参考

{% collapse title=”evaluation.c” %}

  1. #include "mpc.h"
  3. #ifdef _WIN32
  5. static char buffer[2048];
  7. char* readline(char* prompt) {
  8.   fputs(prompt, stdout);
  9.   fgets(buffer, 2048, stdin);
  10.   char* cpy = malloc(strlen(buffer)+1);
  11.   strcpy(cpy, buffer);
  12.   cpy[strlen(cpy)-1] = '\0';
  13.   return cpy;
  14. }
  16. void add_history(char* unused) {}
  18. #else
  19. #include <editline/readline.h>
  20. #include <editline/history.h>
  21. #endif
  23. /* Use operator string to see which operation to perform */
  24. long eval_op(long x, char* op, long y) {
  25.   if (strcmp(op, "+") == 0) { return x + y; }
  26.   if (strcmp(op, "-") == 0) { return x - y; }
  27.   if (strcmp(op, "*") == 0) { return x * y; }
  28.   if (strcmp(op, "/") == 0) { return x / y; }
  29.   return 0;
  30. }
  32. long eval(mpc_ast_t* t) {
  34.   /* If tagged as number return it directly. */ 
  35.   if (strstr(t->tag, "number")) {
  36.     return atoi(t->contents);
  37.   }
  39.   /* The operator is always second child. */
  40.   char* op = t->children[1]->contents;
  42.   /* We store the third child in `x` */
  43.   long x = eval(t->children[2]);
  45.   /* Iterate the remaining children and combining. */
  46.   int i = 3;
  47.   while (strstr(t->children[i]->tag, "expr")) {
  48.     x = eval_op(x, op, eval(t->children[i]));
  49.     i++;
  50.   }
  52.   return x;  
  53. }
  55. int main(int argc, char** argv) {
  57.   mpc_parser_t* Number = mpc_new("number");
  58.   mpc_parser_t* Operator = mpc_new("operator");
  59.   mpc_parser_t* Expr = mpc_new("expr");
  60.   mpc_parser_t* Lispy = mpc_new("lispy");
  62.   mpca_lang(MPCA_LANG_DEFAULT,
  63.     "                                                     \
  64.       number   : /-?[0-9]+/ ;                             \
  65.       operator : '+' | '-' | '*' | '/' ;                  \
  66.       expr     : <number> | '(' <operator> <expr>+ ')' ;  \
  67.       lispy    : /^/ <operator> <expr>+ /$/ ;             \
  68.     ",
  69.     Number, Operator, Expr, Lispy);
  71.   puts("Lispy Version 0.0.0.0.3");
  72.   puts("Press Ctrl+c to Exit\n");
  74.   while (1) {
  76.     char* input = readline("lispy> ");
  77.     add_history(input);
  79.     mpc_result_t r;
  80.     if (mpc_parse("<stdin>", input, Lispy, &r)) {
  82.       long result = eval(r.output);
  83.       printf("%li\n", result);
  84.       mpc_ast_delete(r.output);
  86.     } else {    
  87.       mpc_err_print(r.error);
  88.       mpc_err_delete(r.error);
  89.     }
  91.     free(input);
  93.   }
  95.   mpc_cleanup(4, Number, Operator, Expr, Lispy);
  97.   return 0;
  98. }

{% endcollapse %}