1 files changed, 117 insertions, 0 deletions

diff --git a/src/lisp/env.rs b/src/lisp/env.rs
new file mode 100644
index 0000000..ad7cc2b
--- /dev/null
+++ b/src/lisp/env.rs
@@ -0,0 +1,117 @@
+use crate::{
+    app::AppState,
+    lisp::{error::LispError, expr::LispExpr, number::LispNumber, Environment},
+};
+
+pub fn is_bound<S: AsRef<str>>(env: &mut Environment, name: S) -> bool {
+    env.get(name.as_ref()).is_some()
+}
+
+pub fn new_binding<S: AsRef<str>>(env: &mut Environment, name: S, value: LispExpr) {
+    let _ = env.insert(name.as_ref().into(), value);
+}
+
+pub fn with_prelude() -> Environment {
+    let mut env = Environment::new();
+    new_binding(
+        &mut env,
+        "+",
+        LispExpr::PrimitiveFunc(|args, _| {
+            if args.iter().any(|arg| !matches!(arg, LispExpr::Number(_))) {
+                Err(LispError::EvalError)
+            } else {
+                let result = args
+                    .iter()
+                    .map(|n| unwrap_number(n))
+                    .fold(LispNumber::Integer(0), |acc, x| acc + *x);
+                Ok(LispExpr::Number(result))
+            }
+        }),
+    );
+    env
+}
+
+pub fn eval(expr: &LispExpr, app: &mut AppState) -> Result<LispExpr, LispError> {
+    let env = &mut app.lisp_env;
+    match expr {
+        LispExpr::Unit => Ok(expr.clone()),
+        LispExpr::StringLit(_) => Ok(expr.clone()),
+        LispExpr::Number(_) => Ok(expr.clone()),
+        LispExpr::BoolLit(_) => Ok(expr.clone()),
+        LispExpr::Ident(ref id) => env
+            .get(id)
+            .ok_or_else(|| LispError::EvalError)
+            .map(Clone::clone),
+        LispExpr::List(li) => {
+            let head = &li[0];
+            match head {
+                LispExpr::Ident(func) => {
+                    let func_expr = env
+                        .get(func)
+                        .map(Clone::clone)
+                        .ok_or_else(|| LispError::EvalError)?;
+                    match func_expr {
+                        LispExpr::PrimitiveFunc(f) => {
+                            let mut args = Vec::new();
+                            for item in li[1..].iter() {
+                                args.push(eval(item, app)?);
+                            }
+                            (f)(&args, None)
+                        }
+                        _ => Err(LispError::EvalError),
+                    }
+                }
+                LispExpr::List(_) => {
+                    // TODO
+                    todo!();
+                }
+                _ => Err(LispError::EvalError),
+            }
+        }
+        _ => Err(LispError::ParseError),
+    }
+}
+
+pub fn unwrap_number(n: &LispExpr) -> &LispNumber {
+    match n {
+        LispExpr::Number(i) => i,
+        _ => panic!("unwrap_number expected number"),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn eval_primitive_call() {
+        let mut env = Environment::new();
+        new_binding(&mut env, "age", LispExpr::Number(LispNumber::Float(1.4)));
+        new_binding(
+            &mut env,
+            "+",
+            LispExpr::PrimitiveFunc(|args, _| {
+                if args.iter().any(|arg| !matches!(arg, LispExpr::Number(_))) {
+                    Err(LispError::EvalError)
+                } else {
+                    let result = args
+                        .iter()
+                        .map(|n| unwrap_number(n))
+                        .fold(LispNumber::Integer(0), |acc, x| acc + *x);
+                    Ok(LispExpr::Number(result))
+                }
+            }),
+        );
+        let mut numbers = (1..=3)
+            .map(LispNumber::Integer)
+            .map(LispExpr::Number)
+            .collect::<Vec<_>>();
+        let mut expr = Vec::new();
+        expr.push(LispExpr::Ident("+".into()));
+        expr.append(&mut numbers);
+        // assert!(matches!(
+        //     eval(&LispExpr::List(expr), ).unwrap(),
+        //     LispExpr::Number(LispNumber::Integer(6))
+        // ));
+    }
+}