From 0141e8e8c7f3e295d57990fdce6019e2d777aed0 Mon Sep 17 00:00:00 2001
From: Greg Brown <gmb60@cam.ac.uk>
Date: Wed, 18 Nov 2020 13:31:27 +0000
Subject: Convert concrete to abstract syntax tree

---
 src/ast/convert.rs | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 src/ast/convert.rs

(limited to 'src/ast/convert.rs')

diff --git a/src/ast/convert.rs b/src/ast/convert.rs
new file mode 100644
index 0000000..c27c75f
--- /dev/null
+++ b/src/ast/convert.rs
@@ -0,0 +1,76 @@
+use super::Term;
+
+#[derive(Clone, Debug, Default)]
+pub struct Context {
+    vars: Vec<String>,
+}
+
+impl Context {
+    /// # Examples
+    /// ```
+    /// use chomp::ast::convert::Context;
+    ///
+    /// let context = Context::new();
+    /// assert_eq!(context.get("x"), None);
+    /// assert_eq!(context.get("y"), None);
+    /// assert_eq!(context.get("z"), None);
+    /// ```
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// # Examples
+    /// ```
+    /// use chomp::ast::convert::Context;
+    ///
+    /// let context = Context::new();
+    /// assert_eq!(context.get("x"), None);
+    ///
+    /// context.push("x".to_owned(), |c| {
+    ///     assert_eq!(c.get("x"), Some(0));
+    ///
+    ///     c.push("y".to_owned(), |c| {
+    ///         assert_eq!(c.get("x"), Some(1));
+    ///     })
+    /// });
+    ///
+    /// assert_eq!(context.get("x"), None);
+    /// ```
+    pub fn get<T: ?Sized + PartialEq<str>>(&self, name: &T) -> Option<usize> {
+        let mut iter = self.vars.iter();
+        let mut pos = 0;
+
+        while let Some(var) = iter.next_back() {
+            if T::eq(&name, &var) {
+                return Some(pos);
+            } else {
+                pos += 1;
+            }
+        }
+
+        None
+    }
+
+    /// # Examples
+    /// ```
+    /// use chomp::ast::convert::Context;
+    ///
+    /// let context = Context::new();
+    /// assert_eq!(context.get("x"), None);
+    ///
+    /// context.push("x".to_owned(), |c| {
+    ///     assert_eq!(c.get("x"), Some(0));
+    /// });
+    ///
+    /// assert_eq!(context.get("x"), None);
+    /// ```
+    pub fn push<F: FnOnce(&Self) -> T, T>(&self, var: String, f: F) -> T {
+        let mut context = self.clone();
+        context.vars.push(var);
+        f(&context)
+    }
+}
+
+pub trait Convert {
+    fn convert(self, context: &Context) -> Term;
+}
-- 
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