ///< Newline after sep if after sep
+  const char* str;             ///< Sep string
+  size_t      len;             ///< Length of sep string
+  int         indent;          ///< Indent delta
+  SepMask     pre_space_after; ///< Leading space if after given seps
+  SepMask     pre_line_after;  ///< Leading newline if after given seps
+  SepMask     post_line_after; ///< Trailing newline if after given seps
 } SepRule;
 
-static const SepRule rules[] = {{NULL, 0, 0, 0, 0},
-                                {" .\n\n", 4, 0, 0, 0},
-                                {" ;", 2, 0, 1, 1},
-                                {" ,", 2, 0, 1, 0},
-                                {NULL, 0, 0, 1, 0},
-                                {" ", 1, 0, 0, 0},
-                                {"[", 1, 0, 1, 1},
-                                {"]", 1, 1, 0, 0},
-                                {"(", 1, 0, 0, 0},
-                                {NULL, 0, 0, 1, 0},
-                                {")", 1, 1, 0, 0},
-                                {" {", 2, 0, 1, 1},
-                                {" }", 2, 0, 1, 1},
-                                {"<", 1, 0, 0, 0},
-                                {">", 1, 0, 0, 0},
-                                {"\n", 1, 0, 1, 0}};
+static const SepRule rules[] = {
+  {"", 0, +0, SEP_NONE, SEP_NONE, SEP_NONE},
+  {".\n", 2, -1, SEP_ALL, SEP_NONE, SEP_NONE},
+  {";", 1, +0, SEP_ALL, SEP_NONE, SEP_ALL},
+  {",", 1, +0, SEP_ALL, SEP_NONE, ~(M(SEP_ANON_END) | M(SEP_LIST_END))},
+  {"", 0, +1, SEP_NONE, SEP_NONE, SEP_ALL},
+  {" ", 1, +0, SEP_NONE, SEP_NONE, SEP_NONE},
+  {"[", 1, +1, M(SEP_END_O), SEP_NONE, SEP_NONE},
+  {"", 0, +0, SEP_NONE, SEP_ALL, SEP_NONE},
+  {"]", 1, -1, SEP_NONE, ~M(SEP_ANON_BEGIN), SEP_NONE},
+  {"(", 1, +1, M(SEP_END_O), SEP_NONE, SEP_ALL},
+  {"", 0, +0, SEP_NONE, SEP_ALL, SEP_NONE},
+  {")", 1, -1, SEP_NONE, SEP_ALL, SEP_NONE},
+  {"{", 1, +1, SEP_ALL, SEP_NONE, SEP_NONE},
+  {"}", 1, -1, SEP_NONE, SEP_NONE, SEP_ALL},
+  {"<", 1, +0, SEP_NONE, SEP_NONE, SEP_NONE},
+  {">", 1, +0, SEP_NONE, SEP_NONE, SEP_NONE},
+};
 
 struct SerdWriterImpl {
   SerdWorld*      world;
@@ -97,12 +116,10 @@ struct SerdWriterImpl {
   SerdErrorFunc   error_func;
   void*           error_handle;
   WriteContext    context;
-  SerdNode*       list_subj;
-  unsigned        list_depth;
-  unsigned        indent;
   char*           bprefix;
   size_t          bprefix_len;
   Sep             last_sep;
+  int             indent;
   bool            empty;
 };
 
@@ -131,12 +148,45 @@ supports_uriref(const SerdWriter* writer)
   return writer->syntax == SERD_TURTLE || writer->syntax == SERD_TRIG;
 }
 
-static inline WriteContext*
-anon_stack_top(SerdWriter* writer)
+static SerdStatus
+free_context(SerdWriter* writer)
+{
+  serd_node_free(writer->context.graph);
+  serd_node_free(writer->context.subject);
+  serd_node_free(writer->context.predicate);
+  return SERD_SUCCESS;
+}
+
+static inline SerdStatus
+push_context(SerdWriter* writer, const WriteContext new_context)
+{
+  WriteContext* top =
+    (WriteContext*)serd_stack_push(&writer->anon_stack, sizeof(WriteContext));
+
+  if (!top) {
+    return SERD_ERR_OVERFLOW;
+  }
+
+  *top            = writer->context;
+  writer->context = new_context;
+  return SERD_SUCCESS;
+}
+
+static inline void
+pop_context(SerdWriter* writer)
 {
   assert(!serd_stack_is_empty(&writer->anon_stack));
-  return (WriteContext*)(writer->anon_stack.buf + writer->anon_stack.size -
-                         sizeof(WriteContext));
+
+  if (writer->context.indented_object && writer->indent > 0) {
+    --writer->indent;
+  }
+
+  free_context(writer);
+  writer->context =
+    *(WriteContext*)(writer->anon_stack.buf + writer->anon_stack.size -
+                     sizeof(WriteContext));
+
+  serd_stack_pop(&writer->anon_stack, sizeof(WriteContext));
 }
 
 static inline SerdNode*
@@ -429,7 +479,7 @@ static void
 write_newline(SerdWriter* writer)
 {
   sink("\n", 1, writer);
-  for (unsigned i = 0; i < writer->indent; ++i) {
+  for (int i = 0; i < writer->indent; ++i) {
     sink("\t", 1, writer);
   }
 }
@@ -438,47 +488,67 @@ static bool
 write_sep(SerdWriter* writer, const Sep sep)
 {
   const SepRule* rule = &rules[sep];
-  if (rule->space_before) {
+
+  // Adjust indent, but tolerate if it would become negative
+  if ((rule->pre_line_after & (1u << writer->last_sep) ||
+       (rule->post_line_after & (1u << writer->last_sep)))) {
+    writer->indent = ((rule->indent >= 0 || writer->indent >= -rule->indent)
+                        ? writer->indent + rule->indent
+                        : 0);
+  }
+
+  // Write newline or space before separator if necessary
+  if (rule->pre_line_after & (1u << writer->last_sep)) {
     write_newline(writer);
+  } else if (rule->pre_space_after & (1u << writer->last_sep)) {
+    sink(" ", 1, writer);
   }
 
-  if (rule->str) {
+  // Write actual separator string
+  if (rule->len > 0) {
     sink(rule->str, rule->len, writer);
   }
 
-  if ((writer->last_sep && rule->space_after_sep) ||
-      (!writer->last_sep && rule->space_after_node)) {
+  // Write newline after separator if necessary
+  if (rule->post_line_after & (1u << writer->last_sep)) {
     write_newline(writer);
-  } else if (writer->last_sep && rule->space_after_node) {
-    sink(" ", 1, writer);
+    writer->last_sep = SEP_NONE;
+  } else {
+    writer->last_sep = sep;
+  }
+
+  if (sep == SEP_END_S) {
+    writer->indent = 0;
   }
 
-  writer->last_sep = sep;
   return true;
 }
 
 static SerdStatus
 reset_context(SerdWriter* writer, bool graph)
 {
+  // Free any lingering contexts in case there was an error
+  while (!serd_stack_is_empty(&writer->anon_stack)) {
+    pop_context(writer);
+  }
+
   if (graph && writer->context.graph) {
     memset(writer->context.graph, 0, sizeof(SerdNode));
   }
+
   if (writer->context.subject) {
     memset(writer->context.subject, 0, sizeof(SerdNode));
   }
+
   if (writer->context.predicate) {
     memset(writer->context.predicate, 0, sizeof(SerdNode));
   }
-  writer->empty = false;
-  return SERD_SUCCESS;
-}
 
-static SerdStatus
-free_context(SerdWriter* writer)
-{
-  serd_node_free(writer->context.graph);
-  serd_node_free(writer->context.subject);
-  serd_node_free(writer->context.predicate);
+  writer->context.indented_object = false;
+  writer->empty                   = false;
+
+  serd_stack_clear(&writer->anon_stack);
+
   return SERD_SUCCESS;
 }
 
@@ -497,6 +567,8 @@ write_literal(SerdWriter*        writer,
               const SerdNode*    node,
               SerdStatementFlags flags)
 {
+  writer->last_sep = SEP_NONE;
+
   const SerdNode* datatype = serd_node_datatype(node);
   const SerdNode* lang     = serd_node_language(node);
   const char*     node_str = serd_node_string(node);
@@ -559,17 +631,15 @@ write_uri_node(SerdWriter* const        writer,
                const SerdField          field,
                const SerdStatementFlags flags)
 {
-  const SerdNode* prefix = NULL;
-  SerdStringView  suffix = {NULL, 0};
-
   if (is_inline_start(writer, field, flags)) {
-    ++writer->indent;
     write_sep(writer, SEP_ANON_BEGIN);
-    sink("== ", 3, writer);
+    sink(" == ", 4, writer);
   }
 
-  const char* node_str   = serd_node_string(node);
-  const bool  has_scheme = serd_uri_string_has_scheme(node_str);
+  const SerdNode* prefix     = NULL;
+  SerdStringView  suffix     = {NULL, 0};
+  const char*     node_str   = serd_node_string(node);
+  const bool      has_scheme = serd_uri_string_has_scheme(node_str);
   if (supports_abbrev(writer)) {
     if (field == SERD_PREDICATE &&
         serd_node_equals(node, writer->world->rdf_type)) {
@@ -600,7 +670,7 @@ write_uri_node(SerdWriter* const        writer,
     return false;
   }
 
-  write_sep(writer, SEP_URI_BEGIN);
+  sink("<", 1, writer);
   if (!(writer->flags & SERD_WRITE_UNRESOLVED) &&
       serd_env_base_uri(writer->env)) {
     const SerdURIView  base_uri = serd_env_base_uri_view(writer->env);
@@ -618,11 +688,10 @@ write_uri_node(SerdWriter* const        writer,
   } else {
     write_uri_from_node(writer, node);
   }
-  write_sep(writer, SEP_URI_END);
+  sink(">", 1, writer);
 
   if (is_inline_start(writer, field, flags)) {
     sink(" ;", 2, writer);
-    write_newline(writer);
   }
 
   return true;
@@ -634,7 +703,7 @@ write_curie(SerdWriter* const        writer,
             const SerdField          field,
             const SerdStatementFlags flags)
 {
-  const char* node_str = serd_node_string(node);
+  writer->last_sep = SEP_NONE;
 
   SerdStringView prefix = {NULL, 0};
   SerdStringView suffix = {NULL, 0};
@@ -643,26 +712,26 @@ write_curie(SerdWriter* const        writer,
   case SERD_NTRIPLES:
   case SERD_NQUADS:
     if ((st = serd_env_expand_in_place(writer->env, node, &prefix, &suffix))) {
-      serd_world_errorf(
-        writer->world, st, "undefined namespace prefix `%s'\n", node_str);
+      serd_world_errorf(writer->world,
+                        st,
+                        "undefined namespace prefix `%s'\n",
+                        serd_node_string(node));
       return false;
     }
-    write_sep(writer, SEP_URI_BEGIN);
+    sink("<", 1, writer);
     write_uri(writer, prefix.buf, prefix.len);
     write_uri(writer, suffix.buf, suffix.len);
-    write_sep(writer, SEP_URI_END);
+    sink(">", 1, writer);
     break;
   case SERD_TURTLE:
   case SERD_TRIG:
     if (is_inline_start(writer, field, flags)) {
-      ++writer->indent;
       write_sep(writer, SEP_ANON_BEGIN);
-      sink("== ", 3, writer);
+      sink(" == ", 4, writer);
     }
-    write_lname(writer, node_str, node->n_bytes);
+    write_lname(writer, serd_node_string(node), node->n_bytes);
     if (is_inline_start(writer, field, flags)) {
       sink(" ;", 2, writer);
-      write_newline(writer);
     }
   }
   return true;
@@ -677,26 +746,16 @@ write_blank(SerdWriter* const        writer,
   const char* node_str = serd_node_string(node);
   if (supports_abbrev(writer)) {
     if (is_inline_start(writer, field, flags)) {
-      ++writer->indent;
       return write_sep(writer, SEP_ANON_BEGIN);
     }
 
-    if (field == SERD_SUBJECT && (flags & SERD_LIST_S_BEGIN)) {
-      assert(writer->list_depth == 0);
-      serd_node_set(&writer->list_subj, node);
-      ++writer->list_depth;
-      ++writer->indent;
+    if ((field == SERD_SUBJECT && (flags & SERD_LIST_S_BEGIN)) ||
+        (field == SERD_OBJECT && (flags & SERD_LIST_O_BEGIN))) {
       return write_sep(writer, SEP_LIST_BEGIN);
     }
 
-    if (field == SERD_OBJECT && (flags & SERD_LIST_O_BEGIN)) {
-      ++writer->indent;
-      ++writer->list_depth;
-      return write_sep(writer, SEP_LIST_BEGIN);
-    }
-
-    if ((field == SERD_SUBJECT && (flags & SERD_EMPTY_S)) ||
-        (field == SERD_OBJECT && (flags & SERD_EMPTY_O))) {
+    if (field == SERD_SUBJECT && (flags & SERD_EMPTY_S)) {
+      writer->last_sep = SEP_NONE; // Treat "[]" like a node
       return sink("[]", 2, writer) == 2;
     }
   }
@@ -711,6 +770,7 @@ write_blank(SerdWriter* const        writer,
     sink(node_str, node->n_bytes, writer);
   }
 
+  writer->last_sep = SEP_NONE;
   return true;
 }
 
@@ -720,23 +780,18 @@ write_node(SerdWriter*        writer,
            const SerdField    field,
            SerdStatementFlags flags)
 {
-  bool ret = false;
   switch (node->type) {
   case SERD_LITERAL:
-    ret = write_literal(writer, node, flags);
-    break;
+    return write_literal(writer, node, flags);
   case SERD_URI:
-    ret = write_uri_node(writer, node, field, flags);
-    break;
+    return write_uri_node(writer, node, field, flags);
   case SERD_CURIE:
-    ret = write_curie(writer, node, field, flags);
-    break;
+    return write_curie(writer, node, field, flags);
   case SERD_BLANK:
-    ret = write_blank(writer, node, field, flags);
-    break;
+    return write_blank(writer, node, field, flags);
   }
-  writer->last_sep = SEP_NONE;
-  return ret;
+
+  return false;
 }
 
 static inline bool
@@ -760,14 +815,14 @@ write_list_obj(SerdWriter*        writer,
                const SerdNode*    object)
 {
   if (serd_node_equals(object, writer->world->rdf_nil)) {
-    --writer->indent;
     write_sep(writer, SEP_LIST_END);
     return true;
   }
 
   if (serd_node_equals(predicate, writer->world->rdf_first)) {
-    write_sep(writer, SEP_LIST_SEP);
     write_node(writer, object, SERD_OBJECT, flags);
+  } else {
+    write_sep(writer, SEP_LIST_SEP);
   }
 
   return false;
@@ -778,6 +833,12 @@ serd_writer_write_statement(SerdWriter*          writer,
                             SerdStatementFlags   flags,
                             const SerdStatement* statement)
 {
+  assert(!((flags & SERD_EMPTY_S) && (flags & SERD_ANON_S_BEGIN)));
+  assert(!((flags & SERD_EMPTY_S) && (flags & SERD_LIST_S_BEGIN)));
+  assert(!((flags & SERD_ANON_S_BEGIN) && (flags & SERD_LIST_S_BEGIN)));
+  assert(!((flags & SERD_ANON_O_BEGIN) && (flags & SERD_LIST_O_BEGIN)));
+
+  SerdStatus            st        = SERD_SUCCESS;
   const SerdNode* const subject   = serd_statement_subject(statement);
   const SerdNode* const predicate = serd_statement_predicate(statement);
   const SerdNode* const object    = serd_statement_object(statement);
@@ -810,47 +871,51 @@ serd_writer_write_statement(SerdWriter*          writer,
 
   if ((graph && !serd_node_equals(graph, writer->context.graph)) ||
       (!graph && ctx(writer, SERD_GRAPH))) {
-    writer->indent = 0;
     if (ctx(writer, SERD_SUBJECT)) {
       write_sep(writer, SEP_END_S);
     }
+
     if (ctx(writer, SERD_GRAPH)) {
       write_sep(writer, SEP_GRAPH_END);
     }
 
+    if (!writer->empty) {
+      write_newline(writer); // Blank line between top level items
+    }
+
     reset_context(writer, true);
+
     if (graph) {
       TRY(write_node(writer, graph, SERD_GRAPH, flags));
-      ++writer->indent;
       write_sep(writer, SEP_GRAPH_BEGIN);
       serd_node_set(&writer->context.graph, graph);
     }
   }
 
-  if ((flags & SERD_LIST_CONT)) {
+  if (writer->context.type == CTX_LIST) {
     if (write_list_obj(writer, flags, predicate, object)) {
       // Reached end of list
-      if (--writer->list_depth == 0 && writer->list_subj) {
-        reset_context(writer, false);
-        serd_node_free(writer->context.subject);
-        writer->context.subject = writer->list_subj;
-        writer->list_subj       = NULL;
-      }
+      pop_context(writer);
       return SERD_SUCCESS;
     }
   } else if (serd_node_equals(subject, writer->context.subject)) {
     if (serd_node_equals(predicate, writer->context.predicate)) {
       // Abbreviate S P
-      if (!(flags & SERD_ANON_O_BEGIN)) {
+      if (!writer->context.indented_object &&
+          !(flags & (SERD_ANON_O_BEGIN | SERD_LIST_O_BEGIN))) {
         ++writer->indent;
+        writer->context.indented_object = true;
       }
+
       write_sep(writer, SEP_END_O);
       write_node(writer, object, SERD_OBJECT, flags);
-      if (!(flags & SERD_ANON_O_BEGIN)) {
-        --writer->indent;
-      }
     } else {
       // Abbreviate S
+      if (writer->context.indented_object && writer->indent > 0) {
+        --writer->indent;
+        writer->context.indented_object = false;
+      }
+
       Sep sep = ctx(writer, SERD_PREDICATE) ? SEP_END_P : SEP_S_P;
       write_sep(writer, sep);
       write_pred(writer, flags, predicate);
@@ -858,22 +923,29 @@ serd_writer_write_statement(SerdWriter*          writer,
     }
   } else {
     // No abbreviation
-    if (ctx(writer, SERD_SUBJECT)) {
-      assert(writer->indent > 0);
+    if (writer->context.indented_object && writer->indent > 0) {
       --writer->indent;
-      if (serd_stack_is_empty(&writer->anon_stack)) {
-        write_sep(writer, SEP_END_S);
+      writer->context.indented_object = false;
+    }
+
+    if (serd_stack_is_empty(&writer->anon_stack)) {
+      if (ctx(writer, SERD_SUBJECT)) {
+        write_sep(writer, SEP_END_S); // Terminate last subject
+      }
+      if (!writer->empty) {
+        write_newline(writer); // Blank line between top level items
       }
-    } else if (!writer->empty) {
-      write_sep(writer, SEP_S_P);
     }
 
-    if (!(flags & SERD_ANON_CONT)) {
+    if (serd_stack_is_empty(&writer->anon_stack)) {
       write_node(writer, subject, SERD_SUBJECT, flags);
-      ++writer->indent;
-      write_sep(writer, SEP_S_P);
+      if (!(flags & (SERD_ANON_S_BEGIN | SERD_LIST_S_BEGIN))) {
+        write_sep(writer, SEP_S_P);
+      } else if (flags & SERD_ANON_S_BEGIN) {
+        write_sep(writer, SEP_ANON_S_P);
+      }
     } else {
-      ++writer->indent;
+      write_sep(writer, SEP_ANON_S_P);
     }
 
     reset_context(writer, false);
@@ -886,21 +958,37 @@ serd_writer_write_statement(SerdWriter*          writer,
     write_node(writer, object, SERD_OBJECT, flags);
   }
 
-  if (flags & (SERD_ANON_S_BEGIN | SERD_ANON_O_BEGIN)) {
-    WriteContext* ctx =
-      (WriteContext*)serd_stack_push(&writer->anon_stack, sizeof(WriteContext));
-    if (!ctx) {
-      return SERD_ERR_OVERFLOW;
+  // Push context for anonymous or list subject if necessary
+  if (flags & (SERD_ANON_S_BEGIN | SERD_LIST_S_BEGIN)) {
+    const bool is_list = (flags & SERD_LIST_S_BEGIN);
+
+    const WriteContext ctx = {is_list ? CTX_LIST : CTX_BLANK,
+                              serd_node_copy(graph),
+                              serd_node_copy(subject),
+                              is_list ? NULL : serd_node_copy(predicate),
+                              false};
+    if ((st = push_context(writer, ctx))) {
+      return st;
     }
+  }
 
-    *ctx                     = writer->context;
-    WriteContext new_context = {
-      serd_node_copy(graph), serd_node_copy(subject), NULL};
-    if ((flags & SERD_ANON_S_BEGIN)) {
-      new_context.predicate = serd_node_copy(predicate);
+  // Push context for anonymous or list object if necessary
+  if (flags & (SERD_ANON_O_BEGIN | SERD_LIST_O_BEGIN)) {
+    const bool is_list = (flags & SERD_LIST_O_BEGIN);
+
+    const WriteContext ctx = {is_list ? CTX_LIST : CTX_BLANK,
+                              serd_node_copy(graph),
+                              serd_node_copy(object),
+                              NULL,
+                              false};
+    if ((st = push_context(writer, ctx))) {
+      return st;
     }
-    writer->context = new_context;
-  } else {
+  }
+
+  if (!(flags & (SERD_ANON_S_BEGIN | SERD_LIST_S_BEGIN | SERD_ANON_O_BEGIN |
+                 SERD_LIST_O_BEGIN))) {
+    // Update current context to this statement
     serd_node_set(&writer->context.graph, graph);
     serd_node_set(&writer->context.subject, subject);
     serd_node_set(&writer->context.predicate, predicate);
@@ -916,20 +1004,18 @@ serd_writer_end_anon(SerdWriter* writer, const SerdNode* node)
     return SERD_SUCCESS;
   }
 
-  if (serd_stack_is_empty(&writer->anon_stack) || writer->indent == 0) {
-    return serd_world_errorf(
-      writer->world, SERD_ERR_UNKNOWN, "unexpected end of anonymous node\n");
+  if (serd_stack_is_empty(&writer->anon_stack)) {
+    return serd_world_errorf(writer->world,
+                             SERD_ERR_UNKNOWN,
+                             "unexpected end of anonymous node `%s'\n",
+                             serd_node_string(node));
   }
 
-  --writer->indent;
   write_sep(writer, SEP_ANON_END);
-  free_context(writer);
-  writer->context = *anon_stack_top(writer);
-  serd_stack_pop(&writer->anon_stack, sizeof(WriteContext));
+  pop_context(writer);
 
-  const bool is_subject = serd_node_equals(node, writer->context.subject);
-  if (is_subject) {
-    serd_node_set(&writer->context.subject, node);
+  if (serd_node_equals(node, writer->context.subject)) {
+    // Now-finished anonymous node is the new subject with no other context
     memset(writer->context.predicate, 0, sizeof(SerdNode));
   }
 
@@ -961,9 +1047,16 @@ serd_writer_finish(SerdWriter* writer)
   if (ctx(writer, SERD_SUBJECT)) {
     write_sep(writer, SEP_END_S);
   }
+
   if (ctx(writer, SERD_GRAPH)) {
     write_sep(writer, SEP_GRAPH_END);
   }
+
+  // Free any lingering contexts in case there was an error
+  while (!serd_stack_is_empty(&writer->anon_stack)) {
+    pop_context(writer);
+  }
+
   free_context(writer);
   writer->indent  = 0;
   writer->context = WRITE_CONTEXT_NULL;
@@ -991,7 +1084,6 @@ serd_writer_new(SerdWorld*      world,
   writer->write_func = write_func;
   writer->stream     = stream;
   writer->context    = context;
-  writer->list_subj  = NULL;
   writer->empty      = true;
 
   writer->iface.handle   = writer;
diff --git a/test/good/base.ttl b/test/good/base.ttl
index 4c437937..755c1d09 100644
--- a/test/good/base.ttl
+++ b/test/good/base.ttl
@@ -1,3 +1,2 @@
 <foo>
 	a <Bar> .
-
diff --git a/test/good/pretty.trig b/test/good/pretty.trig
new file mode 100644
index 00000000..140769ce
--- /dev/null
+++ b/test/good/pretty.trig
@@ -0,0 +1,98 @@
+@prefix : <http://example.org/> .
+@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
+
+:a
+	:b :c ,
+		:d ,
+		:e ;
+	:f :g ,
+		:h .
+
+(
+	1
+)
+	:isA :List .
+
+[]
+	:isA :Blank .
+
+(
+	2
+)
+	:sameAs (
+		2
+	) .
+
+[]
+	:sameAs [] .
+
+(
+	1
+	2
+)
+	a :List ;
+	rdf:value 3 .
+
+(
+	(
+		3
+	)
+	(
+		4
+	)
+)
+	a :NestedList ;
+	:sum 7 .
+
+[
+	a :BlankSubject
+]
+	a rdf:Resource .
+
+[
+	a :BlankSubject
+] .
+
+[]
+	:blank [
+		:nestedEmptyBlank [] ;
+		:nestedNonEmptyBlanks [
+			rdf:value 1
+		] , [
+			rdf:value 2
+		]
+	] ;
+	:lists (
+		3
+		4
+	) , (
+		5
+		6
+	) , (
+		[
+			rdf:value 7
+		]
+		[
+			rdf:value 8
+		]
+	) .
+
+:s
+	a :Thing ;
+	:predicate1 :object1 ,
+	[
+		a :SubThing ;
+		:predicate2 :object2
+	] , [
+		a :OtherSubThing ;
+		:p3 :o3
+	] ;
+	:p4 :o4 .
+
+eg:graph {
+	:a
+		:b :c ;
+		:d [
+			:e :f
+		] .
+}
diff --git a/test/good/qualify-out.ttl b/test/good/qualify-out.ttl
index 97f67a53..42e4091a 100644
--- a/test/good/qualify-out.ttl
+++ b/test/good/qualify-out.ttl
@@ -2,4 +2,3 @@
 
 eg:s
 	eg:p eg:o .
-