Merge pull request #158 from Nadrieril/hash

Implement semantic hashing (but no caching yet)

1 files changed, 8 insertions, 0 deletions

diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index 6ba6649..9e935dc 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -1,5 +1,6 @@
 use std::collections::BTreeMap;
 
+use crate::error::Error;
 use crate::semantics::Universe;
 use crate::syntax::map::{DupTreeMap, DupTreeSet};
 use crate::syntax::visitor;
@@ -255,6 +256,13 @@ impl Expr {
             span,
         }
     }
+
+    // Compute the sha256 hash of the binary form of the expression.
+    pub fn hash(&self) -> Result<Box<[u8]>, Error> {
+        use sha2::Digest;
+        let data = binary::encode(self)?;
+        Ok(sha2::Sha256::digest(&data).as_slice().into())
+    }
 }
 
 // Empty enum to indicate that no error can occur