update

src/lexer/mod.rs

@@ -0,0 +1,23 @@
+struct Lexer {
+    input: String,
+    position: Option<i32>,
+    read_pos: Option<i32>,
+    ch: Option<i8>,
+}
+
+fn new(input_str: String) -> Lexer {
+    let l: Lexer = Lexer {
+        input: input_str,
+        position: None,
+        read_pos: None,
+        ch: None,
+    };
+    l
+}
+
+fn read_char(l: Lexer) {
+    let read_pos = usize::try_from(l.read_pos.unwrap());
+    if read_pos >= l.input.len() {
+        l.ch = 0;
+    }
+}