diff --git a/ykpack/src/lib.rs b/ykpack/src/lib.rs
index 89e9a50ab..9e315e784 100644
--- a/ykpack/src/lib.rs
+++ b/ykpack/src/lib.rs
@@ -41,7 +41,8 @@ pub use types::*;
 #[cfg(test)]
 mod tests {
     use super::{
-        BasicBlock, Decoder, DefId, Encoder, Mir, Pack, Place, Rvalue, Statement, Terminator,
+        BasicBlock, Decoder, DefId, Encoder, Mir, Operand, Pack, Place, PlaceBase, Rvalue,
+        Statement, Terminator,
     };
     use fallible_iterator::{self, FallibleIterator};
     use std::io::{Cursor, Seek, SeekFrom};
@@ -137,10 +138,13 @@ mod tests {
     fn test_text_dump() {
         let stmts_t1_b0 = vec![
             Statement::Nop,
-            Statement::Assign(Place::Local(42), Rvalue::Place(Place::Local(43))),
             Statement::Assign(
-                Place::Local(44),
-                Rvalue::Phi(vec![Place::Local(100), Place::Local(200)]),
+                Place::Base(PlaceBase::Local(42)),
+                Rvalue::Use(Operand::Place(Place::Base(PlaceBase::Local(43)))),
+            ),
+            Statement::Assign(
+                Place::Base(PlaceBase::Local(44)),
+                Rvalue::Use(Operand::Place(Place::Base(PlaceBase::Local(300)))),
             ),
         ];
         let term_t1_b0 = Terminator::Abort;
@@ -168,21 +172,21 @@ mod tests {
         let got_lines = got.split("\n");
 
         let expect = "[Begin TIR for item1]\n\
-	    DefId(1, 2):
-	    bb0:
-		Nop
-		Assign(Local(42), Place(Local(43)))
-		Assign(Local(44), Phi([Local(100), Local(200)]))
-		term: Abort
-
-	    bb1:
-		Unimplemented
-		term: Goto { target_bb: 50 }
-
-	[End TIR for item1]
-	[Begin TIR for item2]
-	    DefId(3, 4):
-	[End TIR for item2]\n";
+            DefId(1, 2):
+            bb0:
+                Nop
+                Assign(Base(Local(42)), Use(Place(Base(Local(43)))))
+                Assign(Base(Local(44)), Use(Place(Base(Local(300)))))
+                term: Abort
+
+            bb1:
+                Unimplemented
+                term: Goto { target_bb: 50 }
+
+        [End TIR for item1]
+        [Begin TIR for item2]
+            DefId(3, 4):
+        [End TIR for item2]\n";
 
         let expect_lines = expect.split("\n");
 
diff --git a/ykpack/src/types.rs b/ykpack/src/types.rs
index 2b05d48dd..5be4d3b84 100644
--- a/ykpack/src/types.rs
+++ b/ykpack/src/types.rs
@@ -10,12 +10,17 @@
 //! Types for the Yorick intermediate language.
 
 use serde::{Deserialize, Serialize};
-use std::fmt::{self, Display};
+use std::{
+    fmt::{self, Display},
+    marker::PhantomData,
+};
 
 pub type CrateHash = u64;
 pub type DefIndex = u32;
 pub type BasicBlockIndex = u32;
 pub type LocalIndex = u32;
+pub type VariantIndex = u32;
+pub type PromotedIndex = u32;
 
 /// A mirror of the compiler's notion of a "definition ID".
 #[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
@@ -93,7 +98,8 @@ impl Display for BasicBlock {
 pub enum Statement {
     Nop,
     Assign(Place, Rvalue),
-    Unimplemented, // FIXME
+    SetDiscriminant(Place, VariantIndex),
+    Unimplemented,
 }
 
 impl Display for Statement {
@@ -102,19 +108,112 @@ impl Display for Statement {
     }
 }
 
+/// A place for storing things.
 #[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
 pub enum Place {
+    Base(PlaceBase),
+    Projection(PlaceProjection),
+}
+
+/// The "base" of a place projection.
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum PlaceBase {
     Local(LocalIndex),
-    Unimplemented, // FIXME
+    Static(DefId),
+    Promoted(PromotedIndex),
 }
 
+/// A projection (deref, index, field access, ...).
 #[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
-pub enum Rvalue {
+pub struct PlaceProjection {
+    pub base: Box<Place>,
+    pub elem: ProjectionElem<LocalIndex>,
+}
+
+/// Describes a projection operation upon a projection base.
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum ProjectionElem<V> {
+    Unimplemented(PhantomData<V>), // FIXME
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum Operand {
+    /// In MIR this is either Move or Copy.
     Place(Place),
-    Phi(Vec<Place>),
+    Unimplemented, // FIXME constants
+}
+
+/// Borrow descriptions.
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum BorrowKind {
+    Shared,
+    Shallow,
+    Unique,
+    Mut, // FIXME two_phase borrow.
+}
+
+/// Things that can appear on the right-hand side of an assignment.
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum Rvalue {
+    Use(Operand),
+    Repeat(Operand, u64),
+    Ref(BorrowKind, Place), // We do not store the region.
+    Len(Place),
+    BinaryOp(BinOp, Operand, Operand),
+    CheckedBinaryOp(BinOp, Operand, Operand),
+    NullaryOp(NullOp),
+    UnaryOp(UnOp, Operand),
+    Discriminant(Place),
+    Aggregate(AggregateKind, Vec<Operand>),
     Unimplemented, // FIXME
 }
 
+/// Kinds of aggregate types.
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum AggregateKind {
+    Array,
+    Tuple,
+    Closure(DefId),
+    Generator(DefId),
+    Unimplemented,
+}
+
+/// Binary operations.
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum BinOp {
+    Add,
+    Sub,
+    Mul,
+    Div,
+    Rem,
+    BitXor,
+    BitAnd,
+    BitOr,
+    Shl,
+    Shr,
+    Eq,
+    Lt,
+    Le,
+    Ne,
+    Ge,
+    Gt,
+    Offset,
+}
+
+// Operations with no arguments.
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum NullOp {
+    SizeOf,
+    Box,
+}
+
+// Unary operations.
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum UnOp {
+    Not,
+    Neg,
+}
+
 /// A call target.
 #[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
 pub enum CallOperand {