add Haskell to Rust example

haskell-to-rust/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "haskell-to-rust"
+version = "0.1.0"
+authors = ["Bill Murphy <billpmurphy92@gmail.com>"]
+
+[lib]
+name = "double_input"
+crate-type = ["dylib"]

haskell-to-rust/Makefile

@@ -0,0 +1,15 @@
+ifeq ($(shell uname),Darwin)
+	EXT := dylib
+else
+	EXT := so
+endif
+
+all: target/debug/libdouble_input.$(EXT)
+	ghc src/Main.hs target/debug/libdouble_input.$(EXT) -o main
+
+target/debug/libdouble_input.$(EXT): src/lib.rs Cargo.toml
+	cargo build
+
+clean:
+	rm -rf target
+	rm src/*.o src/*.hi

haskell-to-rust/src/Main.hs

@@ -0,0 +1,10 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+
+import Foreign.C
+
+foreign import ccall "double_input" doubleInput :: CInt -> CInt
+
+main = do
+    let input = 4
+    let output = doubleInput input
+    putStrLn $ show input ++ " * 2 = " ++ show output

haskell-to-rust/src/lib.rs

@@ -0,0 +1,4 @@
+#[no_mangle]
+pub extern fn double_input(input: i32) -> i32 {
+        input * 2
+}