diff --git a/src/builtins/mod.rs b/src/builtins/mod.rs
index 12052e976..81bf00d15 100644
--- a/src/builtins/mod.rs
+++ b/src/builtins/mod.rs
@@ -8,7 +8,7 @@ use hvmc::{ast, host::Host, stdlib::LogDef};
 use crate::{
   readback_hvmc,
   term::{
-    builtins::{SCONS, SNIL},
+    builtins::{RESULT_ERR, RESULT_OK, SCONS, SNIL},
     term_to_net::Labels,
     AdtEncoding, Book, Term,
   },
@@ -27,7 +27,8 @@ pub mod util;
 pub const CORE_BUILTINS: [&str; 7] =
   ["HVM.log", "HVM.black_box", "HVM.print", "HVM.query", "HVM.store", "HVM.load", "HVM.exit"];
 /// List of definition names used by the core builtins
-pub const CORE_BUILTINS_USES: [&[&str]; 7] = [&[], &[], &[], &[SCONS, SNIL], &[], &[], &[]];
+pub const CORE_BUILTINS_USES: [&[&str]; 7] =
+  [&[], &[], &[], &[SCONS, SNIL], &[RESULT_OK, RESULT_ERR], &[RESULT_OK, RESULT_ERR], &[]];
 
 /// Creates a host with the hvm-core primitive definitions built-in.
 /// This needs the book as an Arc because the closure that logs
diff --git a/src/lib.rs b/src/lib.rs
index c962e9f53..c87b31e2f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,7 +1,7 @@
 #![feature(box_patterns)]
 #![feature(let_chains)]
 
-use builtins::create_host;
+use builtins::{create_host, CORE_BUILTINS_USES};
 use diagnostics::{DiagnosticOrigin, Diagnostics, DiagnosticsConfig, Severity};
 use hvmc::{
   ast::Net,
@@ -63,7 +63,10 @@ pub fn compile_book(
     diagnostics.fatal(())?;
   }
   if opts.prune {
-    core_book.prune(&[book.hvmc_entrypoint().to_string()]);
+    let mut prune_entrypoints = vec![book.hvmc_entrypoint().to_string()];
+    let mut builtin_uses = CORE_BUILTINS_USES.concat().iter().map(|x| x.to_string()).collect::<Vec<_>>();
+    prune_entrypoints.append(&mut builtin_uses);
+    core_book.prune(&prune_entrypoints);
   }
   mutual_recursion::check_cycles(&core_book, &mut diagnostics)?;
 
diff --git a/tests/golden_tests.rs b/tests/golden_tests.rs
index 2d8196c2b..0e538dfba 100644
--- a/tests/golden_tests.rs
+++ b/tests/golden_tests.rs
@@ -357,3 +357,27 @@ fn mutual_recursion() {
     Ok(format!("{}{}", res.diagnostics, res.core_book))
   })
 }
+
+#[test]
+fn io() {
+  run_golden_test_dir_multiple(function_name!(), &[
+    (&|code, path| {
+      let book = do_parse_book(code, path)?;
+
+      let mut desugar_opts = CompileOpts::light();
+      desugar_opts.lazy_mode();
+
+      // 1 million nodes for the test runtime. Smaller doesn't seem to make it any faster
+      let (res, info) =
+        run_book(book, None, RunOpts::lazy(), desugar_opts, DiagnosticsConfig::default(), None)?;
+      Ok(format!("Lazy mode:\n{}{}", info.diagnostics, res))
+    }),
+    (&|code, path| {
+      let book = do_parse_book(code, path)?;
+
+      let (res, info) =
+        run_book(book, None, RunOpts::default(), CompileOpts::light(), DiagnosticsConfig::default(), None)?;
+      Ok(format!("Strict mode:\n{}{}", info.diagnostics, res))
+    }),
+  ])
+}
diff --git a/tests/golden_tests/io/load.hvm b/tests/golden_tests/io/load.hvm
new file mode 100644
index 000000000..2deeb3931
--- /dev/null
+++ b/tests/golden_tests/io/load.hvm
@@ -0,0 +1,6 @@
+(Main) =
+  use path = "tests/golden_tests/io/load.txt"
+  (HVM.load path @result match result {
+    Result.ok: result.val;
+    Result.err: result.val;
+  })
diff --git a/tests/golden_tests/io/load.txt b/tests/golden_tests/io/load.txt
new file mode 100644
index 000000000..dfe437bde
--- /dev/null
+++ b/tests/golden_tests/io/load.txt
@@ -0,0 +1 @@
+Contents
diff --git a/tests/golden_tests/io/load_fail.hvm b/tests/golden_tests/io/load_fail.hvm
new file mode 100644
index 000000000..734831453
--- /dev/null
+++ b/tests/golden_tests/io/load_fail.hvm
@@ -0,0 +1,6 @@
+(Main) =
+  use path = "tests/golden_tests/io/load_fail.txt"
+  (HVM.load path @result match result {
+    Result.ok: result.val;
+    Result.err: result.val;
+  })
diff --git a/tests/golden_tests/io/store.hvm b/tests/golden_tests/io/store.hvm
new file mode 100644
index 000000000..1b6b47174
--- /dev/null
+++ b/tests/golden_tests/io/store.hvm
@@ -0,0 +1,6 @@
+(Main) =
+  use path = "tests/golden_tests/io/store.txt"
+  (HVM.store path "(Main) = 0" @result match result {
+    Result.ok: result.val;
+    Result.err: result.val;
+  })
diff --git a/tests/golden_tests/io/store.txt b/tests/golden_tests/io/store.txt
new file mode 100644
index 000000000..475ff38f2
--- /dev/null
+++ b/tests/golden_tests/io/store.txt
@@ -0,0 +1 @@
+(Main) = 0
\ No newline at end of file
diff --git a/tests/golden_tests/io/store_fail.hvm b/tests/golden_tests/io/store_fail.hvm
new file mode 100644
index 000000000..b6cc8abb8
--- /dev/null
+++ b/tests/golden_tests/io/store_fail.hvm
@@ -0,0 +1,6 @@
+(Main) =
+  use path = "tests/golden_tests/io/missing_dir/store_fail.txt"
+  (HVM.store path "(Main) = 0" @result match result {
+    Result.ok: result.val;
+    Result.err: result.val;
+  })
diff --git a/tests/snapshots/io__load.hvm.snap b/tests/snapshots/io__load.hvm.snap
new file mode 100644
index 000000000..5db3c9ff7
--- /dev/null
+++ b/tests/snapshots/io__load.hvm.snap
@@ -0,0 +1,8 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/io/load.hvm
+---
+Lazy mode:
+"Contents\n"
+Strict mode:
+"Contents\n"
diff --git a/tests/snapshots/io__load_fail.hvm.snap b/tests/snapshots/io__load_fail.hvm.snap
new file mode 100644
index 000000000..f8bedf75d
--- /dev/null
+++ b/tests/snapshots/io__load_fail.hvm.snap
@@ -0,0 +1,8 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/io/load_fail.hvm
+---
+Lazy mode:
+"Filesystem error: No such file or directory (os error 2)"
+Strict mode:
+"Filesystem error: No such file or directory (os error 2)"
diff --git a/tests/snapshots/io__store.hvm.snap b/tests/snapshots/io__store.hvm.snap
new file mode 100644
index 000000000..69efd2406
--- /dev/null
+++ b/tests/snapshots/io__store.hvm.snap
@@ -0,0 +1,8 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/io/store.hvm
+---
+Lazy mode:
+*
+Strict mode:
+*
diff --git a/tests/snapshots/io__store_fail.hvm.snap b/tests/snapshots/io__store_fail.hvm.snap
new file mode 100644
index 000000000..5d2288990
--- /dev/null
+++ b/tests/snapshots/io__store_fail.hvm.snap
@@ -0,0 +1,8 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/io/store_fail.hvm
+---
+Lazy mode:
+"Filesystem error: No such file or directory (os error 2)"
+Strict mode:
+"Filesystem error: No such file or directory (os error 2)"