diff --git a/Makefile b/Makefile
index a5c2101..6c29a0b 100644
--- a/Makefile
+++ b/Makefile
@@ -7,6 +7,7 @@ OPT_FLAGS_RUST?= -C target-cpu=native
 OPT_FLAGS?= -march=native -fgraphite -fopenmp -floop-parallelize-all -ftree-parallelize-loops=4 \
 	    -floop-interchange -ftree-loop-distribution -floop-strip-mine -floop-block
 
+FEAT_RUST?= threads
 FEAT_CFLAGS?= -D_RUN_THREADED=0
 FEAT_LDFLAGS?= -lpthread
 
@@ -40,6 +41,9 @@ debug: | dirs $(PROJECT)-debug
 .PHONY: pgo
 pgo: | dirs $(PROJECT)-pgo
 
+.PHONY: rs
+rs: | $(PROJECT)-rs
+
 dirs:
 	@mkdir -p {obj,prof}/src
 
@@ -60,6 +64,11 @@ $(PROJECT)-debug: LDFLAGS := $(DEBUG_LDFLAGS) $(LDFLAGS)
 $(PROJECT)-debug: $(OBJ)
 	$(CC) $^ $(CFLAGS) -o $@ $(LDFLAGS)
 
+
+$(PROJECT)-rs:
+	cd fcmprs && OPT_FLAGS="$(OPT_FLAGS_RUST)" CARGO_FEATURES="$(FEAT_RUST)" $(MAKE)
+	cp -f ./fcmprs/target/release/fcmprs $@
+
 pgo-generate: CFLAGS := $(RELEASE_CFLAGS) $(CFLAGS)
 pgo-generate: LDFLAGS := $(RELEASE_LDFLAGS) $(LDFLAGS)
 pgo-generate: $(PGO_OBJ)
@@ -107,6 +116,9 @@ $(PROJECT)-pgo: pgo-profile
 	mv pgo-use $@
 	strip $@
 
+
+
 clean:
+	cd fcmp && make clean
 	rm -rf {obj,prof}
-	rm -f $(PROJECT)-{release,debug,pgo}
+	rm -f $(PROJECT)-{release,debug,pgo,rs}
diff --git a/fcmprs/Cargo.toml b/fcmprs/Cargo.toml
index 905a6bb..7cf524d 100644
--- a/fcmprs/Cargo.toml
+++ b/fcmprs/Cargo.toml
@@ -20,5 +20,6 @@ panic = "abort"
 [dependencies]
 cfg-if = "1.0.0"
 memmap = "0.7.0"
+once_cell = "1.5.2"
 rayon = {version = "1.5.0", optional = true}
 smallvec = "1.5.0"
diff --git a/fcmprs/src/main.rs b/fcmprs/src/main.rs
index 3d04ead..e95b6da 100644
--- a/fcmprs/src/main.rs
+++ b/fcmprs/src/main.rs
@@ -1,3 +1,6 @@
+
+#![allow(dead_code)]
+
 #[cfg(feature="threads")] use rayon::prelude::*;
 use std::{
     path::Path,
@@ -18,9 +21,25 @@ mod error;
 use error::ResultPrintExt as _;
 
 mod map;
+use map::MappedFile as _;
 
+#[derive(Debug)]
+/// There was a non-matching file
 struct UnmatchError;
 
+const _:() = {
+    use std::{fmt,error};
+    impl error::Error for UnmatchError{}
+    impl fmt::Display for UnmatchError
+    {
+	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+	{
+	    write!(f, "files did not match")
+	}
+    }
+    ()
+};
+
 fn main() {
     let (map1, rest) = {	
 	let mut args = std::env::args().skip(1);
@@ -39,10 +58,9 @@ fn main() {
 		let path = Path::new(&filename);
 		if path.exists() && path.is_file() {
 		    map::map(path).discard_msg(format!("Failed to map file {}", filename))
-			.or_else(|| { ok = false; None })
 		} else {
 		    eprintln!("File {} does not exist or is not a normal file", filename);
-		    ok = false;
+		    ok=false;
 		    None
 		}
 	    }).collect();
@@ -57,7 +75,7 @@ fn main() {
 			    .map(|map| {
 				if slice == map.as_slice() {
 				    Ok(())
-				}else{
+				} else {
 				    Err(UnmatchError)
 				}
 			    })
diff --git a/fcmprs/src/map.rs b/fcmprs/src/map.rs
index 6e8e5c6..5e83582 100644
--- a/fcmprs/src/map.rs
+++ b/fcmprs/src/map.rs
@@ -1,5 +1,26 @@
 use super::*;
 
+use once_cell::sync::OnceCell;
+
+pub trait MappedFile
+{
+    #[inline] fn as_slice(&self) -> &[u8]
+    {
+	&self.as_map()[..]
+    }
+    fn as_map(&self) -> &memmap::Mmap;
+    fn as_file(&self) -> &fs::File;
+}
+
+pub trait MappedFileNew: MappedFile + Sized
+{
+    fn try_map(file: fs::File) -> io::Result<Self>;
+    #[inline] fn map(file: fs::File) -> Self
+    {
+	Self::try_map(file).unwrap()
+    }
+}
+
 /// Represents an open and memory mapped file
 #[derive(Debug)]
 pub struct MemMap
@@ -8,23 +29,107 @@ pub struct MemMap
     file: fs::File,
 }
 
-impl MemMap
+impl MappedFile for MemMap
 {
     /// Get the memory mapped portion as a slice
-    #[inline] pub fn as_slice(&self) -> &[u8]
-    {
+    fn as_slice(&self) -> &[u8] {
 	&self.map[..]
     }
+    fn as_map(&self) -> &memmap::Mmap {
+	&self.map
+    }
+    #[inline] fn as_file(&self) -> &fs::File {
+	&self.file
+    }
+}
+impl MappedFileNew for MemMap
+{
+    #[inline] fn try_map(file: fs::File) -> io::Result<Self>
+    {
+	Ok(MemMap {
+	    map: unsafe { memmap::Mmap::map(&file)? },
+	    file,
+	})
+    }
 }
 
 /// Attempt to map this file
-pub fn map(file: impl AsRef<Path>) -> io::Result<MemMap>
+pub fn map_with<M: MappedFileNew>(file: &Path) -> io::Result<M>
 {
     let file = OpenOptions::new()
         .read(true)
         .open(file)?;
-    Ok(MemMap {
-	map: unsafe { memmap::Mmap::map(&file)? },
-	file,
-    })
+
+    M::try_map(file)
+}
+
+/// Type container for memory map
+pub type DefaultMapType = LazyMap;
+
+/// Attempt to map this file to the `DefaultMapType`
+pub fn map(file: impl AsRef<Path>) -> io::Result<DefaultMapType>
+{
+    map_with(file.as_ref())
+}
+
+/// An open and maybe mapped file
+#[derive(Debug)]
+pub struct LazyMap
+{
+    map: OnceCell<memmap::Mmap>,
+    file: fs::File,
+}
+
+impl LazyMap
+{
+    #[inline(always)] fn get_map(&self) -> &memmap::Mmap
+    {
+	self.map.get_or_init(|| unsafe {memmap::Mmap::map(&self.file).expect("Lazy map failed")})
+    }
+    
+    #[inline(always)] fn try_get_map(&self) -> io::Result<&memmap::Mmap>
+    {
+	self.map.get_or_try_init(|| unsafe {memmap::Mmap::map(&self.file)})
+    }
+    
+    /// Is the memory mapped already?
+    #[inline] pub fn is_mapped(&self) -> bool
+    {
+	self.map.get().is_some()
+    }
+
+    /// Get the mapped portion if it is mapped, attempting a map if not
+    #[inline] pub fn try_as_slice(&self) -> io::Result<&[u8]>
+    {
+	Ok(&self.try_get_map()?[..])
+    }
+}
+
+impl MappedFile for LazyMap
+{
+    /// Get the memory mapped portion as a slice
+    ///
+    /// Returns blank slice if mapping fails
+    #[inline] fn as_slice(&self) -> &[u8]
+    {
+	self.try_get_map()
+	    .map(|x| &x[..])
+	    .unwrap_or(&[])
+    }
+    fn as_map(&self) -> &memmap::Mmap {
+	self.map.get().unwrap()
+    }
+    #[inline] fn as_file(&self) -> &fs::File {
+	&self.file
+    }
+}
+impl MappedFileNew for LazyMap
+{
+    #[inline] fn try_map(file: fs::File) -> io::Result<Self>
+    {
+	Ok(LazyMap {
+	    map: OnceCell::new(),
+	    file,
+	})
+    }
 }