Add expression parsing

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/syn/ast.rs

@@ -1,11 +1,29 @@
 use crate::syn::{op::*, span::*};
+use derivative::Derivative;
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Stmt {
+    Assign(Expr, Expr),
+    Expr(Expr),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Expr {
     Base(BaseExpr),
     Bin(Box<BinExpr>),
     Un(Box<UnExpr>),
 }
 
+impl Spanned for Expr {
+    fn span(&self) -> Span {
+        match self {
+            Expr::Base(b) => b.span(),
+            Expr::Bin(b) => b.span(),
+            Expr::Un(u) => u.span(),
+        }
+    }
+}
+
 impl From<UnExpr> for Expr {
     fn from(un: UnExpr) -> Self {
         Expr::Un(Box::new(un))
@@ -24,18 +42,38 @@ impl From<BaseExpr> for Expr {
     }
 }
 
+#[derive(Derivative, Clone, PartialEq, Eq)]
+#[derivative(Debug)]
 pub struct BinExpr {
     pub lhs: Expr,
     pub op: BinOp,
     pub rhs: Expr,
-}
-
-pub struct UnExpr {
-    pub op: UnOp,
-    pub expr: Expr,
+    #[derivative(Debug = "ignore")]
     pub span: Span,
 }
 
+impl Spanned for BinExpr {
+    fn span(&self) -> Span {
+        self.span
+    }
+}
+
+#[derive(Derivative, Clone, PartialEq, Eq)]
+#[derivative(Debug)]
+pub struct UnExpr {
+    pub op: UnOp,
+    pub expr: Expr,
+    #[derivative(Debug = "ignore")]
+    pub span: Span,
+}
+
+impl Spanned for UnExpr {
+    fn span(&self) -> Span {
+        self.span
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum BaseExprKind {
     Ident,
     Num,
@@ -46,7 +84,16 @@ pub enum BaseExprKind {
     Tuple(Vec<Expr>),
 }
 
+#[derive(Derivative, Clone, PartialEq, Eq)]
+#[derivative(Debug)]
 pub struct BaseExpr {
     pub kind: BaseExprKind,
+    #[derivative(Debug = "ignore")]
     pub span: Span,
 }
+
+impl Spanned for BaseExpr {
+    fn span(&self) -> Span {
+        self.span
+    }
+}