Add a bunch of character stuff to the lexer module

src/lexer.rs

@@ -0,0 +1,56 @@
+//! # Lexer
+
+mod characters {
+    use std::collections::HashSet;
+    use std::iter::FromIterator;
+    
+    pub type CharSet = HashSet<char>;
+
+    pub fn ascii_letters() -> CharSet {
+        let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".chars();
+        return CharSet::from_iter(letters);
+    }
+
+    pub fn ascii_digits() -> CharSet {
+        let digits = "1234567890".chars();
+        return CharSet::from_iter(digits);
+    }
+
+    pub fn identifier_initials() -> CharSet {
+        let letters = ascii_letters();
+        let extras = CharSet::from_iter("!$%&*/:<=>?~_^".chars());
+        let mut initials = CharSet::new();
+        initials.extend(letters.iter());
+        initials.extend(extras.iter());
+        return initials;
+    }
+
+    pub fn identifier_subsequents() -> CharSet {
+        let initials = identifier_initials();
+        let digits = ascii_digits();
+        let extras = CharSet::from_iter(".+-".chars());
+        let mut subsequents = CharSet::new();
+        subsequents.extend(initials.iter());
+        subsequents.extend(digits.iter());
+        subsequents.extend(extras.iter());
+        return subsequents;
+    }
+}
+
+enum Kind {
+    LeftParen,
+    RightParen,
+    Identifier,
+}
+
+struct Token {
+    kind: Kind,
+    value: String,
+}
+
+pub fn hello(person: &str) {
+    println!("Hello, {}!", person);
+    for (idx, c) in person.char_indices() {
+        println!("  {}, {} -> {}", c, idx, characters::ascii_letters().contains(&c));
+    }
+}

src/main.rs

@@ -1,3 +1,8 @@
+mod lexer;
+
 fn main() {
-    println!("Hello, world!");
+    lexer::hello("Eryn");
+    lexer::hello("Emily");
+    let s = "Jonas".to_string();
+    lexer::hello(&s);
 }