From 4debd88807c538aa430ce69b83fdb291f687b1b1 Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rosehogenson@posteo.net>
Date: Mon, 27 May 2024 16:04:31 -0700
Subject: Rewrite in Rust.

---
 src/lexer.rs | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 src/lexer.rs

(limited to 'src/lexer.rs')

diff --git a/src/lexer.rs b/src/lexer.rs
new file mode 100644
index 0000000..49d2d04
--- /dev/null
+++ b/src/lexer.rs
@@ -0,0 +1,74 @@
+pub struct Lexer<'a> {
+    pub buf: &'a str,
+}
+
+impl<'a> Lexer<'a> {
+    fn skip_whitespace(&mut self) {
+        while let Some(b' ') = self.buf.as_bytes().first() {
+            self.buf = &self.buf[1..]
+        }
+    }
+
+    fn parse_num(&mut self) -> Option<&'a str> {
+        let mut i = 0;
+        while matches!(self.buf.as_bytes().get(i), Some(&b) if b.is_ascii_digit()) {
+            i += 1;
+        }
+        if let Some(b'.') = self.buf.as_bytes().get(i) {
+            i += 1;
+        }
+        while matches!(self.buf.as_bytes().get(i), Some(&b) if b.is_ascii_digit()) {
+            i += 1;
+        }
+        let (Some(b'e') | Some(b'E')) = self.buf.as_bytes().get(i) else {
+            let t = &self.buf[..i];
+            self.buf = &self.buf[i..];
+            return Some(t);
+        };
+        i += 1;
+        if let Some(b'-') = self.buf.as_bytes().get(i) {
+            i += 1;
+        }
+        while matches!(self.buf.as_bytes().get(i), Some(&b) if b.is_ascii_digit()) {
+            i += 1;
+        }
+        let t = &self.buf[..i];
+        self.buf = &self.buf[i..];
+        Some(t)
+    }
+}
+
+impl<'a> Iterator for Lexer<'a> {
+    type Item = &'a str;
+
+    fn next(&mut self) -> Option<&'a str> {
+        self.skip_whitespace();
+        let &first_byte = self.buf.as_bytes().first()?;
+        if first_byte.is_ascii_digit() || first_byte == b'.' {
+            return self.parse_num();
+        }
+        match first_byte {
+            b'/' => {
+                if let Some(b'/') = self.buf.as_bytes().get(1) {
+                    self.buf = &self.buf[2..];
+                    return Some("//");
+                }
+                self.buf = &self.buf[1..];
+                return Some("/");
+            }
+            b'+' | b'-' | b'*' | b'^' | b'(' | b')' => {
+                let t = &self.buf[..1];
+                self.buf = &self.buf[1..];
+                return Some(t);
+            }
+            _ => (),
+        }
+        let mut i = 0;
+        while let Some(b'a'..=b'z' | b'A'..=b'Z' | b'0'..=b'9') = self.buf.as_bytes().get(i) {
+            i += 1;
+        }
+        let t = &self.buf[..i];
+        self.buf = &self.buf[i..];
+        Some(t)
+    }
+}
-- 
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