test3.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

typedef enum { BOOLEAN, CHARACTER, STRING, NUMBER, SYMBOL } object_type;

typedef union {
  struct { char value; } boolean;
  struct { char value; } character;
  struct { char *value; } string;
  struct { long value; } number;
  struct { char *value; } symbol;
} object_data;

typedef struct {
  object_type type;
  object_data data;
} object;

#define IS_BOOLEAN(object) ((object)->type == BOOLEAN)
#define IS_CHARACTER(object) ((object)->type == CHARACTER)
#define IS_STRING(object) ((object)->type == STRING)
#define IS_NUMBER(object) ((object)->type == NUMBER)
#define IS_SYMBOL(object) ((object)->type == SYMBOL)

#define BOOLEAN_VALUE(object) ((object)->data.boolean.value)
#define CHARACTER_VALUE(object) ((object)->data.character.value)
#define STRING_VALUE(object) ((object)->data.string.value)
#define NUMBER_VALUE(object) ((object)->data.number.value)
#define SYMBOL_VALUE(object) ((object)->data.symbol.value)

object *true;
object *false;

#define IS_TRUE(object) ((object) == true)
#define IS_FALSE(object) (!IS_TRUE(object))

#define MALLOC_CHECK(ptr) ({ if ((ptr) == NULL) { fprintf(stderr, "[%s] malloc failed\n", __func__); exit(EXIT_FAILURE); } })

object *allocate_object() {
  object *ptr = malloc(sizeof(object));

  MALLOC_CHECK(ptr);

  return ptr;
}

object *make_boolean(int value) {
  object *ptr = allocate_object();

  ptr->type = BOOLEAN;
  BOOLEAN_VALUE(ptr) = value;

  return ptr;
}

object *make_character(char value) {
  object *ptr = allocate_object();

  ptr->type = CHARACTER;
  CHARACTER_VALUE(ptr) = value;

  return ptr;
}

object *make_string(const char *value) {
  object *ptr = allocate_object();

  ptr->type = STRING;
  STRING_VALUE(ptr) = malloc(strlen(value) + 1);
  MALLOC_CHECK(STRING_VALUE(ptr));
  strcpy(STRING_VALUE(ptr), value);

  return ptr;
}

object *make_number(long value) {
  object *ptr = allocate_object();

  ptr->type = NUMBER;
  NUMBER_VALUE(ptr) = value;

  return ptr;
}

void print_object(const object *obj) {
  switch (obj->type) {
  case BOOLEAN:
	printf("#%c", IS_TRUE(obj) ? 't' : 'f');
	break;
  case CHARACTER: {
	char c = CHARACTER_VALUE(obj);

	printf("#\\");
	switch (c) {
	case '\n':
	  printf("newline");
	  break;
	case ' ':
	  printf("space");
	  break;
	default:
	  putchar(c);
	}
	break;
  }
  case STRING: {
	char *string = STRING_VALUE(obj);

	putchar('"');
	while ((*string) != '\0') {
	  switch (*string) {
	  case '\n':
		printf("\\n");
		break;
	  case '\\':
		printf("\\\\");
		break;
	  case '"':
		printf("\\\"");
		break;
	  default:
		putchar(*string);
	  }
	  string++;
	}
	putchar('"');
	break;
  }
  case NUMBER:
	printf("%d", NUMBER_VALUE(obj));
	break;
  case SYMBOL:
	printf("%s", SYMBOL_VALUE(obj));
	break;
  default:
	fprintf(stderr, "unknown type\n");
	exit(EXIT_FAILURE);
  }
}

object *read_object(FILE *input) {
  int c;

  c = getc(input);

  if (c == '#') {
	c = getc(input);

	switch (c) {
	case 't':
	  return true;
	case 'f':
	  return false;
	}
  }

  return false;
}

object *evaluate_object(object *obj) {
  return obj;
}

void repl(FILE *input) {
  do {
	printf("evaluate> ");
	print_object(evaluate_object(read_object(input)));
	printf("\n");
  } while (1);
}

int main(int argc, char *argv[]) {
  true = make_boolean(1);
  false = make_boolean(0);

  /* print_object(true); */
  /* print_object(false); */
  /* print_object(make_character('a')); */
  /* print_object(make_string("string")); */
  /* print_object(make_number(1)); */
  repl(stdin);

  return EXIT_SUCCESS;
}