Convert concrete to abstract syntax tree

2 files changed, 91 insertions, 0 deletions

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;
+}
diff --git a/src/ast/mod.rs b/src/ast/mod.rs
new file mode 100644
index 0000000..1fa7d23
--- /dev/null
+++ b/src/ast/mod.rs
@@ -0,0 +1,15 @@
+pub mod convert;
+
+type Ident = String;
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum Term {
+    Epsilon,
+    Bottom,
+    Literal(String),
+    Cat(Box<Term>, Box<Term>),
+    Alt(Box<Term>, Box<Term>),
+    Fix(Box<Term>), // Uses de Bruijn indices
+    Variable(usize),
+    Call(Ident, Vec<Term>),
+}