diff --git a/src/lib.rs b/src/lib.rs
index e5ac623..a551146 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,37 +1,69 @@
-use std::env;
+use std::{env, fmt, result};
 use std::process::exit;
 use std::error::Error;
 use std::path::PathBuf;
 use std::fs::File;
-use std::io::{Write, BufRead, BufReader};
+use std::io::{self, Write, BufRead, BufReader};
 
 use colored::*;
 
-pub fn git_dir() -> String {
-    match env::var("GCLONE_PATH") {
-        Ok(path) => path,
-        Err(e) => {
-            eprintln!("{} {} {}",
-                "error:".bold().red(),
-                "environment variable GCLONE_PATH must be set:".bold(),
-                e.description());
-
-            exit(1);
-        },
+macro_rules! impl_from_error {
+    ($type: ty, $variant: path, $from: ty) => {
+        impl From<$from> for $type {
+            fn from(e: $from) -> $type {
+                $variant(e)
+            }
+        }
     }
 }
 
+#[derive(Debug)]
+pub enum MError {
+    NoGclonePath(env::VarError),
+    IoError(io::Error),
+}
+
+impl_from_error!(MError, MError::NoGclonePath, env::VarError);
+impl_from_error!(MError, MError::IoError, io::Error);
+
+impl fmt::Display for MError {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            MError::NoGclonePath(e) =>
+                write!(fmt, "{} {} {}",
+                    "error:".bold().red(),
+                    "couldn't read environment variable GCLONE_PATH".bold(),
+                    e),
+            MError::IoError(e) =>
+                write!(fmt, "{} {} {}",
+                    "error:".bold().red(),
+                    "couldn't read or write cache:".bold(),
+                    e),
+        }
+    }
+}
+
+impl Error for MError {
+
+}
+
+type Result<T> = result::Result<T, MError>;
+
+pub fn git_dir() -> Result<String> {
+    Ok(env::var("GCLONE_PATH")?)
+}
+
 pub struct Cache(Vec<String>);
 
 impl Cache {
-    pub fn read() -> Cache {
+    pub fn read() -> Result<Cache> {
 
-        let mut path = PathBuf::from(git_dir());
+        let mut path = PathBuf::from(git_dir()?);
         path.push(".cdgcache");
 
         let file = match File::open(&path) {
             Ok(f) => f,
-            Err(_) => return Cache(vec![]),
+            Err(_) => return Ok(Cache(vec![])),
         };
 
         let file = BufReader::new(file);
@@ -44,11 +76,11 @@ impl Cache {
             }
         }
 
-        Cache(values)
+        Ok(Cache(values))
     }
 
-    pub fn write(&self) -> Result<(), Box<Error>> {
-        let mut path = PathBuf::from(git_dir());
+    pub fn write(&self) -> Result<()> {
+        let mut path = PathBuf::from(git_dir()?);
         path.push(".cdgcache");
         let mut file = File::create(path)?;