repl: fgets-based readline alternative

repl.c

@@ -1,8 +1,36 @@
 #include "tinyexpr.h"
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
+
+#ifndef NO_READLINE
 #include <readline/readline.h>
 #include <readline/history.h>
+#else
+static char *readline(const char *prompt) {
+    fprintf(stderr, "%s", prompt);
+    char buf[1024];
+    char *line = fgets(buf, sizeof(buf), stdin);
+    if (line == NULL && feof(stdin)) {
+        return NULL;
+    } else if (line == NULL) {
+        perror("fgets");
+        return NULL;
+    }
+
+    size_t len = strlen(line);
+    if (line[len - 1] == '\n') {
+        line[len - 1] = '\0';
+        len -= 1;
+    }
+
+    line = malloc(len + 1);
+    strcpy(line, buf);
+    return line;
+}
+
+static void add_history(const char *line) {}
+#endif
 
 static int eval(const char *str) {
     int err = 0;