diff --git a/compiler/forget/src/HIR/BuildHIR.ts b/compiler/forget/src/HIR/BuildHIR.ts
index fff2abe47a..9ed27aab02 100644
--- a/compiler/forget/src/HIR/BuildHIR.ts
+++ b/compiler/forget/src/HIR/BuildHIR.ts
@@ -20,7 +20,7 @@ import {
   Terminal,
   ThrowTerminal,
 } from "./HIR";
-import HIRBuilder from "./HIRBuilder";
+import HIRBuilder, { Environment } from "./HIRBuilder";
 import todo, { todoInvariant } from "./todo";
 
 // *******************************************************************************************
@@ -46,8 +46,11 @@ const GLOBALS: Map<string, t.Identifier> = new Map([
  * TODO: consider modeling control-flow at expression level for even more fine-
  * grained reactivity.
  */
-export function lower(func: NodePath<t.Function>): HIRFunction {
-  const builder = new HIRBuilder();
+export function lower(
+  func: NodePath<t.Function>,
+  env: Environment
+): HIRFunction {
+  const builder = new HIRBuilder(env);
 
   const id =
     func.isFunctionDeclaration() && func.node.id != null
diff --git a/compiler/forget/src/HIR/HIR.ts b/compiler/forget/src/HIR/HIR.ts
index c09eef78c5..e1c409beb2 100644
--- a/compiler/forget/src/HIR/HIR.ts
+++ b/compiler/forget/src/HIR/HIR.ts
@@ -292,11 +292,3 @@ export function makeScopeId(id: number): ScopeId {
  */
 const opaqueIdentifierId = Symbol();
 export type IdentifierId = number & { [opaqueIdentifierId]: "IdentifierId" };
-
-export function makeIdentifierId(id: number): IdentifierId {
-  invariant(
-    id >= 0 && Number.isInteger(id),
-    "Expected identifier id to be a non-negative integer"
-  );
-  return id as IdentifierId;
-}
diff --git a/compiler/forget/src/HIR/HIRBuilder.ts b/compiler/forget/src/HIR/HIRBuilder.ts
index 5f754be897..bb198b5620 100644
--- a/compiler/forget/src/HIR/HIRBuilder.ts
+++ b/compiler/forget/src/HIR/HIRBuilder.ts
@@ -16,7 +16,6 @@ import {
   IdentifierId,
   Instruction,
   makeBlockId,
-  makeIdentifierId,
   Terminal,
 } from "./HIR";
 
@@ -56,6 +55,22 @@ function newBlock(id: BlockId): WipBlock {
   return { id, instructions: [] };
 }
 
+export class Environment {
+  #nextIdentifer: number = 0;
+
+  #makeIdentifierId(id: number): IdentifierId {
+    invariant(
+      id >= 0 && Number.isInteger(id),
+      "Expected identifier id to be a non-negative integer"
+    );
+    return id as IdentifierId;
+  }
+
+  get nextIdentifierId(): IdentifierId {
+    return this.#makeIdentifierId(this.#nextIdentifer++);
+  }
+}
+
 /**
  * Helper class for constructing a CFG
  */
@@ -65,8 +80,16 @@ export default class HIRBuilder {
   #current: WipBlock = newBlock(makeBlockId(0));
   #entry: BlockId = makeBlockId(0);
   #scopes: Array<Scope> = [];
-  #nextIdentifier: IdentifierId = makeIdentifierId(0);
   #bindings: Map<t.Identifier, Identifier> = new Map();
+  #env: Environment;
+
+  get nextIdentifierId() {
+    return this.#env.nextIdentifierId;
+  }
+
+  constructor(env: Environment) {
+    this.#env = env;
+  }
 
   debug(): string {
     return JSON.stringify(
@@ -88,7 +111,7 @@ export default class HIRBuilder {
   }
 
   makeTemporary(): Identifier {
-    const id = makeIdentifierId(this.#nextIdentifier++);
+    const id = this.nextIdentifierId;
     return {
       id,
       name: null,
@@ -98,7 +121,7 @@ export default class HIRBuilder {
   resolveIdentifier(node: t.Identifier): Identifier {
     let identifier = this.#bindings.get(node);
     if (identifier == null) {
-      const id = makeIdentifierId(this.#nextIdentifier++);
+      const id = this.nextIdentifierId;
       identifier = { id, name: node.name };
       this.#bindings.set(node, identifier);
     }
diff --git a/compiler/forget/src/HIR/SSAify.ts b/compiler/forget/src/HIR/SSAify.ts
index 422717389f..bb45a0082c 100644
--- a/compiler/forget/src/HIR/SSAify.ts
+++ b/compiler/forget/src/HIR/SSAify.ts
@@ -8,10 +8,10 @@ import {
   IdentifierId,
   Instruction,
   InstructionKind,
-  makeIdentifierId,
   Phi,
   Place,
 } from "./HIR";
+import { Environment } from "./HIRBuilder";
 
 type IncompletePhi = {
   old: Place;
@@ -29,6 +29,15 @@ class SSABuilder {
   #states: Map<BasicBlock, State> = new Map();
   #current: BasicBlock | null = null;
   visitedBlocks: Set<BasicBlock> = new Set();
+  #env: Environment;
+
+  constructor(env: Environment) {
+    this.#env = env;
+  }
+
+  get nextIdentifierId() {
+    return this.#env.nextIdentifierId;
+  }
 
   // Hack(gsn): Start from the last stored id in HIRBuilder.
   // Need to refactor makeTemporary and relevant state out of HIR Builder.
@@ -47,7 +56,7 @@ class SSABuilder {
   makePlace(oldPlace: Place): Place {
     const identifier = {
       ...oldPlace.identifier,
-      id: makeIdentifierId(this.#id++),
+      id: this.nextIdentifierId,
     };
     return {
       ...oldPlace,
@@ -58,7 +67,7 @@ class SSABuilder {
   makePlaceForPhi(oldPlace: Place): Place {
     const identifier = {
       ...oldPlace.identifier,
-      id: makeIdentifierId(this.#id++),
+      id: this.nextIdentifierId,
     };
     return {
       identifier,
@@ -173,9 +182,8 @@ class SSABuilder {
   }
 }
 
-export default function buildSSA(func: HIRFunction) {
-  const builder = new SSABuilder();
-
+export default function buildSSA(func: HIRFunction, env: Environment) {
+  const builder = new SSABuilder(env);
   function visit(blockId: BlockId) {
     const block = func.body.blocks.get(blockId)!;
     if (builder.visitedBlocks.has(block)) {
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md
index 85c2fa2feb..e48c6b6314 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-multiple-if.expect.md
@@ -21,30 +21,30 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
-  Let mutate y$1001 = 2
-  Const mutate $1002 = 2
-  Const mutate $1003 = Binary mutate y$1001 === mutate $1002
-  If (mutate $1003) then:bb2 else:bb1
+  Let mutate x$7 = 1
+  Let mutate y$8 = 2
+  Const mutate $9 = 2
+  Const mutate $10 = Binary mutate y$8 === mutate $9
+  If (mutate $10) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  Reassign mutate x$1011 = 3
+  Reassign mutate x$18 = 3
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb2
-  Const mutate y$1005: phi(bb0: mutate y$1001, bb2: mutate y$1001)
-  Const mutate x$1010: phi(bb0: mutate x$1000, bb2: mutate x$1011)
-  Const mutate $1004 = 3
-  Const mutate $1006 = Binary mutate y$1005 === mutate $1004
-  If (mutate $1006) then:bb4 else:bb3
+  Const mutate y$12: phi(bb0: mutate y$8, bb2: mutate y$8)
+  Const mutate x$17: phi(bb0: mutate x$7, bb2: mutate x$18)
+  Const mutate $11 = 3
+  Const mutate $13 = Binary mutate y$12 === mutate $11
+  If (mutate $13) then:bb4 else:bb3
 bb4:
   predecessor blocks: bb1
-  Reassign mutate x$1009 = 5
+  Reassign mutate x$16 = 5
   Goto bb3
 bb3:
   predecessor blocks: bb1 bb4
-  Const mutate x$1007: phi(bb1: mutate x$1010, bb4: mutate x$1009)
-  Reassign mutate y$1008 = mutate x$1007
+  Const mutate x$14: phi(bb1: mutate x$17, bb4: mutate x$16)
+  Reassign mutate y$15 = mutate x$14
   Return
 ```
 
@@ -52,17 +52,17 @@ bb3:
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
-  let y$1001 = 2;
-  if (y$1001 === 2) {
-    x$1011 = 3;
+  let x$7 = 1;
+  let y$8 = 2;
+  if (y$8 === 2) {
+    x$18 = 3;
     ("<<TODO: handle complex control flow in codegen>>");
   }
-  if (y$1005 === 3) {
-    x$1009 = 5;
+  if (y$12 === 3) {
+    x$16 = 5;
     ("<<TODO: handle complex control flow in codegen>>");
   }
-  y$1008 = x$1007;
+  y$15 = x$14;
   return;
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md
index 23199e29ef..6bbc99b56a 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-complex-single-if.expect.md
@@ -18,19 +18,19 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
-  Let mutate y$1001 = 2
-  Const mutate $1002 = 2
-  Const mutate $1003 = Binary mutate y$1001 === mutate $1002
-  If (mutate $1003) then:bb2 else:bb1
+  Let mutate x$5 = 1
+  Let mutate y$6 = 2
+  Const mutate $7 = 2
+  Const mutate $8 = Binary mutate y$6 === mutate $7
+  If (mutate $8) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  Reassign mutate x$1006 = 3
+  Reassign mutate x$11 = 3
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb2
-  Const mutate x$1004: phi(bb0: mutate x$1000, bb2: mutate x$1006)
-  Reassign mutate y$1005 = mutate x$1004
+  Const mutate x$9: phi(bb0: mutate x$5, bb2: mutate x$11)
+  Reassign mutate y$10 = mutate x$9
   Return
 ```
 
@@ -38,13 +38,13 @@ bb1:
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
-  let y$1001 = 2;
-  if (y$1001 === 2) {
-    x$1006 = 3;
+  let x$5 = 1;
+  let y$6 = 2;
+  if (y$6 === 2) {
+    x$11 = 3;
     ("<<TODO: handle complex control flow in codegen>>");
   }
-  y$1005 = x$1004;
+  y$10 = x$9;
   return;
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md
index aa2598cd18..cf1efa02b0 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-for.expect.md
@@ -16,29 +16,29 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 0
+  Let mutate x$5 = 0
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb4
-  Const mutate x$1002: phi(bb0: mutate x$1000, bb4: mutate x$1005)
-  Const mutate $1001 = 10
-  Const mutate $1003 = Binary mutate x$1002 < mutate $1001
-  If (mutate $1003) then:bb4 else:bb2
+  Const mutate x$7: phi(bb0: mutate x$5, bb4: mutate x$10)
+  Const mutate $6 = 10
+  Const mutate $8 = Binary mutate x$7 < mutate $6
+  If (mutate $8) then:bb4 else:bb2
 bb4:
   predecessor blocks: bb1
-  Const mutate $1004 = 1
-  Reassign mutate x$1005 = Binary mutate x$1002 + mutate $1004
+  Const mutate $9 = 1
+  Reassign mutate x$10 = Binary mutate x$7 + mutate $9
   Goto bb1
 bb2:
   predecessor blocks: bb1
-  Return mutate x$1002
+  Return mutate x$7
 ```
 
 ## Code
 
 ```javascript
 function foo$0() {
-  let x$1000 = 0;
+  let x$5 = 0;
   ("<<TODO: handle complex control flow in codegen>>");
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-if-else.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-if-else.expect.md
index d68255620b..f920361821 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-if-else.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-if-else.expect.md
@@ -19,16 +19,16 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
-  Let mutate y$1001 = 2
-  If (mutate y$1001) then:bb2 else:bb3
+  Let mutate x$5 = 1
+  Let mutate y$6 = 2
+  If (mutate y$6) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
-  Let mutate z$1003 = Binary mutate x$1000 + mutate y$1001
+  Let mutate z$8 = Binary mutate x$5 + mutate y$6
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  Let mutate z$1002 = mutate x$1000
+  Let mutate z$7 = mutate x$5
   Goto bb1
 bb1:
   predecessor blocks: bb3 bb2
@@ -39,13 +39,13 @@ bb1:
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
-  let y$1001 = 2;
-  if (y$1001) {
-    let z$1003 = x$1000 + y$1001;
+  let x$5 = 1;
+  let y$6 = 2;
+  if (y$6) {
+    let z$8 = x$5 + y$6;
     ("<<TODO: handle complex control flow in codegen>>");
   } else {
-    let z$1002 = x$1000;
+    let z$7 = x$5;
     ("<<TODO: handle complex control flow in codegen>>");
   }
   return;
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md
index 45cfc3a2e4..ccb178a710 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-return.expect.md
@@ -17,30 +17,30 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
-  Const mutate $1001 = 1
-  Const mutate $1002 = Binary mutate x$1000 === mutate $1001
-  If (mutate $1002) then:bb2 else:bb1
+  Let mutate x$4 = 1
+  Const mutate $5 = 1
+  Const mutate $6 = Binary mutate x$4 === mutate $5
+  If (mutate $6) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  Reassign mutate x$1004 = 2
+  Reassign mutate x$8 = 2
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb2
-  Const mutate x$1003: phi(bb0: mutate x$1000, bb2: mutate x$1004)
-  Return mutate x$1003
+  Const mutate x$7: phi(bb0: mutate x$4, bb2: mutate x$8)
+  Return mutate x$7
 ```
 
 ## Code
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
-  if (x$1000 === 1) {
-    x$1004 = 2;
+  let x$4 = 1;
+  if (x$4 === 1) {
+    x$8 = 2;
     ("<<TODO: handle complex control flow in codegen>>");
   }
-  return x$1003;
+  return x$7;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md
index da3a8f9d63..3de7aae32b 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple-phi.expect.md
@@ -20,22 +20,22 @@ function foo() {
 
 ```
 bb0:
-  Let mutate y$1000 = 2
-  Const mutate $1001 = 1
-  Const mutate $1002 = Binary mutate y$1000 > mutate $1001
-  If (mutate $1002) then:bb2 else:bb3
+  Let mutate y$5 = 2
+  Const mutate $6 = 1
+  Const mutate $7 = Binary mutate y$5 > mutate $6
+  If (mutate $7) then:bb2 else:bb3
 bb2:
   predecessor blocks: bb0
-  Reassign mutate y$1006 = 1
+  Reassign mutate y$11 = 1
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  Reassign mutate y$1003 = 2
+  Reassign mutate y$8 = 2
   Goto bb1
 bb1:
   predecessor blocks: bb3 bb2
-  Const mutate y$1004: phi(bb3: mutate y$1003, bb2: mutate y$1006)
-  Let mutate x$1005 = mutate y$1004
+  Const mutate y$9: phi(bb3: mutate y$8, bb2: mutate y$11)
+  Let mutate x$10 = mutate y$9
   Return
 ```
 
@@ -43,15 +43,15 @@ bb1:
 
 ```javascript
 function foo$0() {
-  let y$1000 = 2;
-  if (y$1000 > 1) {
-    y$1006 = 1;
+  let y$5 = 2;
+  if (y$5 > 1) {
+    y$11 = 1;
     ("<<TODO: handle complex control flow in codegen>>");
   } else {
-    y$1003 = 2;
+    y$8 = 2;
     ("<<TODO: handle complex control flow in codegen>>");
   }
-  let x$1005 = y$1004;
+  let x$10 = y$9;
   return;
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md
index 104b2a4f7c..5e57e56d29 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-simple.expect.md
@@ -13,8 +13,8 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
-  Let mutate y$1001 = 2
+  Let mutate x$3 = 1
+  Let mutate y$4 = 2
   Return
 ```
 
@@ -22,8 +22,8 @@ bb0:
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
-  let y$1001 = 2;
+  let x$3 = 1;
+  let y$4 = 2;
   return;
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-single-if.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-single-if.expect.md
index 501c07b2d0..aef7fb703d 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-single-if.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-single-if.expect.md
@@ -17,12 +17,12 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
-  Let mutate y$1001 = 2
-  If (mutate y$1001) then:bb2 else:bb1
+  Let mutate x$4 = 1
+  Let mutate y$5 = 2
+  If (mutate y$5) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  Let mutate z$1002 = Binary mutate x$1000 + mutate y$1001
+  Let mutate z$6 = Binary mutate x$4 + mutate y$5
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb2
@@ -33,10 +33,10 @@ bb1:
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
-  let y$1001 = 2;
-  if (y$1001) {
-    let z$1002 = x$1000 + y$1001;
+  let x$4 = 1;
+  let y$5 = 2;
+  if (y$5) {
+    let z$6 = x$4 + y$5;
     ("<<TODO: handle complex control flow in codegen>>");
   }
   return;
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
index 5845ad9436..b4c5033f86 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-switch.expect.md
@@ -28,34 +28,34 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
-  Const mutate $1001 = 2
-  Const mutate $1002 = Binary mutate x$1000 === mutate $1001
-  Const mutate $1003 = 1
-  Const mutate $1004 = Binary mutate x$1000 === mutate $1003
-  Switch (mutate x$1000)
-    Case mutate $1004: bb5
-    Case mutate $1002: bb3
+  Let mutate x$10 = 1
+  Const mutate $11 = 2
+  Const mutate $12 = Binary mutate x$10 === mutate $11
+  Const mutate $13 = 1
+  Const mutate $14 = Binary mutate x$10 === mutate $13
+  Switch (mutate x$10)
+    Case mutate $14: bb5
+    Case mutate $12: bb3
     Default: bb2
 bb5:
   predecessor blocks: bb0
-  Const mutate $1011 = 1
-  Reassign mutate x$1012 = Binary mutate x$1000 + mutate $1011
+  Const mutate $21 = 1
+  Reassign mutate x$22 = Binary mutate x$10 + mutate $21
   Goto bb1
 bb3:
   predecessor blocks: bb0
-  Const mutate $1009 = 2
-  Reassign mutate x$1010 = Binary mutate x$1000 + mutate $1009
+  Const mutate $19 = 2
+  Reassign mutate x$20 = Binary mutate x$10 + mutate $19
   Goto bb1
 bb2:
   predecessor blocks: bb0
-  Const mutate $1005 = 3
-  Reassign mutate x$1006 = Binary mutate x$1000 + mutate $1005
+  Const mutate $15 = 3
+  Reassign mutate x$16 = Binary mutate x$10 + mutate $15
   Goto bb1
 bb1:
   predecessor blocks: bb5 bb3 bb2
-  Const mutate x$1007: phi(bb5: mutate x$1012, bb3: mutate x$1010, bb2: mutate x$1006)
-  Let mutate y$1008 = mutate x$1007
+  Const mutate x$17: phi(bb5: mutate x$22, bb3: mutate x$20, bb2: mutate x$16)
+  Let mutate y$18 = mutate x$17
   Return
 ```
 
@@ -63,22 +63,22 @@ bb1:
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
-  switch (x$1000) {
-    case x$1000 === 1: {
-      x$1012 = x$1000 + 1;
+  let x$10 = 1;
+  switch (x$10) {
+    case x$10 === 1: {
+      x$22 = x$10 + 1;
       ("<<TODO: handle complex control flow in codegen>>");
     }
-    case x$1000 === 2: {
-      x$1010 = x$1000 + 2;
+    case x$10 === 2: {
+      x$20 = x$10 + 2;
       ("<<TODO: handle complex control flow in codegen>>");
     }
     default: {
-      x$1006 = x$1000 + 3;
+      x$16 = x$10 + 3;
       ("<<TODO: handle complex control flow in codegen>>");
     }
   }
-  let y$1008 = x$1007;
+  let y$18 = x$17;
   return;
 }
 
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md
index 39f079b678..833cf61c93 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-throw.expect.md
@@ -16,30 +16,30 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
-  Const mutate $1001 = 1
-  Const mutate $1002 = Binary mutate x$1000 === mutate $1001
-  If (mutate $1002) then:bb2 else:bb1
+  Let mutate x$4 = 1
+  Const mutate $5 = 1
+  Const mutate $6 = Binary mutate x$4 === mutate $5
+  If (mutate $6) then:bb2 else:bb1
 bb2:
   predecessor blocks: bb0
-  Reassign mutate x$1004 = 2
+  Reassign mutate x$8 = 2
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb2
-  Const mutate x$1003: phi(bb0: mutate x$1000, bb2: mutate x$1004)
-  Throw mutate x$1003
+  Const mutate x$7: phi(bb0: mutate x$4, bb2: mutate x$8)
+  Throw mutate x$7
 ```
 
 ## Code
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
-  if (x$1000 === 1) {
-    x$1004 = 2;
+  let x$4 = 1;
+  if (x$4 === 1) {
+    x$8 = 2;
     ("<<TODO: handle complex control flow in codegen>>");
   }
-  throw x$1003;
+  throw x$7;
 }
 
 ```
diff --git a/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md b/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md
index fe737e26b6..2d1f130bc6 100644
--- a/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/hir/ssa-while.expect.md
@@ -17,29 +17,29 @@ function foo() {
 
 ```
 bb0:
-  Let mutate x$1000 = 1
+  Let mutate x$5 = 1
   Goto bb1
 bb1:
   predecessor blocks: bb0 bb3
-  Const mutate x$1002: phi(bb0: mutate x$1000, bb3: mutate x$1005)
-  Const mutate $1001 = 10
-  Const mutate $1003 = Binary mutate x$1002 < mutate $1001
-  If (mutate $1003) then:bb3 else:bb2
+  Const mutate x$7: phi(bb0: mutate x$5, bb3: mutate x$10)
+  Const mutate $6 = 10
+  Const mutate $8 = Binary mutate x$7 < mutate $6
+  If (mutate $8) then:bb3 else:bb2
 bb3:
   predecessor blocks: bb1
-  Const mutate $1004 = 1
-  Reassign mutate x$1005 = Binary mutate x$1002 + mutate $1004
+  Const mutate $9 = 1
+  Reassign mutate x$10 = Binary mutate x$7 + mutate $9
   Goto bb1
 bb2:
   predecessor blocks: bb1
-  Return mutate x$1002
+  Return mutate x$7
 ```
 
 ## Code
 
 ```javascript
 function foo$0() {
-  let x$1000 = 1;
+  let x$5 = 1;
   ("<<TODO: handle complex control flow in codegen>>");
 }
 
diff --git a/compiler/forget/src/__tests__/hir-test.ts b/compiler/forget/src/__tests__/hir-test.ts
index 7d7229bca7..4e4b07233a 100644
--- a/compiler/forget/src/__tests__/hir-test.ts
+++ b/compiler/forget/src/__tests__/hir-test.ts
@@ -17,6 +17,7 @@ import prettier from "prettier";
 import { lower } from "../HIR/BuildHIR";
 import codegen from "../HIR/Codegen";
 import { HIRFunction } from "../HIR/HIR";
+import { Environment } from "../HIR/HIRBuilder";
 import inferReferenceEffects from "../HIR/InferReferenceEffects";
 import printHIR from "../HIR/PrintHIR";
 import buildSSA from "../HIR/SSAify";
@@ -44,10 +45,11 @@ describe("React Forget (HIR version)", () => {
       traverse(ast, {
         FunctionDeclaration: {
           enter(nodePath) {
-            const ir: HIRFunction = lower(nodePath);
+            const env: Environment = new Environment();
+            const ir: HIRFunction = lower(nodePath, env);
             inferReferenceEffects(ir);
             if (file.startsWith("ssa")) {
-              buildSSA(ir);
+              buildSSA(ir, env);
             }
             // const lifetimeGraph = buildDefUseGraph(ir);
             const textHIR = printHIR(ir.body);