diff --git a/tamer/src/asg/graph.rs b/tamer/src/asg/graph.rs
index 62bd7c36..c1de4c4f 100644
--- a/tamer/src/asg/graph.rs
+++ b/tamer/src/asg/graph.rs
@@ -211,8 +211,8 @@ impl Asg {
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
     ) -> Result<(), AsgError> {
-        from_oi.pre_add_edge(self, to_oi, ctx_span, |asg| {
-            asg.graph.add_edge(
+        from_oi.pre_add_edge(self, to_oi, ctx_span).map(|()| {
+            self.graph.add_edge(
                 from_oi.widen().into(),
                 to_oi.into(),
                 (from_oi.src_rel_ty(), OB::rel_ty(), ctx_span),
@@ -511,14 +511,11 @@ pub trait AsgRelMut<OB: ObjectRelatable>: ObjectRelatable {
     ///   type for you.
     fn pre_add_edge(
         asg: &mut Asg,
-        _from_oi: ObjectIndex<Self>,
-        _to_oi: ObjectIndex<OB>,
-        _ctx_span: Option<Span>,
-        commit: impl FnOnce(&mut Asg),
+        rel: ProposedRel<Self, OB>,
     ) -> Result<(), AsgError>;
 }
 
-impl<O: ObjectRelatable, OB: ObjectRelatable> AsgRelMut<OB> for O {
+impl<OA: ObjectRelatable, OB: ObjectRelatable> AsgRelMut<OB> for OA {
     /// Default edge creation method for all [`ObjectKind`]s.
     ///
     /// This takes the place of a default implementation on the trait itself
@@ -531,15 +528,21 @@ impl<O: ObjectRelatable, OB: ObjectRelatable> AsgRelMut<OB> for O {
     ///     overridden for a particular edge for a particular object
     ///       (see [`object::tpl`] as an example).
     default fn pre_add_edge(
-        asg: &mut Asg,
-        _from_oi: ObjectIndex<O>,
-        _to_oi: ObjectIndex<OB>,
-        _ctx_span: Option<Span>,
-        commit: impl FnOnce(&mut Asg),
+        _asg: &mut Asg,
+        _rel: ProposedRel<Self, OB>,
     ) -> Result<(), AsgError> {
-        Ok(commit(asg))
+        let _ = _rel.ctx_span; // TODO: remove when used (dead_code)
+        Ok(())
     }
 }
 
+/// The relationship proposed by [`Asg::add_edge`],
+///   requiring approval from [`AsgRelMut::pre_add_edge`].
+pub struct ProposedRel<OA: ObjectKind, OB: ObjectKind> {
+    from_oi: ObjectIndex<OA>,
+    to_oi: ObjectIndex<OB>,
+    ctx_span: Option<Span>,
+}
+
 #[cfg(test)]
 mod test;
diff --git a/tamer/src/asg/graph/object/rel.rs b/tamer/src/asg/graph/object/rel.rs
index 41a7b2a8..de58be0b 100644
--- a/tamer/src/asg/graph/object/rel.rs
+++ b/tamer/src/asg/graph/object/rel.rs
@@ -27,7 +27,7 @@ use super::{
 };
 use crate::{
     asg::{
-        graph::{object::Tpl, AsgRelMut},
+        graph::{object::Tpl, AsgRelMut, ProposedRel},
         Asg, AsgError,
     },
     f::Map,
@@ -864,7 +864,6 @@ pub trait ObjectIndexRelTo<OB: ObjectRelatable>: Sized + Clone + Copy {
         asg: &mut Asg,
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
-        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError>;
 
     /// Check whether an edge exists from `self` to `to_oi`.
@@ -948,14 +947,14 @@ where
         asg: &mut Asg,
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
-        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError> {
         O::pre_add_edge(
             asg,
-            self.widen().must_narrow_into::<O>(),
-            to_oi,
-            ctx_span,
-            commit,
+            ProposedRel {
+                from_oi: self.widen().must_narrow_into::<O>(),
+                to_oi,
+                ctx_span,
+            },
         )
     }
 }
@@ -976,16 +975,16 @@ impl<OB: ObjectRelatable> ObjectIndexRelTo<OB> for ObjectIndexTo<OB> {
         asg: &mut Asg,
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
-        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError> {
         macro_rules! pre_add_edge {
             ($ty:ident) => {
                 $ty::pre_add_edge(
                     asg,
-                    self.widen().must_narrow_into::<$ty>(),
-                    to_oi,
-                    ctx_span,
-                    commit,
+                    ProposedRel {
+                        from_oi: self.widen().must_narrow_into::<$ty>(),
+                        to_oi,
+                        ctx_span,
+                    },
                 )
             };
         }
@@ -1020,10 +1019,9 @@ impl<OB: ObjectRelatable> ObjectIndexRelTo<OB> for ObjectIndexToTree<OB> {
         asg: &mut Asg,
         to_oi: ObjectIndex<OB>,
         ctx_span: Option<Span>,
-        commit: impl FnOnce(&mut Asg),
     ) -> Result<(), AsgError> {
         match self {
-            Self(oito) => oito.pre_add_edge(asg, to_oi, ctx_span, commit),
+            Self(oito) => oito.pre_add_edge(asg, to_oi, ctx_span),
         }
     }
 }
diff --git a/tamer/src/asg/graph/object/tpl.rs b/tamer/src/asg/graph/object/tpl.rs
index a1870e84..aa3f3f87 100644
--- a/tamer/src/asg/graph/object/tpl.rs
+++ b/tamer/src/asg/graph/object/tpl.rs
@@ -22,7 +22,7 @@
 use std::fmt::Display;
 
 use super::{prelude::*, Doc, Expr, Ident};
-use crate::{f::Map, parse::util::SPair, span::Span};
+use crate::{asg::graph::ProposedRel, f::Map, parse::util::SPair, span::Span};
 
 /// Template with associated name.
 #[derive(Debug, PartialEq, Eq)]
@@ -220,20 +220,15 @@ object_rel! {
         tree Expr {
             fn pre_add_edge(
                 asg: &mut Asg,
-                from_oi: ObjectIndex<Self>,
-                to_oi: ObjectIndex<Expr>,
-                _ctx_span: Option<Span>,
-                commit: impl FnOnce(&mut Asg),
+                rel: ProposedRel<Self, Expr>,
             ) -> Result<(), AsgError> {
-                let tpl_name = from_oi.name(asg);
-                let span = to_oi.resolve(asg).span();
+                let tpl_name = rel.from_oi.name(asg);
+                let span = rel.to_oi.resolve(asg).span();
 
-                from_oi.try_map_obj_inner(
+                rel.from_oi.try_map_obj_inner(
                     asg,
                     try_adapt_to(TplShape::Expr(span), tpl_name),
-                )?;
-
-                Ok(commit(asg))
+                ).map(|_| ())
             }
         },
 
@@ -245,23 +240,18 @@ object_rel! {
         tree Tpl {
             fn pre_add_edge(
                 asg: &mut Asg,
-                from_oi: ObjectIndex<Self>,
-                to_oi: ObjectIndex<Tpl>,
-                _ctx_span: Option<Span>,
-                commit: impl FnOnce(&mut Asg),
+                rel: ProposedRel<Self, Tpl>,
             ) -> Result<(), AsgError> {
-                let tpl_name = from_oi.name(asg);
-                let apply = to_oi.resolve(asg);
+                let tpl_name = rel.from_oi.name(asg);
+                let apply = rel.to_oi.resolve(asg);
                 let apply_shape = apply
                     .shape()
                     .overwrite_span_if_any(apply.span());
 
-                from_oi.try_map_obj_inner(
+                rel.from_oi.try_map_obj_inner(
                     asg,
                     try_adapt_to(apply_shape, tpl_name),
-                )?;
-
-                Ok(commit(asg))
+                ).map(|_| ())
             }
         },