Move generic circuit gadgets into bellman

bellman/src/gadgets.rs

@@ -0,0 +1,33 @@
+pub mod test;
+
+pub mod boolean;
+pub mod multieq;
+pub mod uint32;
+pub mod blake2s;
+pub mod num;
+pub mod lookup;
+pub mod multipack;
+pub mod sha256;
+
+use crate::{
+    SynthesisError
+};
+
+// TODO: This should probably be removed and we
+// should use existing helper methods on `Option`
+// for mapping with an error.
+/// This basically is just an extension to `Option`
+/// which allows for a convenient mapping to an
+/// error on `None`.
+pub trait Assignment<T> {
+    fn get(&self) -> Result<&T, SynthesisError>;
+}
+
+impl<T> Assignment<T> for Option<T> {
+    fn get(&self) -> Result<&T, SynthesisError> {
+        match *self {
+            Some(ref v) => Ok(v),
+            None => Err(SynthesisError::AssignmentMissing)
+        }
+    }
+}