1 files changed, 87 insertions, 0 deletions

diff --git a/src/lisp/expr.rs b/src/lisp/expr.rs
new file mode 100644
index 0000000..94e778f
--- /dev/null
+++ b/src/lisp/expr.rs
@@ -0,0 +1,87 @@
+use std::fmt;
+
+use crate::lisp::number::LispNumber;
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum LispExpr {
+    Number(LispNumber),
+    List(Vec<LispExpr>),
+    StringLit(String),
+    BoolLit(bool),
+    Ident(String),
+    Function(LispFunction),
+
+    // none of these depths should be zero
+    Quasiquote(Box<LispExpr>, u32),
+    Comma(Box<LispExpr>, u32),
+    CommaAt(Box<LispExpr>, u32),
+    Quote(Box<LispExpr>, u32),
+}
+
+impl LispExpr {
+    pub fn comma(self, n: u32) -> LispExpr {
+        match self {
+            LispExpr::Comma(v, i) => LispExpr::Comma(v, i.checked_add(n).expect("comma overflow")),
+            LispExpr::CommaAt(v, i) => LispExpr::CommaAt(v, i + n),
+            v => LispExpr::Comma(Box::new(v), n),
+        }
+    }
+
+    pub fn comma_at(self, n: u32) -> LispExpr {
+        match self {
+            LispExpr::CommaAt(v, i) => {
+                LispExpr::CommaAt(v, i.checked_add(n).expect("comma_at overflow"))
+            }
+            v => LispExpr::CommaAt(Box::new(v), n),
+        }
+    }
+
+    pub fn quote(self, n: u32) -> LispExpr {
+        match self {
+            LispExpr::Quote(v, i) => LispExpr::Quote(v, i.checked_add(n).expect("quote overflow")),
+            v => LispExpr::Quote(Box::new(v), n),
+        }
+    }
+
+    pub fn quasiquote(self, n: u32) -> LispExpr {
+        match self {
+            LispExpr::Quasiquote(v, i) => {
+                LispExpr::Quasiquote(v, i.checked_add(n).expect("quasiquote overflow"))
+            }
+            v => LispExpr::Quasiquote(Box::new(v), n),
+        }
+    }
+}
+
+impl fmt::Display for LispExpr {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            LispExpr::Number(n) => write!(f, "{}", n)?,
+            LispExpr::List(l) => {
+                for expr in l.iter() {
+                    write!(f, " {} ", expr)?
+                }
+            }
+            LispExpr::StringLit(s) => write!(f, "{:?}", s)?,
+            LispExpr::BoolLit(b) => {
+                if *b {
+                    write!(f, "#t")?
+                } else {
+                    write!(f, "#f")?
+                }
+            }
+            LispExpr::Ident(s) => write!(f, "{}", s)?,
+            LispExpr::Function(_) => write!(f, "<#procedure>")?,
+            LispExpr::Quasiquote(val, depth) => {
+                write!(f, "{}{}", "`".repeat(*depth as usize), val)?
+            }
+            LispExpr::Comma(val, depth) => write!(f, "{}{}", ",".repeat(*depth as usize), val)?,
+            LispExpr::CommaAt(val, depth) => write!(f, "{}@{}", ",".repeat(*depth as usize), val)?,
+            LispExpr::Quote(val, depth) => write!(f, "{}{}", "'".repeat(*depth as usize), val)?,
+        };
+        Ok(())
+    }
+}
+
+#[derive(Debug, PartialEq, Clone)]
+struct LispFunction {}