From f98ac6b5f34983ee3afb4722c974844333049853 Mon Sep 17 00:00:00 2001
From: Colin Reeder <vpzomtrrfrt@gmail.com>
Date: Sun, 9 Sep 2018 08:15:46 -0600
Subject: [PATCH] Initial commit

---
 .gitignore   |  3 +++
 Cargo.toml   |  7 +++++
 src/lib.rs   | 11 ++++++++
 src/parse.rs | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 93 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.toml
 create mode 100644 src/lib.rs
 create mode 100644 src/parse.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6936990
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+/target
+**/*.rs.bk
+Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..752bc17
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "four"
+version = "0.1.0"
+authors = ["Colin Reeder <vpzomtrrfrt@gmail.com>"]
+
+[dependencies]
+vec1 = "1.1.0"
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..4ca7447
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,11 @@
+#[macro_use]
+extern crate vec1;
+
+pub mod parse;
+
+pub enum Expr {
+    Four,
+    Call(vec1::Vec1<Expr>)
+}
+
+pub use parse::{parse, ParseError};
diff --git a/src/parse.rs b/src/parse.rs
new file mode 100644
index 0000000..773e976
--- /dev/null
+++ b/src/parse.rs
@@ -0,0 +1,72 @@
+use std;
+
+use {Expr};
+
+pub enum ParseError {
+    TrailingCharacters,
+    UnexpectedEof,
+    EmptyBlock,
+    IOError(std::io::Error)
+}
+
+impl From<std::io::Error> for ParseError {
+    fn from(err: std::io::Error) -> ParseError {
+        ParseError::IOError(err)
+    }
+}
+
+pub fn parse(mut src: impl std::io::Read) -> Result<Expr, ParseError> {
+    let mut buf = [0];
+    let next = parse_next(&mut src, &mut buf)?;
+    let ret = src.read(&mut buf)?;
+    if ret > 0 {
+        Err(ParseError::TrailingCharacters)
+    }
+    else {
+        match next {
+            Next::EndFile => Err(ParseError::UnexpectedEof),
+            Next::EndParen => Err(ParseError::TrailingCharacters),
+            Next::Expr(expr) => Ok(expr)
+        }
+    }
+}
+
+enum Next {
+    Expr(Expr),
+    EndParen,
+    EndFile
+}
+
+fn parse_next(mut src: impl std::io::Read, buf: &mut [u8; 1]) -> Result<Next, ParseError> {
+    loop {
+        let ret = src.read(buf)?;
+        if ret < 1 {
+            return Ok(Next::EndFile);
+        }
+        if buf[0] == b'4' {
+            return Ok(Next::Expr(Expr::Four));
+        }
+        if buf[0] == b')' {
+            return Ok(Next::EndParen);
+        }
+        if buf[0] == b'(' {
+            return Ok(Next::Expr(parse_call(src, buf)?));
+        }
+    }
+}
+
+fn parse_call(mut src: impl std::io::Read, buf: &mut [u8; 1]) -> Result<Expr, ParseError> {
+    let mut args = match parse_next(&mut src, buf)? {
+        Next::EndFile => return Err(ParseError::UnexpectedEof),
+        Next::EndParen => return Err(ParseError::EmptyBlock),
+        Next::Expr(expr) => vec1![expr]
+    };
+
+    loop {
+        match parse_next(&mut src, buf)? {
+            Next::EndFile => return Err(ParseError::UnexpectedEof),
+            Next::EndParen => return Ok(Expr::Call(args)),
+            Next::Expr(expr) => args.push(expr)
+        }
+    }
+}