From eb280a903f8f20d0b0c0ef5acae955a20929d100 Mon Sep 17 00:00:00 2001
From: Greg Brown <gmb60@cam.ac.uk>
Date: Wed, 6 Jan 2021 16:36:46 +0000
Subject: Create Chewed, the consumer crate.

---
 chewed/src/parse.rs | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)
 create mode 100644 chewed/src/parse.rs

(limited to 'chewed/src/parse.rs')

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()?))
+    }
+}
-- 
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