4 files changed, 154 insertions, 0 deletions
diff --git a/chewed/Cargo.toml b/chewed/Cargo.toml
new file mode 100644
index 0000000..87053bc
--- /dev/null
+++ b/chewed/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "chewed"
+version = "0.1.0"
+authors = ["Greg Brown <gmb60@cam.ac.uk>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/chewed/src/error.rs b/chewed/src/error.rs
new file mode 100644
index 0000000..cb2cc4b
--- /dev/null
+++ b/chewed/src/error.rs
@@ -0,0 +1,58 @@
+use std::{error::Error, fmt};
+
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+pub enum TakeError {
+    BadBranch(char, &'static [char]),
+    BadString(String, &'static str),
+    EndOfStream,
+}
+
+impl fmt::Display for TakeError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::BadBranch(got, expected) => {
+                write!(f, "Unexpected character {:?}.", got)?;
+
+                if expected.is_empty() {
+                    write!(f, "Expected end of input.")
+                } else if expected.len() == 1 {
+                    write!(f, "Expected character {:?}.", expected[0])
+                } else {
+                    let mut iter = expected.iter();
+                    write!(f, "Expected one of {:?}", iter.next().unwrap())?;
+
+                    for c in iter {
+                        write!(f, ", {:?}", c)?;
+                    }
+
+                    Ok(())
+                }
+            }
+            Self::BadString(got, expected) => write!(f, "Unexpected string {:?}. Expected {:?}", got, expected),
+            Self::EndOfStream => write!(f, "Unexpected end of input"),
+        }
+    }
+}
+
+impl Error for TakeError {}
+
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+pub enum ParseError {
+    TakeError(TakeError),
+    InputContinues,
+}
+
+impl fmt::Display for ParseError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::TakeError(e) => e.fmt(f),
+            Self::InputContinues => write!(f, "Expected end of input"),
+        }
+    }
+}
+
+impl From<TakeError> for ParseError {
+    fn from(e: TakeError) -> Self {
+        Self::TakeError(e)
+    }
+}
diff --git a/chewed/src/lib.rs b/chewed/src/lib.rs
new file mode 100644
index 0000000..341af9d
--- /dev/null
+++ b/chewed/src/lib.rs
@@ -0,0 +1,5 @@
+mod error;
+mod parse;
+
+pub use error::*;
+pub use parse::*;
diff --git a/chewed/src/parse.rs b/chewed/src/parse.rs
new file mode 100644
index 0000000..0687ea5
--- /dev/null
+++ b/chewed/src/parse.rs
@@ -0,0 +1,82 @@
+use super::error::{ParseError, TakeError};
+
+pub trait Parser: Iterator<Item = char> {
+    fn peek(&mut self) -> Option<char>;
+
+    fn take<P: Parse>(&mut self) -> Result<P, TakeError> {
+        P::take(self)
+    }
+
+    fn parse<P: Parse>(self) -> Result<P, ParseError>
+    where
+        Self: Sized,
+    {
+        P::parse(self)
+    }
+
+    fn take_str(&mut self, s: &'static str) -> Result<(), TakeError> {
+        let mut count = 0;
+
+        for exp in s.chars() {
+            if let Some(got) = self.peek() {
+                if got == exp {
+                    self.next();
+                    count += 1
+                } else {
+                    let mut out = String::from(&s[..count]);
+                    out.push(got);
+
+                    return Err(TakeError::BadString(out, s));
+                }
+            } else {
+                return Err(TakeError::EndOfStream);
+            }
+        }
+
+        Ok(())
+    }
+}
+
+pub trait Parse: Sized {
+    fn take<P: Parser + ?Sized>(input: &mut P) -> Result<Self, TakeError>;
+
+    fn parse<P: Parser>(mut input: P) -> Result<Self, ParseError> {
+        let res = Self::take(&mut input)?;
+
+        if input.peek().is_some() {
+            Err(ParseError::InputContinues)
+        } else {
+            Ok(res)
+        }
+    }
+}
+
+impl Parse for () {
+    fn take<P: Parser + ?Sized>(_: &mut P) -> Result<Self, TakeError> {
+        Ok(())
+    }
+}
+
+impl<A: Parse, B: Parse> Parse for (A, B) {
+    fn take<P: Parser + ?Sized>(input: &mut P) -> Result<Self, TakeError> {
+        let a = input.take()?;
+        let b = input.take()?;
+        Ok((a, b))
+    }
+
+    fn parse<P: Parser>(mut input: P) -> Result<Self, ParseError> {
+        let a = A::take(&mut input)?;
+        let b = B::parse(input)?;
+        Ok((a, b))
+    }
+}
+
+impl<T: Parse + Sized> Parse for Box<T> {
+    fn take<P: Parser + ?Sized>(input: &mut P) -> Result<Self, TakeError> {
+        Ok(Box::new(input.take()?))
+    }
+
+    fn parse<P: Parser>(input: P) -> Result<Self, ParseError> {
+        Ok(Box::new(input.parse()?))
+    }
+}