cc -o mtl-arc -std=c11 mtl-arc.c
  mtl-arc.c: In function ‘new_sym’:
  mtl-arc.c:46:2: warning: implicit declaration of function ‘strdup’ [-Wimplicit-function-declaration]
    symname(result) = strdup(sym);
    ^
  mtl-arc.c:46:18: warning: assignment makes pointer from integer without a cast [enabled by default]
    symname(result) = strdup(sym);
                    ^
  mtl-arc.c: In function ‘new_string’:
  mtl-arc.c:59:20: warning: assignment makes pointer from integer without a cast [enabled by default]
    stringval(result) = strdup(string);
                      ^
  mtl-arc.c: In function ‘new_builtin’:
  mtl-arc.c:118:15: warning: assignment makes pointer from integer without a cast [enabled by default]
    help(result) = strdup(doc);
                 ^
  mtl-arc.c: In function ‘char_to_token’:
  mtl-arc.c:170:2: warning: return makes pointer from integer without a cast [enabled by default]
    return strdup(cbuf);
    ^
  mtl-arc.c: In function ‘split_string’:
  mtl-arc.c:194:20: warning: assignment makes pointer from integer without a cast [enabled by default]
      *(result + i++) = strdup(token);
                      ^
  mtl-arc.c: In function ‘buf_to_string’:
  mtl-arc.c:212:2: warning: return makes pointer from integer without a cast [enabled by default]
    return strdup(buf);
    ^
  mtl-arc.c: In function ‘read_expr’:
  mtl-arc.c:327:4: warning: passing argument 1 of ‘split_string’ makes pointer from integer without a cast [enabled by default]
      char **nums = split_string(strdup(token), '/');
      ^
  mtl-arc.c:181:8: note: expected ‘char *’ but argument is of type ‘int’
   char **split_string(char *a_str, const char a_delim) {
          ^
  /tmp/ccMru0iN.o: In function `builtin_cos':
  mtl-arc.c:(.text+0x3b0e): undefined reference to `sin'
  /tmp/ccMru0iN.o: In function `builtin_expt':
  mtl-arc.c:(.text+0x3bd2): undefined reference to `pow'
  /tmp/ccMru0iN.o: In function `builtin_log':
  mtl-arc.c:(.text+0x3c53): undefined reference to `log'
  /tmp/ccMru0iN.o: In function `builtin_rand':
  mtl-arc.c:(.text+0x3db2): undefined reference to `floor'
  /tmp/ccMru0iN.o: In function `builtin_sin':
  mtl-arc.c:(.text+0x3e46): undefined reference to `sin'
  /tmp/ccMru0iN.o: In function `builtin_sqrt':
  mtl-arc.c:(.text+0x3ec7): undefined reference to `sqrt'
  /tmp/ccMru0iN.o: In function `builtin_tan':
  mtl-arc.c:(.text+0x3f48): undefined reference to `tan'
  /tmp/ccMru0iN.o: In function `builtin_trunc':
  mtl-arc.c:(.text+0x3fc9): undefined reference to `trunc'
  collect2: error: ld returned 1 exit status
  make: *** [all] Error 1