1 files changed, 55 insertions, 0 deletions
diff --git a/src/ast.rs b/src/ast.rs
new file mode 100644
index 0000000..9202968
--- /dev/null
+++ b/src/ast.rs
@@ -0,0 +1,55 @@
+// Bidirectional type checking, simple types for effects (or perhaps subtyping?) and typeclasses
+
+use core::fmt;
+use std::collections::HashMap;
+
+pub type Identifier = String;
+pub type Context = HashMap<Identifier, Term>;
+
+// note: when comes the time, we'll put effects in here (i think)
+#[derive(Clone, PartialEq, Eq)]
+pub enum Expression {
+    Annotation{expr: Box<Expression>, kind: Type},
+    Constant{term: Term},
+    Variable{id: Identifier},
+    Abstraction{param: Identifier, func: Box<Expression>},
+    Application{func: Box<Expression>, arg: Box<Expression>},
+    Conditional{if_cond: Box<Expression>, if_then: Box<Expression>, if_else: Box<Expression>}
+}
+
+// _every_ type in our language is represented as this and interpreted as a type.
+// how to store more data than fits... hmm
+pub type Value = i8;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum Type {
+    Empty,
+    Unit,
+    Bool,
+    Natural,
+    // Float,
+    // String,
+    // Enum(Vec<Type>),
+    // Record(Vec<Type>),
+    // Function{from: Box<Type>, to: Box<Type>},
+}
+
+// this means that functions cannot have types? unless we put them as empty values ig
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub struct Term {
+    pub val: Value,
+    pub kind: Type, // currently useless / redundant: will be useful for casting
+}
+
+impl fmt::Debug for Expression {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Expression::Annotation { expr, kind } => write!(f, "{:?}:{:?}", expr, kind),
+            Expression::Constant { term } => write!(f, "{}", term.val),
+            Expression::Variable { id } => write!(f, "{}", id),
+            Expression::Abstraction { param, func } => write!(f, "(λ{}.{:?})", param, func),
+            Expression::Application { func, arg } => write!(f, "{:?} {:?}", func, arg),
+            Expression::Conditional { if_cond, if_then, if_else } => write!(f, "if {:?} then {:?} else {:?}", if_cond, if_then, if_else),
+        }
+    }
+}