CE implement a pratt parser

ce/ce.c

@@ -14,22 +14,176 @@
 #include <system.h>
 #include <terminal_cursor.h>
 
+static struct arena arena;
+
 #define LINE_BUFFER_MAX 1024
 #define TOKEN_MAX       64
+#define CMD_ARGS_MAX    64
 #define PROMPT          "ce $ "
 
+#define TOKEN_CLASS_OPAREN    0
+#define TOKEN_CLASS_CPAREN    1
+#define TOKEN_CLASS_WORD      2
+#define TOKEN_CLASS_SEMICOLON 3
+
 struct token {
   struct list_node_link tokens_link;
   char buffer[TOKEN_MAX];
+  int class;
 };
 
+#define PREC_NONE   0
+#define PREC_SEQ    1
+#define PREC_LOWEST 2
+
+#define AST_NODE_CLASS_CMD      0
+#define AST_NODE_CLASS_SUBSHELL 1
+#define AST_NODE_CLASS_SEQ      2
+
+struct ast_node;
+
+struct ast_cmd {
+  char* name;
+  char* args[CMD_ARGS_MAX];
+  int arg_count;
+};
+
+struct ast_subshell {
+  struct ast_node* inner;
+};
+
+struct ast_seq {
+  struct ast_node* left;
+  struct ast_node* right;
+};
+
+struct ast_node {
+  int class;
+  union {
+    struct ast_cmd cmd;
+    struct ast_subshell subshell;
+    struct ast_seq seq;
+  } u;
+};
+
+struct parser;
+
+typedef struct ast_node* (*nud_func_t) (struct parser* parser, struct token* token);
+typedef struct ast_node* (*led_func_t) (struct parser* parser, struct token* token,
+                                        struct ast_node* left);
+
+struct parse_rule {
+  nud_func_t nud;
+  led_func_t led;
+  int precedence;
+};
+
+struct parser {
+  struct token* current;
+  struct token* next;
+};
+
+static struct ast_node* word_nud (struct parser* parser, struct token* token);
+
+static struct ast_node* oparen_nud (struct parser* parser, struct token* token);
+
+static struct ast_node* semicolon_led (struct parser* parser, struct token* token,
+                                       struct ast_node* left);
+
+static struct parse_rule parse_rules[] = {
+    [TOKEN_CLASS_WORD] = {&word_nud, NULL, PREC_NONE},
+    [TOKEN_CLASS_OPAREN] = {&oparen_nud, NULL, PREC_NONE},
+    [TOKEN_CLASS_CPAREN] = {NULL, NULL, PREC_NONE},
+    [TOKEN_CLASS_SEMICOLON] = {NULL, &semicolon_led, PREC_SEQ},
+};
+
+static struct token* get_token (struct list_node_link* link) {
+  if (link == NULL)
+    return NULL;
+
+  return list_entry (link, struct token, tokens_link);
+}
+
+static struct token* advance (struct parser* parser) {
+  struct token* token = parser->next;
+
+  if (token != NULL) {
+    parser->current = token;
+    parser->next = get_token (token->tokens_link.next);
+  } else {
+    parser->current = NULL;
+  }
+
+  return token;
+}
+
+static struct ast_node* parse_precedence (struct parser* parser, int precedence) {
+  struct token* token = advance (parser);
+
+  if (token == NULL)
+    return NULL;
+
+  nud_func_t nud = parse_rules[token->class].nud;
+
+  if (nud == NULL)
+    return NULL;
+
+  struct ast_node* left = nud (parser, token);
+
+  while (parser->next && precedence < parse_rules[parser->next->class].precedence) {
+    token = advance (parser);
+    led_func_t led = parse_rules[token->class].led;
+
+    if (led != NULL)
+      left = led (parser, token, left);
+  }
+
+  return left;
+}
+
+static struct ast_node* word_nud (struct parser* parser, struct token* token) {
+  struct ast_node* node = arena_malloc (&arena, sizeof (*node));
+  node->class = AST_NODE_CLASS_CMD;
+  node->u.cmd.name = token->buffer;
+  node->u.cmd.arg_count = 0;
+
+  while (parser->next != NULL && parser->next->class == TOKEN_CLASS_WORD) {
+    struct token* arg = advance (parser);
+
+    if (node->u.cmd.arg_count < CMD_ARGS_MAX)
+      node->u.cmd.args[node->u.cmd.arg_count++] = arg->buffer;
+  }
+
+  return node;
+}
+
+static struct ast_node* oparen_nud (struct parser* parser, struct token* token) {
+  struct ast_node* node = arena_malloc (&arena, sizeof (*node));
+  node->class = AST_NODE_CLASS_SUBSHELL;
+
+  node->u.subshell.inner = parse_precedence (parser, PREC_LOWEST);
+
+  if (parser->next != NULL && parser->next->class == TOKEN_CLASS_CPAREN)
+    advance (parser);
+
+  return node;
+}
+
+static struct ast_node* semicolon_led (struct parser* parser, struct token* token,
+                                       struct ast_node* left) {
+  struct ast_node* node = arena_malloc (&arena, sizeof (*node));
+  node->class = AST_NODE_CLASS_SEQ;
+  node->u.seq.left = left;
+  node->u.seq.right = parse_precedence (parser, PREC_SEQ);
+
+  return node;
+}
+
 static int e_pid;
 static int e_pgid;
 
 static bool run = true;
 
-static struct arena arena;
-
 static void putch (char ch) { mail_send (e_pgid, &ch, 1); }
 void putchar_ (char ch) { putch (ch); }
 
@@ -38,9 +192,6 @@ static bool tokenize_line (void* ctx, const char* start, size_t len) {
 
   struct token* token = arena_malloc (&arena, sizeof (*token));
 
-  if (token == NULL)
-    return false;
-
   memset (token, 0, sizeof (*token));
   memcpy (token->buffer, start, min (sizeof (token->buffer) - 1, len));
 
@@ -49,32 +200,55 @@ static bool tokenize_line (void* ctx, const char* start, size_t len) {
   return true;
 }
 
-static void cmd_echo (struct list_node_link* tokens) {
+static void classify_tokens (struct list_node_link* tokens) {
   struct list_node_link *token_link, *token_tmp_link;
   list_foreach (tokens, token_link, token_tmp_link) {
     struct token* token = list_entry (token_link, struct token, tokens_link);
 
-    printf ("%s ", token->buffer);
+    if (strcmp (token->buffer, "(") == 0) {
+      token->class = TOKEN_CLASS_OPAREN;
+    } else if (strcmp (token->buffer, ")") == 0) {
+      token->class = TOKEN_CLASS_CPAREN;
+    } else if (strcmp (token->buffer, ";") == 0) {
+      token->class = TOKEN_CLASS_SEMICOLON;
+    } else {
+      token->class = TOKEN_CLASS_WORD;
+    }
   }
 }
 
-static void cmd_cat (struct list_node_link* tokens) {
-  if (tokens == NULL) {
-    printf ("ERROR: no file paths provided\n");
-    return;
-  }
+static void execute (struct ast_node* root);
 
+static void parse_tokens (struct list_node_link* tokens) {
+  struct parser parser;
+  parser.current = NULL;
+  parser.next = get_token (tokens);
+
+  while (parser.next != NULL) {
+    struct ast_node* root = parse_precedence (&parser, PREC_LOWEST);
+
+    if (root != NULL) {
+      execute (root);
+    }
+  }
+}
+
+static void echo (char** strings, size_t strings_count) {
+  for (size_t i = 0; i < strings_count; i++)
+    printf ("%s\n", strings[i]);
+}
+
+static void cat (char** file_paths, size_t files_count) {
   struct desc desc;
   char volume[VOLUME_MAX];
   const char* path;
   int ret;
 
-  struct list_node_link *token_link, *token_tmp_link;
-  list_foreach (tokens, token_link, token_tmp_link) {
-    struct token* token = list_entry (token_link, struct token, tokens_link);
+  for (size_t i = 0; i < files_count; i++) {
+    const char* file_path = file_paths[i];
 
-    if (!path_parse (token->buffer, volume, &path)) {
-      printf ("ERROR bad path '%s'\n", token->buffer);
+    if (!path_parse (file_path, volume, &path)) {
+      printf ("ERROR bad path '%s'\n", file_path);
       continue;
     }
 
@@ -104,21 +278,15 @@ static void cmd_cat (struct list_node_link* tokens) {
   }
 }
 
-static void cmd_ls (struct list_node_link* tokens) {
-  if (tokens == NULL) {
-    printf ("ERROR no directory path provided\n");
-    return;
-  }
-
-  struct token* token = list_entry (tokens, struct token, tokens_link);
+static void ls (const char* path_string) {
   struct desc desc;
   char volume[VOLUME_MAX];
   const char* path;
   int ret;
   struct dir_entry entry;
 
-  if (!path_parse (token->buffer, volume, &path)) {
-    printf ("ERROR bad path '%s'\n", token->buffer);
+  if (!path_parse (path_string, volume, &path)) {
+    printf ("ERROR bad path '%s'\n", path_string);
     return;
   }
 
@@ -144,12 +312,12 @@ static void cmd_ls (struct list_node_link* tokens) {
   volume_close ();
 }
 
-static void cmd_quit (void) {
+static void quit1 (void) {
   run = false;
   printf ("Goodbye!\n");
 }
 
-static void cmd_help (void) {
+static void help (void) {
   printf ("Available commands:\n");
   printf ("echo <word1> <word2> <word3> ...\n");
   printf ("help\n");
@@ -158,21 +326,34 @@ static void cmd_help (void) {
   printf ("quit\n");
 }
 
-static void exec_tokens (struct list_node_link* tokens) {
-  struct token* cmd_token = list_entry (tokens, struct token, tokens_link);
-
-  if (strcmp (cmd_token->buffer, "echo") == 0) {
-    cmd_echo (tokens->next);
-  } else if (strcmp (cmd_token->buffer, "help") == 0) {
-    cmd_help ();
-  } else if (strcmp (cmd_token->buffer, "cat") == 0) {
-    cmd_cat (tokens->next);
-  } else if (strcmp (cmd_token->buffer, "ls") == 0) {
-    cmd_ls (tokens->next);
-  } else if (strcmp (cmd_token->buffer, "quit") == 0) {
-    cmd_quit ();
+static void execute_cmd (struct ast_cmd* cmd) {
+  if (strcmp (cmd->name, "echo") == 0) {
+    echo (cmd->args, cmd->arg_count);
+  } else if (strcmp (cmd->name, "help") == 0) {
+    help ();
+  } else if (strcmp (cmd->name, "cat") == 0) {
+    cat (cmd->args, cmd->arg_count);
+  } else if (strcmp (cmd->name, "ls") == 0) {
+    ls (cmd->args[0]);
+  } else if (strcmp (cmd->name, "quit") == 0) {
+    quit1 ();
   } else {
-    printf ("ERROR: unknown command '%s'\n", cmd_token->buffer);
+    printf ("ERROR unknown command '%s'\n", cmd->name);
+  }
+}
+
+static void execute (struct ast_node* root) {
+  switch (root->class) {
+  case AST_NODE_CLASS_CMD:
+    execute_cmd (&root->u.cmd);
+    break;
+  case AST_NODE_CLASS_SUBSHELL:
+    execute (root->u.subshell.inner);
+    break;
+  case AST_NODE_CLASS_SEQ:
+    execute (root->u.seq.left);
+    execute (root->u.seq.right);
+    break;
   }
 }
 
@@ -181,8 +362,10 @@ static void exec_line (const char* line) {
 
   strtokenize (line, ' ', &tokens, &tokenize_line);
 
-  if (tokens != NULL)
-    exec_tokens (tokens);
+  if (tokens != NULL) {
+    classify_tokens (tokens);
+    parse_tokens (tokens);
+  }
 
   arena_reset (&arena);
 }