generate signature for foreign symbols

examples/effect/Effect.roc

@@ -3,4 +3,4 @@ platform folkertdev/foo
     requires [ main ]
     imports []
     effects
-        { putChar Int -> Effect {} }
+        { putChar Int -> Effect {}, putLine Str -> Effect {} }

examples/effect/Main.roc

@@ -2,7 +2,8 @@ app Main provides [ main ] imports [ Effect ]
 
 main : Effect.Effect {} as Fx
 main =
-    e = Effect.putChar 69
-    d = Effect.putChar 68
-    
-    e |> Effect.after \{} -> d
+
+    Effect.putLine "Hello"
+        |> Effect.after \{} -> Effect.putChar 87
+        # |> Effect.after \{} -> Effect.putLine "orld"
+

examples/effect/platform/src/lib.rs

@@ -1,5 +1,6 @@
 use roc_std::alloca;
 use roc_std::RocCallResult;
+use roc_std::RocStr;
 use std::alloc::Layout;
 use std::time::SystemTime;
 
@@ -25,6 +26,15 @@ pub fn roc_fx_putChar(foo: i64) -> () {
     ()
 }
 
+#[no_mangle]
+pub fn roc_fx_putLine(line: RocStr) -> () {
+    let bytes = line.as_slice();
+    let string = unsafe { std::str::from_utf8_unchecked(bytes) };
+    println!("{}", string);
+
+    ()
+}
+
 unsafe fn call_the_closure(function_pointer: *const u8, closure_data_ptr: *const u8) -> i64 {
     let size = size_Fx() as usize;