examples/sort_perf: Fix for nixos.

Make the word list specifiable with the WORDLIST environment variable,
and fall back to the hard coded /usr/share/dict/words only if that
variable is not set.  In the flake, we set the variable to a known-good
list.

Author: lorinder

examples/sort_perf.cc

@@ -164,11 +164,14 @@ static void load_dict()
 	/* Load dictionary into memory */
 	size_t dict_cap;
 	csnip_arr_Init(dict, dict_nbytes, dict_cap, 4096, _);
-	FILE* fp = fopen("/usr/share/dict/words", "r");
+	const char* wordlist = getenv("WORDLIST");
+	if (wordlist == NULL)
+		wordlist = "/usr/share/dict/words";
+	FILE* fp = fopen(wordlist, "r");
 	if (fp == 0) {
-		fprintf(stderr,
-		  "Cannot open /usr/share/dict/words\n");
-		abort();
+		fprintf(stderr, "Error:  Cannot open word list \"%s\"\n",
+			wordlist);
+		exit(1);
 	}
 	const size_t bsz = 4096;
 	size_t r = 0;

flake.nix

@@ -22,6 +22,8 @@
           ];
 
           buildInputs = with pkgs; [ ];
+
+          WORDLIST = "${pkgs.scowl}/share/dict/words.txt";
         };
       };
     });