c_cpp 可评估语言的第一个原型

Posted 2021-05-14

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

// Prototype for evaluatable expression
// ....... structure .........
// <val> <op> <args> ... <op>
// Or, other form is
// <val> <op> <args>  <term> ... <new exp>

#define TYPE_STOP  0
#define TYPE_SET   1
#define TYPE_INT   2
#define TYPE_PLUS  3
#define TYPE_SUB   4
#define TYPE_PRINT 5

#define TYPE_INT_SIZE (sizeof(int) + 1)

typedef unsigned char eval_t;


void eval_exp(eval_t* exp)
{
   eval_t* current = NULL;
   eval_t op = 0;
   goto STATE_BASE;
STATE_BASE:
   switch(*exp)
   {
      case TYPE_INT:
           current = exp;
           exp += TYPE_INT_SIZE;
           goto STATE_INT_CUR;
      case TYPE_STOP:
           return;
      default:
           goto STATE_UNKNOWN_BYTE;
   }
STATE_INT_CUR:
   switch(*exp)
   {
      case TYPE_INT:
           eval_exp(exp);
           goto STATE_BASE;
      case TYPE_PLUS:
           exp++;
           goto STATE_PLUS_INT_OP;
      case TYPE_SUB:
           exp++;
           goto STATE_SUB_INT_OP;
      case TYPE_STOP:
           exp++;
           // This type eval has finished 
           goto STATE_BASE;   
      default:
           fprintf(stderr, "Op Error: Unsupported op %u for type <int>\n", *exp);
           exit(1);
   }
STATE_PLUS_INT_OP:
   switch(*exp)
   {
      case TYPE_INT:
           exp++;
           *(int*)(current + 1) += *(int*)(exp);
           exp += sizeof(int);
           goto STATE_INT_CUR;
      case TYPE_PLUS:
           goto STATE_DUP_OP;
      case TYPE_SUB:
           goto STATE_BAD_OP_PLUS;
      case TYPE_STOP:
          goto STATE_INT_CUR;
   }
STATE_UNKNOWN_BYTE:
   fprintf(stderr, "Unknown byte: %u found in expression, exiting...\n", *exp);
   exit(1);
STATE_DUP_OP:
   fprintf(stderr, "Found duplicate of op %u, exiting...\n", *exp);
   exit(1);
STATE_BAD_OP_PLUS:
   fprintf(stderr, "Found illegal op %u, for <plus> op, exiting...\n", *exp);
   exit(1);
}


int main(void) {
    printf("Hello World\n");
    return 0;
}