From b03cccb8dd9c72d14998f8c3cd49f43131a6ef88 Mon Sep 17 00:00:00 2001
From: Chris Mounce <christophermounce@gmail.com>
Date: Wed, 30 Apr 2025 00:12:04 -0700
Subject: [PATCH] Partial work toward a PEG parser library

---
 src/labels/labels.rs  | 14 +++++++
 src/labels/mod.rs     |  1 +
 src/main.rs           |  1 +
 src/preprocess/mod.rs |  1 +
 src/preprocess/peg.rs | 93 +++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 110 insertions(+)
 create mode 100644 src/labels/labels.rs
 create mode 100644 src/labels/mod.rs
 create mode 100644 src/preprocess/peg.rs

diff --git a/src/labels/labels.rs b/src/labels/labels.rs
new file mode 100644
index 0000000..4bc8c1d
--- /dev/null
+++ b/src/labels/labels.rs
@@ -0,0 +1,14 @@
+use super::super::preprocess::peg::Parser;
+use anyhow::Result;
+
+fn parse_program(p: &mut Parser) -> Result<()> {
+    p.star(|p| parse_line(p))?;
+    p.eof()?;
+    Ok(())
+}
+
+fn parse_line(p: &mut Parser) -> Result<()> {
+    p.star(|p| p.char(|c| c != '\n'))?;
+    p.literal("\n")?;
+    Ok(())
+}
diff --git a/src/labels/mod.rs b/src/labels/mod.rs
new file mode 100644
index 0000000..988d57b
--- /dev/null
+++ b/src/labels/mod.rs
@@ -0,0 +1 @@
+pub mod labels;
diff --git a/src/main.rs b/src/main.rs
index b998f14..1df52a0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,5 @@
 mod encoding;
+mod labels;
 mod preprocess;
 mod world;
 
diff --git a/src/preprocess/mod.rs b/src/preprocess/mod.rs
index d45ed7b..78eb8f4 100644
--- a/src/preprocess/mod.rs
+++ b/src/preprocess/mod.rs
@@ -1,3 +1,4 @@
 pub mod eval;
 pub mod parse;
+pub mod peg;
 pub mod scan;
diff --git a/src/preprocess/peg.rs b/src/preprocess/peg.rs
new file mode 100644
index 0000000..bb77ade
--- /dev/null
+++ b/src/preprocess/peg.rs
@@ -0,0 +1,93 @@
+use anyhow::{Result, anyhow, bail};
+
+// TODO: Add offsets
+pub enum Tag {
+    Open(&'static str),
+    Close,
+}
+pub struct Parser {
+    input: String,
+    offset: usize,
+    output: Vec<Tag>,
+}
+
+#[derive(Clone, Copy)]
+pub struct Savepoint {
+    offset: usize,
+    num_tags: usize,
+}
+
+impl Parser {
+    pub fn new(input: &str) -> Self {
+        Self {
+            input: input.into(),
+            offset: 0,
+            output: Vec::new(),
+        }
+    }
+
+    pub fn save(&self) -> Savepoint {
+        Savepoint {
+            offset: self.offset,
+            num_tags: self.output.len(),
+        }
+    }
+
+    pub fn restore(&mut self, sp: Savepoint) {
+        self.offset = sp.offset;
+        self.output.truncate(sp.num_tags);
+    }
+
+    pub fn eof(&mut self) -> Result<()> {
+        if self.input.len() == self.offset {
+            Ok(())
+        } else {
+            bail!("No match")
+        }
+    }
+
+    pub fn literal(&mut self, str: &str) -> Result<()> {
+        if self.input[self.offset..].starts_with(str) {
+            self.offset += str.len();
+            Ok(())
+        } else {
+            bail!("No match")
+        }
+    }
+
+    pub fn char<F>(&mut self, f: F) -> Result<()>
+    where
+        F: Fn(char) -> bool,
+    {
+        if let Some(c) = self.input[self.offset..].chars().next() {
+            if f(c) {
+                self.offset += c.len_utf8();
+                return Ok(());
+            }
+        }
+        bail!("No match")
+    }
+
+    pub fn star<F>(&mut self, mut f: F) -> Result<()>
+    where
+        F: FnMut(&mut Self) -> Result<()>,
+    {
+        let mut sp = self.save();
+        while let Ok(_) = f(self) {
+            sp = self.save();
+        }
+        self.restore(sp);
+        Ok(())
+    }
+}
+
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_hello() {
+        let mut p = Parser::new("foo");
+        p.literal("f").unwrap();
+        p.star(|p| p.literal("o")).unwrap();
+    }
+}