From 698e05081aa3dc7b2f858c9d7bb39738d07c9a67 Mon Sep 17 00:00:00 2001
From: Greg Shuflin <greg@everydayimshuflin.com>
Date: Wed, 31 Jan 2024 00:24:18 -0800
Subject: [PATCH] starting ebnf representation

---
 src/lib.rs            |  1 +
 src/representation.rs | 62 ++++++++++++++++++++++++++++++++++++++++---
 src/util.rs           | 46 ++++++++++++++++++++++++++++++++
 3 files changed, 105 insertions(+), 4 deletions(-)
 create mode 100644 src/util.rs

diff --git a/src/lib.rs b/src/lib.rs
index 7aba179..2ff5434 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@ mod parser;
 mod primitives;
 mod representation;
 mod sequence;
+mod util;
 
 #[cfg(test)]
 mod test;
diff --git a/src/representation.rs b/src/representation.rs
index 8516a0f..acd33e7 100644
--- a/src/representation.rs
+++ b/src/representation.rs
@@ -1,12 +1,66 @@
+use std::fmt;
+
+use crate::util::intersperse_option;
+
 #[derive(Debug)]
-pub struct Representation {}
+pub struct Representation {
+    production_output: EBNF,
+}
 
 impl Representation {
-    pub fn show(&self) {
-        println!("Not done");
+    pub fn show(&self) -> String {
+        self.production_output.to_string()
     }
 
     pub fn new() -> Self {
-        Self {}
+        Self {
+            production_output: EBNF::None,
+        }
+    }
+
+    pub fn with_production(production_output: EBNF) -> Self {
+        Self { production_output }
+    }
+}
+
+#[derive(Debug)]
+pub enum EBNF {
+    None,
+    CharTerminal(char),
+    Alternation(Vec<EBNF>),
+}
+
+impl fmt::Display for EBNF {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            EBNF::None => write!(f, "none"),
+            EBNF::CharTerminal(ch) => write!(f, "'{ch}'"),
+            EBNF::Alternation(items) => {
+                for item in intersperse_option(items.iter()) {
+                    match item {
+                        None => write!(f, " | ")?,
+                        Some(item) => write!(f, "{item}")?,
+                    }
+                }
+                write!(f, "")
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_ebnf_print() {
+        let example = EBNF::Alternation(vec![
+            EBNF::CharTerminal('f'),
+            EBNF::CharTerminal('a'),
+            EBNF::CharTerminal('k'),
+            EBNF::CharTerminal('e'),
+        ]);
+
+        assert_eq!(example.to_string(), "'f' | 'a' | 'k' | 'e'");
     }
 }
diff --git a/src/util.rs b/src/util.rs
new file mode 100644
index 0000000..53897e7
--- /dev/null
+++ b/src/util.rs
@@ -0,0 +1,46 @@
+use std::iter::Peekable;
+
+pub(crate) fn intersperse_option<I: Iterator>(iterator: I) -> impl Iterator<Item = Option<I::Item>>
+where
+    I::Item: Clone,
+{
+    intersperse(iterator.map(Some), None)
+}
+
+pub(crate) fn intersperse<I: Iterator>(iterator: I, separator: I::Item) -> Intersperse<I>
+where
+    I::Item: Clone,
+{
+    Intersperse {
+        inner: iterator.peekable(),
+        separator,
+        needs_sep: false,
+    }
+}
+
+pub struct Intersperse<I>
+where
+    I: Iterator,
+{
+    inner: Peekable<I>,
+    separator: I::Item,
+    needs_sep: bool,
+}
+
+impl<I> Iterator for Intersperse<I>
+where
+    I: Iterator,
+    I::Item: Clone,
+{
+    type Item = I::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.needs_sep && self.inner.peek().is_some() {
+            self.needs_sep = false;
+            Some(self.separator.clone())
+        } else {
+            self.needs_sep = true;
+            self.inner.next()
+        }
+    }
+}