argument parsing and subcommands

1 files changed, 1416 insertions, 0 deletions

diff --git a/snag/libargs/args.c b/snag/libargs/args.c
new file mode 100644
index 0000000..b004525
--- /dev/null
+++ b/snag/libargs/args.c
@@ -0,0 +1,1416 @@
+#include <stdbool.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <limits.h>
+#include <errno.h>
+#include <ctype.h>
+#include <stdarg.h>
+#include <stdint.h>
+#include <assert.h>
+#include "args.h"
+
+
+/* ------------------ */
+/* Utility functions. */
+/* ------------------ */
+
+
+// Prints a message to stderr and exits with a non-zero status code.
+static void exit_with_error(const char* format_string, ...) {
+    fprintf(stderr, "error: ");
+
+    va_list args;
+    va_start(args, format_string);
+    vfprintf(stderr, format_string, args);
+    va_end(args);
+
+    fprintf(stderr, "\n");
+    exit(1);
+}
+
+
+// Prints to an automatically-allocated string. Returns NULL if an encoding
+// error occurs or if sufficient memory cannot be allocated.
+static char* str(const char* format_string, ...) {
+    va_list args;
+
+    va_start(args, format_string);
+    int len = vsnprintf(NULL, 0, format_string, args);
+    if (len < 0) {
+        return NULL;
+    }
+    va_end(args);
+
+    char *string = malloc(len + 1);
+    if (string == NULL) {
+        return NULL;
+    }
+
+    va_start(args, format_string);
+    vsnprintf(string, len + 1, format_string, args);
+    va_end(args);
+
+    return string;
+}
+
+
+// Duplicates a string, automatically allocating memory for the copy.
+// Returns NULL if memory cannot be allocated for the copy.
+static char* str_dup(const char* string) {
+    size_t len = strlen(string) + 1;
+    char *copy = malloc(len);
+    return copy ? memcpy(copy, string, len) : NULL;
+}
+
+
+// Hashes a string using the FNV-1a algorithm.
+static uint32_t str_hash(const char* string) {
+    uint32_t hash = 2166136261u;
+    size_t length = strlen(string);
+    for (size_t i = 0; i < length; i++) {
+        hash ^= (uint8_t)string[i];
+        hash *= 16777619;
+    }
+    return hash;
+}
+
+
+// Attempts to parse a string as an integer value, exiting on failure.
+static int try_str_to_int(const char* string) {
+    char *endptr;
+    errno = 0;
+    long result = strtol(string, &endptr, 0);
+    if (errno == ERANGE || result > INT_MAX || result < INT_MIN) {
+        exit_with_error("'%s' is out of range", string);
+    }
+    if (*endptr != '\0') {
+        exit_with_error("cannot parse '%s' as an integer", string);
+    }
+    return (int) result;
+}
+
+
+// Attempts to parse a string as a double value, exiting on failure.
+static double try_str_to_double(const char* string) {
+    char *endptr;
+    errno = 0;
+    double result = strtod(string, &endptr);
+    if (errno == ERANGE) {
+        exit_with_error("'%s' is out of range", string);
+    }
+    if (*endptr != '\0') {
+        exit_with_error("cannot parse '%s' as a floating-point value", string);
+    }
+    return result;
+}
+
+
+/* --------------------------------- */
+/* Vec: a dynamic array of pointers. */
+/* --------------------------------- */
+
+
+typedef struct {
+    int count;
+    int capacity;
+    void** entries;
+} Vec;
+
+
+static Vec* vec_new(void) {
+    Vec* vec = malloc(sizeof(Vec));
+    if (!vec) {
+        return NULL;
+    }
+    vec->count = 0;
+    vec->capacity = 0;
+    vec->entries = NULL;
+    return vec;
+}
+
+
+static void vec_free(Vec* vec) {
+    if (vec) {
+        free(vec->entries);
+        free(vec);
+    }
+}
+
+
+static bool vec_add(Vec* vec, void* entry) {
+    if (vec->count + 1 > vec->capacity) {
+        int new_capacity = vec->capacity < 8 ? 8 : vec->capacity * 2;
+        void** new_array = realloc(vec->entries, sizeof(void*) * new_capacity);
+        if (!new_array) {
+            return false;
+        }
+        vec->entries = new_array;
+        vec->capacity = new_capacity;
+    }
+    vec->entries[vec->count] = entry;
+    vec->count++;
+    return true;
+}
+
+
+/* ------------------------------------------------------------------- */
+/* Map: a linear-probing hash map with string-keys and pointer-values. */
+/* ------------------------------------------------------------------- */
+
+
+// The map automatically grows to keep count/capacity < MAP_MAX_LOAD.
+// This data structure performs optimally when it's less than half-full.
+#define MAP_MAX_LOAD 0.5
+
+
+typedef struct {
+    char* key;
+    void* value;
+    uint32_t key_hash;
+} MapEntry;
+
+
+typedef struct {
+    int count;
+    int capacity;
+    int max_load_threshold;
+    MapEntry* entries;
+} Map;
+
+
+static Map* map_new(void) {
+    Map* map = malloc(sizeof(Map));
+    if (!map) {
+        return NULL;
+    }
+    map->count = 0;
+    map->capacity = 0;
+    map->max_load_threshold = 0;
+    map->entries = NULL;
+    return map;
+}
+
+
+static void map_free(Map* map) {
+    if (map) {
+        for (int i = 0; i < map->capacity; i++) {
+            MapEntry* entry = &map->entries[i];
+            if (entry->key != NULL) {
+                free(entry->key);
+            }
+        }
+        free(map->entries);
+        free(map);
+    }
+}
+
+
+static MapEntry* map_find(Map* map, const char* key, uint32_t key_hash) {
+    // Capacity is always a power of 2 so we can use bitwise-AND as a fast
+    // modulo operator, i.e. this is equivalent to: index = key_hash % capacity.
+    size_t index = key_hash & (map->capacity - 1);
+
+    for (;;) {
+        MapEntry* entry = &map->entries[index];
+        if (entry->key == NULL) {
+            return entry;
+        } else if (key_hash == entry->key_hash && strcmp(key, entry->key) == 0) {
+            return entry;
+        }
+        index = (index + 1) & (map->capacity - 1);
+    }
+}
+
+
+static bool map_grow(Map* map) {
+    MapEntry* old_entries = map->entries;
+    int old_capacity = map->capacity;
+    int new_capacity = old_capacity < 8 ? 8 : old_capacity * 2;
+
+    MapEntry* new_entries = malloc(sizeof(MapEntry) * new_capacity);
+    if (!new_entries) {
+        return false;
+    }
+
+    for (int i = 0; i < new_capacity; i++) {
+        new_entries[i].key = NULL;
+    }
+
+    map->count = 0;
+    map->capacity = new_capacity;
+    map->max_load_threshold = new_capacity * MAP_MAX_LOAD;
+    map->entries = new_entries;
+
+    for (int i = 0; i < old_capacity; i++) {
+        MapEntry* src = &old_entries[i];
+        if (src->key == NULL) continue;
+
+        MapEntry* dst = map_find(map, src->key, src->key_hash);
+        dst->key = src->key;
+        dst->value = src->value;
+        dst->key_hash = src->key_hash;
+        map->count++;
+    }
+
+    free(old_entries);
+    return true;
+}
+
+
+// Returns true if the key was found.
+static bool map_get(Map* map, const char* key, void** value) {
+    if (map->count == 0) return false;
+
+    uint32_t key_hash = str_hash(key);
+    MapEntry* entry = map_find(map, key, key_hash);
+    if (entry->key == NULL) return false;
+
+    *value = entry->value;
+    return true;
+}
+
+
+// Adds a new entry to the map or updates the value of an existing entry.
+// (Note that the map stores its own internal copy of the key string.)
+static bool map_set(Map* map, const char* key, void* value) {
+    if (map->count == map->max_load_threshold) {
+        if (!map_grow(map)) {
+            return false;
+        }
+    }
+
+    uint32_t key_hash = str_hash(key);
+    MapEntry* entry = map_find(map, key, key_hash);
+    if (entry->key == NULL) {
+        char* key_copy = str_dup(key);
+        if (!key_copy) {
+            return false;
+        }
+        map->count++;
+        entry->key = key_copy;
+        entry->value = value;
+        entry->key_hash = key_hash;
+    } else {
+        entry->value = value;
+    }
+
+    return true;
+}
+
+
+// Convenience wrapper for map_set(). This splits the key string into space-
+// separated words and adds a separate entry to the map for each word.
+static bool map_set_splitkey(Map* map, const char* key_string, void* value) {
+    char *copy_of_key_string = str_dup(key_string);
+    if (!copy_of_key_string) {
+        return false;
+    }
+
+    char* word_start = copy_of_key_string;
+    char* string_end = word_start + strlen(copy_of_key_string);
+
+    while (word_start < string_end) {
+        if (*word_start == ' ') {
+            word_start++;
+            continue;
+        }
+
+        char* word_end = word_start;
+        while (true) {
+            if (*word_end == ' ' || *word_end == '\0') {
+                break;
+            }
+            word_end++;
+        }
+        *word_end = '\0';
+
+        if (!map_set(map, word_start, value)) {
+            free(copy_of_key_string);
+            return false;
+        }
+
+        word_start = word_end + 1;
+    }
+
+    free(copy_of_key_string);
+    return true;
+}
+
+
+/* -------- */
+/* Options. */
+/* -------- */
+
+
+typedef enum {
+    OPT_FLAG,
+    OPT_STR,
+    OPT_INT,
+    OPT_DBL,
+} OptionType;
+
+
+typedef union {
+    char* str_val;
+    int int_val;
+    double dbl_val;
+} OptionValue;
+
+
+typedef struct {
+    OptionType type;
+    int count;
+    int capacity;
+    OptionValue* values;
+    OptionValue fallback;
+    bool is_greedy;
+} Option;
+
+
+static void option_free(Option* opt) {
+    if (opt) {
+        free(opt->values);
+        free(opt);
+    }
+}
+
+
+static bool option_append_value(Option* opt, OptionValue value) {
+    if (opt->count + 1 > opt->capacity) {
+        int new_capacity = opt->capacity < 4 ? 4 : opt->capacity * 2;
+        OptionValue* new_array = realloc(opt->values, sizeof(OptionValue) * new_capacity);
+        if (!new_array) {
+            return false;
+        }
+        opt->capacity = new_capacity;
+        opt->values = new_array;
+    }
+    opt->values[opt->count] = value;
+    opt->count++;
+    return true;
+}
+
+
+static bool option_try_set(Option* opt, char* arg) {
+    if (opt->type == OPT_STR) {
+        return option_append_value(opt, (OptionValue){.str_val = arg});
+    }
+    else if (opt->type == OPT_INT) {
+        int value = try_str_to_int(arg);
+        return option_append_value(opt, (OptionValue){.int_val = value});
+    }
+    else if (opt->type == OPT_DBL) {
+        double value = try_str_to_double(arg);
+        return option_append_value(opt, (OptionValue){.dbl_val = value});
+    }
+    assert(false);
+    return false;
+}
+
+
+static Option* option_new(void) {
+    Option *option = malloc(sizeof(Option));
+    if (!option) {
+        return NULL;
+    }
+    option->count = 0;
+    option->capacity = 0;
+    option->values = NULL;
+    option->is_greedy = false;
+    return option;
+}
+
+
+static Option* option_new_flag(void) {
+    Option *opt = option_new();
+    if (!opt) {
+        return NULL;
+    }
+    opt->type = OPT_FLAG;
+    return opt;
+}
+
+
+static Option* option_new_str(char* fallback) {
+    Option *opt = option_new();
+    if (!opt) {
+        return NULL;
+    }
+    opt->type = OPT_STR;
+    opt->fallback = (OptionValue){.str_val = fallback};
+    return opt;
+}
+
+
+static Option* option_new_int(int fallback) {
+    Option *opt = option_new();
+    if (!opt) {
+        return NULL;
+    }
+    opt->type = OPT_INT;
+    opt->fallback = (OptionValue){.int_val = fallback};
+    return opt;
+}
+
+
+static Option* option_new_double(double fallback) {
+    Option *opt = option_new();
+    if (!opt) {
+        return NULL;
+    }
+    opt->type = OPT_DBL;
+    opt->fallback = (OptionValue){.dbl_val = fallback};
+    return opt;
+}
+
+
+static char* option_get_str(Option* opt) {
+    if (opt->count > 0) {
+        return opt->values[opt->count - 1].str_val;
+    }
+    return opt->fallback.str_val;
+}
+
+
+static int option_get_int(Option* opt) {
+    if (opt->count > 0) {
+        return opt->values[opt->count - 1].int_val;
+    }
+    return opt->fallback.int_val;
+}
+
+
+static double option_get_double(Option* opt) {
+    if (opt->count > 0) {
+        return opt->values[opt->count - 1].dbl_val;
+    }
+    return opt->fallback.dbl_val;
+}
+
+
+// Returns the option's values as a freshly-allocated array of string pointers.
+static char** option_get_str_list(Option* opt) {
+    if (opt->count == 0) {
+        return NULL;
+    }
+    char** list = malloc(sizeof(char*) * opt->count);
+    if (!list) {
+        return NULL;
+    }
+    for (int i = 0; i < opt->count; i++) {
+        list[i] = opt->values[i].str_val;
+    }
+    return list;
+}
+
+
+// Returns the option's values as a freshly-allocated array of integers.
+static int* option_get_int_list(Option* opt) {
+    if (opt->count == 0) {
+        return NULL;
+    }
+    int* list = malloc(sizeof(int) * opt->count );
+    if (!list) {
+        return NULL;
+    }
+    for (int i = 0; i < opt->count ; i++) {
+        list[i] = opt->values[i].int_val;
+    }
+    return list;
+}
+
+
+// Returns the option's values as a freshly-allocated array of doubles.
+static double* option_get_double_list(Option* opt) {
+    if (opt->count  == 0) {
+        return NULL;
+    }
+    double* list = malloc(sizeof(double) * opt->count );
+    if (!list) {
+        return NULL;
+    }
+    for (int i = 0; i < opt->count ; i++) {
+        list[i] = opt->values[i].dbl_val;
+    }
+    return list;
+}
+
+
+// Returns a freshly-allocated state-string for debugging.
+static char* option_to_str(Option* opt) {
+    if (opt->type == OPT_FLAG) {
+        return str("%i", opt->count);
+    }
+
+    char *fallback = NULL;
+    if (opt->type == OPT_STR) {
+        fallback = str_dup(opt->fallback.str_val);
+    } else if (opt->type == OPT_INT) {
+        fallback = str("%i", opt->fallback.int_val);
+    } else if (opt->type == OPT_DBL) {
+        fallback = str("%f", opt->fallback.dbl_val);
+    }
+
+    char *values = str_dup("");
+    for (int i = 0; i < opt->count; i++) {
+        char *value = NULL;
+        if (opt->type == OPT_STR) {
+            value = str_dup(opt->values[i].str_val);
+        } else if (opt->type == OPT_INT) {
+            value = str("%i", opt->values[i].int_val);
+        } else if (opt->type == OPT_DBL) {
+            value = str("%f", opt->values[i].dbl_val);
+        }
+        char *old_values = values;
+        if (i == 0) {
+            values = str_dup(value);
+        } else {
+            values = str("%s, %s", old_values, value);
+        }
+        free(old_values);
+        free(value);
+    }
+
+    char *output = str("(%s) [%s]", fallback, values);
+    free(fallback);
+    free(values);
+    return output;
+}
+
+
+/* ----------------------------------------------------- */
+/* ArgStream: a wrapper for an array of string pointers. */
+/* ----------------------------------------------------- */
+
+
+typedef struct ArgStream {
+    int count;
+    int index;
+    char** args;
+} ArgStream;
+
+
+static ArgStream* argstream_new(int count, char** args) {
+    ArgStream* stream = malloc(sizeof(ArgStream));
+    if (!stream) {
+        return NULL;
+    }
+    stream->count = count;
+    stream->index = 0;
+    stream->args = args;
+    return stream;
+}
+
+
+static void argstream_free(ArgStream* stream) {
+    free(stream);
+}
+
+
+static char* argstream_next(ArgStream* stream) {
+    return stream->args[stream->index++];
+}
+
+
+static bool argstream_has_next(ArgStream* stream) {
+    return stream->index < stream->count;
+}
+
+
+/* ----------------- */
+/* ArgParser: setup. */
+/* ----------------- */
+
+
+struct ArgParser {
+    char* helptext;
+    char* version;
+    Vec* option_vec;
+    Map* option_map;
+    Vec* command_vec;
+    Map* command_map;
+    Vec* positional_args;
+    ap_callback_t cmd_callback;
+    int cmd_callback_exit_code;
+    char* cmd_name;
+    struct ArgParser* cmd_parser;
+    struct ArgParser* root_parser;
+    bool enable_help_command;
+    bool had_memory_error;
+    struct ArgParser* parent;
+    bool first_pos_arg_ends_option_parsing;
+    bool all_args_as_pos_args;
+    char* zeroth_root_arg;
+};
+
+
+ArgParser* ap_new_parser(void) {
+    ArgParser *parser = malloc(sizeof(ArgParser));
+    if (!parser) {
+        return NULL;
+    }
+
+    parser->helptext = NULL;
+    parser->version = NULL;
+    parser->cmd_callback = NULL;
+    parser->cmd_callback_exit_code = 0;
+    parser->cmd_name = NULL;
+    parser->cmd_parser = NULL;
+    parser->enable_help_command = false;
+    parser->had_memory_error = false;
+    parser->parent = NULL;
+    parser->first_pos_arg_ends_option_parsing = false;
+    parser->all_args_as_pos_args = false;
+    parser->option_vec = NULL;
+    parser->option_map = NULL;
+    parser->command_vec = NULL;
+    parser->command_map = NULL;
+    parser->positional_args = NULL;
+    parser->root_parser = parser;
+    parser->zeroth_root_arg = NULL;
+
+    parser->option_vec = vec_new();
+    if (!parser->option_vec) {
+        ap_free(parser);
+        return NULL;
+    }
+
+    parser->option_map = map_new();
+    if (!parser->option_map) {
+        ap_free(parser);
+        return NULL;
+    }
+
+    parser->command_vec = vec_new();
+    if (!parser->command_vec) {
+        ap_free(parser);
+        return NULL;
+    }
+
+    parser->command_map = map_new();
+    if (!parser->command_map) {
+        ap_free(parser);
+        return NULL;
+    }
+
+    parser->positional_args = vec_new();
+    if (!parser->positional_args) {
+        ap_free(parser);
+        return NULL;
+    }
+
+    return parser;
+}
+
+
+void ap_free(ArgParser* parser) {
+    if (!parser) {
+        return;
+    }
+
+    free(parser->helptext);
+    free(parser->version);
+
+    if (parser->option_map) {
+        map_free(parser->option_map);
+    }
+
+    if (parser->option_vec) {
+        for (int i = 0; i < parser->option_vec->count; i++) {
+            option_free(parser->option_vec->entries[i]);
+        }
+        vec_free(parser->option_vec);
+    }
+
+    if (parser->command_map) {
+        map_free(parser->command_map);
+    }
+
+    if (parser->command_vec) {
+        for (int i = 0; i < parser->command_vec->count; i++) {
+            ap_free(parser->command_vec->entries[i]);
+        }
+        vec_free(parser->command_vec);
+    }
+
+    if (parser->positional_args) {
+        vec_free(parser->positional_args);
+    }
+
+    free(parser);
+}
+
+
+static void ap_set_memory_error_flag(ArgParser* parser) {
+    parser->had_memory_error = true;
+
+    ArgParser* parent = parser->parent;
+    while (parent) {
+        parent->had_memory_error = true;
+        parent = parent->parent;
+    }
+}
+
+
+void ap_set_helptext(ArgParser* parser, const char* helptext) {
+    free(parser->helptext);
+    parser->helptext = NULL;
+
+    if (helptext) {
+        parser->helptext = str_dup(helptext);
+        if (!parser->helptext) {
+            ap_set_memory_error_flag(parser);
+        }
+    }
+}
+
+
+char* ap_get_helptext(ArgParser* parser) {
+    return parser->helptext;
+}
+
+
+void ap_set_version(ArgParser* parser, const char* version) {
+    free(parser->version);
+    parser->version = NULL;
+
+    if (version) {
+        parser->version = str_dup(version);
+        if (!parser->version) {
+            ap_set_memory_error_flag(parser);
+        }
+    }
+}
+
+
+char* ap_get_version(ArgParser* parser) {
+    return parser->version;
+}
+
+
+void ap_first_pos_arg_ends_option_parsing(ArgParser* parser) {
+    parser->first_pos_arg_ends_option_parsing = true;
+}
+
+
+void ap_all_args_as_pos_args(ArgParser* parser) {
+    parser->all_args_as_pos_args = true;
+}
+
+
+/* -------------------------------------- */
+/* ArgParser: register flags and options. */
+/* -------------------------------------- */
+
+
+static void ap_register_option(ArgParser* parser, const char* name, Option* opt) {
+    if (!opt) {
+        ap_set_memory_error_flag(parser);
+        return;
+    }
+
+    if (vec_add(parser->option_vec, opt)) {
+        if (map_set_splitkey(parser->option_map, name, opt)) {
+            return;
+        } else {
+            ap_set_memory_error_flag(parser);
+            parser->option_vec->count--;
+            option_free(opt);
+            return;
+        }
+    } else {
+        ap_set_memory_error_flag(parser);
+        option_free(opt);
+        return;
+    }
+}
+
+
+// Register a new flag.
+void ap_add_flag(ArgParser *parser, const char* name) {
+    Option* opt = option_new_flag();
+    ap_register_option(parser, name, opt);
+}
+
+
+// Register a new string-valued option.
+void ap_add_str_opt(ArgParser* parser, const char* name, const char* fallback) {
+    Option* opt = option_new_str((char*)fallback);
+    ap_register_option(parser, name, opt);
+}
+
+
+// Register a new greedy string-valued option.
+void ap_add_greedy_str_opt(ArgParser* parser, const char* name) {
+    Option* opt = option_new_str((char*)"");
+    if (opt) {
+        opt->is_greedy = true;
+    }
+    ap_register_option(parser, name, opt);
+}
+
+
+// Register a new integer-valued option.
+void ap_add_int_opt(ArgParser* parser, const char* name, int fallback) {
+    Option* opt = option_new_int(fallback);
+    ap_register_option(parser, name, opt);
+}
+
+
+// Register a new double-valued option.
+void ap_add_dbl_opt(ArgParser* parser, const char* name, double fallback) {
+    Option* opt = option_new_double(fallback);
+    ap_register_option(parser, name, opt);
+}
+
+
+/* ---------------------------------- */
+/* ArgParser: flag and option values. */
+/* ---------------------------------- */
+
+
+// Retrieve an Option instance by name.
+static Option* ap_get_opt(ArgParser* parser, const char* name) {
+    void* opt;
+    if (!map_get(parser->option_map, name, &opt)) {
+        exit_with_error("'%s' is not a registered flag or option name", name);
+    }
+    return (Option*)opt;
+}
+
+
+// Returns the number of times the specified flag or option was found.
+int ap_count(ArgParser* parser, const char* name) {
+    Option* opt = ap_get_opt(parser, name);
+    return opt->count;
+}
+
+
+// Returns true if the specified flag or option was found.
+bool ap_found(ArgParser* parser, const char* name) {
+    Option* opt = ap_get_opt(parser, name);
+    return opt->count > 0;
+}
+
+
+// Returns the value of the specified string option.
+char* ap_get_str_value(ArgParser* parser, const char* name) {
+    Option* opt = ap_get_opt(parser, name);
+    return (char*)option_get_str(opt);
+}
+
+
+// Returns the string value at the specified index.
+char* ap_get_str_value_at_index(ArgParser* parser, const char* name, int index) {
+    Option* opt = ap_get_opt(parser, name);
+    return opt->values[index].str_val;
+}
+
+
+// Returns the value of the specified integer option.
+int ap_get_int_value(ArgParser* parser, const char* name) {
+    Option* opt = ap_get_opt(parser, name);
+    return option_get_int(opt);
+}
+
+
+// Returns the integer value at the specified index.
+int ap_get_int_value_at_index(ArgParser* parser, const char* name, int index) {
+    Option* opt = ap_get_opt(parser, name);
+    return opt->values[index].int_val;
+}
+
+
+// Returns the value of the specified floating-point option.
+double ap_get_dbl_value(ArgParser* parser, const char* name) {
+    Option* opt = ap_get_opt(parser, name);
+    return option_get_double(opt);
+}
+
+
+// Returns the floating-point value at the specified index.
+double ap_get_dbl_value_at_index(ArgParser* parser, const char* name, int index) {
+    Option* opt = ap_get_opt(parser, name);
+    return opt->values[index].dbl_val;
+}
+
+
+// Returns an option's values as a freshly-allocated array of string pointers.
+// The array's memory is not affected by calls to ap_free().
+// Returns NULL if memory cannot be allocated for the array.
+char** ap_get_str_values(ArgParser* parser, const char* name) {
+    Option* opt = ap_get_opt(parser, name);
+    return (char**)option_get_str_list(opt);
+}
+
+
+// Returns an option's values as a freshly-allocated array of integers. The
+// array's memory is not affected by calls to ap_free().
+// Returns NULL if memory cannot be allocated for the array.
+int* ap_get_int_values(ArgParser* parser, const char* name) {
+    Option* opt = ap_get_opt(parser, name);
+    return option_get_int_list(opt);
+}
+
+
+// Returns an option's values as a freshly-allocated array of doubles. The
+// array's memory is not affected by calls to ap_free().
+// Returns NULL if memory cannot be allocated for the array.
+double* ap_get_dbl_values(ArgParser* parser, const char* name) {
+    Option* opt = ap_get_opt(parser, name);
+    return option_get_double_list(opt);
+}
+
+
+/* -------------------------------- */
+/* ArgParser: positional arguments. */
+/* -------------------------------- */
+
+
+// Returns true if the parser has found one or more positional arguments.
+bool ap_has_args(ArgParser* parser) {
+    return parser->positional_args->count > 0;
+}
+
+
+// Returns the number of positional arguments.
+int ap_count_args(ArgParser* parser) {
+    return parser->positional_args->count;
+}
+
+
+// Returns the positional argument at the specified index.
+char* ap_get_arg_at_index(ArgParser* parser, int index) {
+    return (char*)parser->positional_args->entries[index];
+}
+
+
+// Returns the positional arguments as a freshly-allocated array of string
+// pointers. The memory occupied by the returned array is not affected by
+// calls to ap_free().
+// Returns NULL if memory cannot be allocated for the array.
+char** ap_get_args(ArgParser* parser) {
+    int count = ap_count_args(parser);
+    char** args = malloc(sizeof(char*) * count);
+    if (!args) {
+        return NULL;
+    }
+    memcpy(args, parser->positional_args->entries, sizeof(char*) * count);
+    return args;
+}
+
+
+// Attempts to parse and return the positional arguments as a freshly
+// allocated array of integers. Exits with an error message on failure. The
+// memory occupied by the returned array is not affected by calls to
+// ap_free().
+// Returns NULL if memory cannot be allocated for the array.
+int* ap_get_args_as_ints(ArgParser* parser) {
+    int count = ap_count_args(parser);
+    int* args = malloc(sizeof(int) * count);
+    if (!args) {
+        return NULL;
+    }
+    for (int i = 0; i < count; i++) {
+        *(args + i) = try_str_to_int(parser->positional_args->entries[i]);
+    }
+    return args;
+}
+
+
+// Attempts to parse and return the positional arguments as a freshly
+// allocated array of doubles. Exits with an error message on failure. The
+// memory occupied by the returned array is not affected by calls to
+// ap_free().
+// Returns NULL if memory cannot be allocated for the array.
+double* ap_get_args_as_doubles(ArgParser* parser) {
+    int count = ap_count_args(parser);
+    double *args = malloc(sizeof(double) * count);
+    if (!args) {
+        return NULL;
+    }
+    for (int i = 0; i < count; i++) {
+        *(args + i) = try_str_to_double(parser->positional_args->entries[i]);
+    }
+    return args;
+}
+
+
+/* -------------------- */
+/* ArgParser: commands. */
+/* -------------------- */
+
+
+ArgParser* ap_new_cmd(ArgParser* parent_parser, const char* name) {
+    ArgParser* cmd_parser = ap_new_parser();
+    if (!cmd_parser) {
+        return NULL;
+    }
+
+    cmd_parser->root_parser = parent_parser->root_parser;
+
+    if (vec_add(parent_parser->command_vec, cmd_parser)) {
+        if (map_set_splitkey(parent_parser->command_map, name, cmd_parser)) {
+            parent_parser->enable_help_command = true;
+            return cmd_parser;
+        } else {
+            parent_parser->command_vec--;
+            ap_free(cmd_parser);
+            return NULL;
+        }
+    } else {
+        ap_free(cmd_parser);
+        return NULL;
+    }
+}
+
+
+void ap_set_cmd_callback(ArgParser* cmd_parser, ap_callback_t cmd_callback) {
+    cmd_parser->cmd_callback = cmd_callback;
+}
+
+
+bool ap_found_cmd(ArgParser* parent_parser) {
+    return parent_parser->cmd_name != NULL;
+}
+
+
+char* ap_get_cmd_name(ArgParser* parent_parser) {
+    return parent_parser->cmd_name;
+}
+
+
+ArgParser* ap_get_cmd_parser(ArgParser* parent_parser) {
+    return parent_parser->cmd_parser;
+}
+
+
+int ap_get_cmd_exit_code(ArgParser* parent_parser) {
+    return parent_parser->cmd_callback_exit_code;
+}
+
+
+void ap_enable_help_command(ArgParser* parent_parser, bool enable) {
+    parent_parser->enable_help_command = enable;
+}
+
+
+ArgParser* ap_get_parent(ArgParser* parser) {
+    return parser->parent;
+}
+
+
+/* --------------------------- */
+/* ArgParser: parse arguments. */
+/* --------------------------- */
+
+
+// Parse an option of the form --name=value or -n=value.
+static void ap_handle_equals_opt(ArgParser* parser, const char* prefix, char* arg, ArgStream* stream) {
+    char* array = str_dup(arg);
+    if (!array) {
+        ap_set_memory_error_flag(parser);
+        return;
+    }
+
+    *strchr(array, '=') = '\0';
+    char* name = array;
+    char* value = strchr(arg, '=') + 1;
+
+    Option* option;
+    bool found = map_get(parser->option_map, name, (void**)&option);
+
+    if (!found) {
+        /* free(array); */
+        exit_with_error("%s%s is not a recognised option name", prefix, name);
+    }
+
+    if (option->type == OPT_FLAG) {
+        /* free(array); */
+        exit_with_error("flag %s%s does not accept an argument", prefix, name);
+    }
+
+    if (strlen(value) == 0) {
+        /* free(array); */
+        exit_with_error("missing argument for %s%s", prefix, name);
+    }
+
+    if (!option_try_set(option, value)) {
+        ap_set_memory_error_flag(parser);
+    }
+
+    if (option->is_greedy) {
+        while (argstream_has_next(stream)) {
+            if (!option_try_set(option, argstream_next(stream))) {
+                ap_set_memory_error_flag(parser);
+            }
+        }
+    }
+
+    free(array);
+}
+
+
+// Parse a long-form option, i.e. an option beginning with a double dash.
+static void ap_handle_long_opt(ArgParser* parser, const char* arg, ArgStream* stream) {
+    Option* option;
+
+    if (map_get(parser->option_map, arg, (void**)&option)) {
+        if (option->type == OPT_FLAG) {
+            option->count++;
+            return;
+        }
+
+        if (argstream_has_next(stream) && option->is_greedy) {
+            while (argstream_has_next(stream)) {
+                if (!option_try_set(option, argstream_next(stream))) {
+                    ap_set_memory_error_flag(parser);
+                }
+            }
+            return;
+        }
+
+        if (argstream_has_next(stream)) {
+            if (!option_try_set(option, argstream_next(stream))) {
+                ap_set_memory_error_flag(parser);
+            }
+            return;
+        }
+
+        exit_with_error("missing argument for --%s", arg);
+    }
+
+    if (strcmp(arg, "help") == 0 && parser->helptext != NULL) {
+        puts(parser->helptext);
+        exit(0);
+    }
+
+    if (strcmp(arg, "version") == 0 && parser->version != NULL) {
+        puts(parser->version);
+        exit(0);
+    }
+
+    exit_with_error("--%s is not a recognised flag or option name", arg);
+}
+
+
+// Parse a short-form option, i.e. an option beginning with a single dash.
+static void ap_handle_short_opt(ArgParser* parser, const char* arg, ArgStream* stream) {
+    for (size_t i = 0; i < strlen(arg); i++) {
+        char keystr[] = {arg[i], 0};
+        Option* option;
+
+        bool found = map_get(parser->option_map, keystr, (void**)&option);
+        if (!found) {
+            if (arg[i] == 'h' && parser->helptext != NULL) {
+                puts(parser->helptext);
+                exit(0);
+            }
+            if (arg[i] == 'v' && parser->version != NULL) {
+                puts(parser->version);
+                exit(0);
+            }
+            if (strlen(arg) > 1) {
+                exit_with_error("'%c' in -%s is not a recognised flag or option name", arg[i], arg);
+            }
+            exit_with_error("-%s is not a recognised flag or option name", arg);
+        }
+
+        if (option->type == OPT_FLAG) {
+            option->count++;
+            continue;
+        }
+
+        if (argstream_has_next(stream) && option->is_greedy) {
+            while (argstream_has_next(stream)) {
+                if (!option_try_set(option, argstream_next(stream))) {
+                    ap_set_memory_error_flag(parser);
+                }
+            }
+            continue;
+        }
+
+        if (argstream_has_next(stream)) {
+            if (!option_try_set(option, argstream_next(stream))) {
+                ap_set_memory_error_flag(parser);
+            }
+            continue;
+        }
+
+        if (strlen(arg) > 1) {
+            exit_with_error("missing argument for '%c' in -%s", arg[i], arg);
+        }
+
+        exit_with_error("missing argument for -%s", arg);
+    }
+}
+
+
+// Parse a stream of string arguments.
+static void ap_parse_stream(ArgParser* parser, ArgStream* stream) {
+    if (parser->had_memory_error) {
+        return;
+    }
+
+    if (parser->all_args_as_pos_args) {
+        while (argstream_has_next(stream)) {
+            if (!vec_add(parser->positional_args, argstream_next(stream))) {
+                ap_set_memory_error_flag(parser);
+            }
+        }
+        return;
+    }
+
+    while (argstream_has_next(stream)) {
+        ArgParser* cmd_parser;
+        char* arg = argstream_next(stream);
+
+        // If we encounter a '--' argument, turn off option-parsing.
+        if (strcmp(arg, "--") == 0) {
+            while (argstream_has_next(stream)) {
+                if (!vec_add(parser->positional_args, argstream_next(stream))) {
+                    ap_set_memory_error_flag(parser);
+                }
+            }
+        }
+
+        // Is the argument a long-form option or flag?
+        else if (strncmp(arg, "--", 2) == 0) {
+            if (strstr(arg, "=") != NULL) {
+                ap_handle_equals_opt(parser, "--", arg + 2, stream);
+            } else {
+                ap_handle_long_opt(parser, arg + 2, stream);
+            }
+        }
+
+        // Is the argument a short-form option or flag?
+        else if (arg[0] == '-') {
+            if (strlen(arg) == 1 || isdigit(arg[1])) {
+                if (!vec_add(parser->positional_args, arg)) {
+                    ap_set_memory_error_flag(parser);
+                }
+            } else if (strstr(arg, "=") != NULL) {
+                ap_handle_equals_opt(parser, "-", arg + 1, stream);
+            } else {
+                ap_handle_short_opt(parser, arg + 1, stream);
+            }
+        }
+
+        // Is the argument a registered command?
+        else if (parser->positional_args->count == 0 && map_get(parser->command_map, arg, (void**)&cmd_parser)) {
+            parser->cmd_name = arg;
+            parser->cmd_parser = cmd_parser;
+            ap_parse_stream(cmd_parser, stream);
+            if (cmd_parser->cmd_callback && !parser->had_memory_error) {
+                parser->cmd_callback_exit_code = cmd_parser->cmd_callback(arg, cmd_parser);
+            }
+        }
+
+        // Is the argument the automatic 'help' command?
+        else if (parser->positional_args->count == 0 && parser->enable_help_command && strcmp(arg, "help") == 0) {
+            if (argstream_has_next(stream)) {
+                char* name = argstream_next(stream);
+                if (map_get(parser->command_map, name, (void**)&cmd_parser)) {
+                    if (cmd_parser->helptext) {
+                        puts(cmd_parser->helptext);
+                    }
+                    exit(0);
+                } else {
+                    exit_with_error("'%s' is not a recognised command", name);
+                }
+            } else {
+                exit_with_error("the 'help' command requires an argument");
+            }
+        }
+
+        // Otherwise add the argument to our list of positionals.
+        else {
+            if (!vec_add(parser->positional_args, arg)) {
+                ap_set_memory_error_flag(parser);
+            }
+            if (parser->first_pos_arg_ends_option_parsing) {
+                while (argstream_has_next(stream)) {
+                    if (!vec_add(parser->positional_args, argstream_next(stream))) {
+                        ap_set_memory_error_flag(parser);
+                    }
+                }
+            }
+        }
+    }
+}
+
+
+// Parse an array of string arguments. We assume that [argc] and [argv] are the arguments passed to
+// main(), i.e. we ignore the first element in the array. In some situations [argv] can be empty,
+// i.e. [argc == 0], which can lead to security vulnerabilities if not explicitly handled.
+bool ap_parse(ArgParser* parser, int argc, char** argv) {
+    if (parser->had_memory_error) {
+        return false;
+    }
+
+    if (argc == 0) {
+        return true;
+    }
+
+    parser->zeroth_root_arg = argv[0];
+
+    ArgStream* stream = argstream_new(argc - 1 , argv + 1);
+    if (!stream) {
+        return false;
+    }
+
+    ap_parse_stream(parser, stream);
+    argstream_free(stream);
+
+    return !parser->had_memory_error;
+}
+
+
+/* --------------------- */
+/* ArgParser: utilities. */
+/* --------------------- */
+
+
+bool ap_had_memory_error(ArgParser* parser) {
+    return parser->had_memory_error;
+}
+
+
+void ap_print(ArgParser* parser) {
+    puts("Flags/Options:");
+    if (parser->option_map->count > 0) {
+        for (int i = 0; i < parser->option_map->capacity; i++) {
+            MapEntry* entry = &parser->option_map->entries[i];
+            if (entry->key != NULL) {
+                Option* opt = entry->value;
+                char* opt_str = option_to_str(opt);
+                printf("  %s: %s\n", entry->key, opt_str);
+                free(opt_str);
+            }
+        }
+    } else {
+        puts("  [none]");
+    }
+
+    puts("\nArguments:");
+    if (parser->positional_args->count > 0) {
+        for (int i = 0; i < parser->positional_args->count; i++) {
+            printf("  %s\n", ap_get_arg_at_index(parser, i));
+        }
+    } else {
+        puts("  [none]");
+    }
+
+    puts("\nCommand:");
+    if (ap_found_cmd(parser)) {
+        printf("  %s\n", ap_get_cmd_name(parser));
+    } else {
+        puts("  [none]");
+    }
+}
+
+
+char* ap_get_zeroth_root_arg(ArgParser* parser) {
+    return parser->root_parser->zeroth_root_arg;
+}