2 files changed, 16 insertions, 1 deletions

diff --git a/src/lisp/error.rs b/src/lisp/error.rs
index f323bb8..9e9dc90 100644
--- a/src/lisp/error.rs
+++ b/src/lisp/error.rs
@@ -98,6 +98,7 @@ pub enum EvalError {
     DivByZero,
     TypeMismatch,
     NoFileName,
+    FileError(io::Error),
     AccessEmptyList,
     InvalidCoordinates((LispNumber, LispNumber)),
     AssertionError { expected: LispExpr, got: LispExpr },
@@ -126,6 +127,7 @@ impl fmt::Display for EvalError {
             Self::TypeMismatch => write!(f, "mismatched types"),
             Self::DivByZero => write!(f, "attempt to divide by zero"),
             Self::NoFileName => write!(f, "no file name specified"),
+            Self::FileError(e) => write!(f, "file error: {}", e),
             Self::AccessEmptyList => write!(f, "attempted to access empty list"),
             Self::InvalidCoordinates((x, y)) => write!(f, "invalid coordinates: {} {}", x, y),
             Self::AssertionError { expected, got } => {
diff --git a/src/lisp/prelude.rs b/src/lisp/prelude.rs
index 7cb46ff..8088510 100644
--- a/src/lisp/prelude.rs
+++ b/src/lisp/prelude.rs
@@ -14,7 +14,7 @@ use crate::{
     utils::{load_script, rect_coords},
 };
 
-use std::convert::TryInto;
+use std::{convert::TryInto, fs::File, io::BufWriter, path::Path};
 
 #[macro_export]
 macro_rules! primitive {
@@ -260,6 +260,18 @@ pub fn new_env() -> Result<Environment, LispError> {
         }
     });
 
+    primitive!(env, Arity::Exact(1), "export-png", |args, app| {
+        if let LispExpr::StringLit(s) = &args[0] {
+            let export_path = Path::new(&s);
+            let file = File::create(export_path).map_err(EvalError::FileError)?;
+            let w = BufWriter::new(file);
+            app.export().write_png(w);
+            Ok(LispExpr::Unit)
+        } else {
+            Err(EvalError::TypeMismatch.into())
+        }
+    });
+
     primitive!(env, Arity::Exact(0), "grid-enabled?", |_, app| {
         Ok(LispExpr::BoolLit(app.grid.enabled))
     });
@@ -524,5 +536,6 @@ pub fn new_env() -> Result<Environment, LispError> {
     primitive!(env, Arity::Exact(1), "id", |args, _| {
         Ok(args[0].clone())
     });
+
     Ok(env)
 }