diff --git a/packages/tests/src/benchmark/Benchmark.bs.mjs b/packages/tests/src/benchmark/Benchmark.bs.mjs
index d391e5b3..c31d4441 100644
--- a/packages/tests/src/benchmark/Benchmark.bs.mjs
+++ b/packages/tests/src/benchmark/Benchmark.bs.mjs
@@ -1,6 +1,7 @@
 // Generated by ReScript, PLEASE EDIT WITH CARE
 
 import * as Benchmark from "benchmark";
+import * as Core__Array from "@rescript/core/src/Core__Array.bs.mjs";
 import * as S$RescriptSchema from "rescript-schema/src/S.bs.mjs";
 
 function addWithPrepare(suite, name, fn) {
@@ -74,47 +75,121 @@ S$RescriptSchema.setGlobalConfig({
       disableNanNumberCheck: true
     });
 
+var schema = S$RescriptSchema.recursive(function (schema) {
+      return S$RescriptSchema.union([
+                  S$RescriptSchema.object(function (s) {
+                        s.tag("type", "A");
+                        return {
+                                TAG: "A",
+                                _0: s.f("nested", S$RescriptSchema.array(schema))
+                              };
+                      }),
+                  S$RescriptSchema.literal("B"),
+                  S$RescriptSchema.literal("C"),
+                  S$RescriptSchema.literal("D"),
+                  S$RescriptSchema.literal("E"),
+                  S$RescriptSchema.literal("F"),
+                  S$RescriptSchema.literal("G"),
+                  S$RescriptSchema.literal("H"),
+                  S$RescriptSchema.literal("I"),
+                  S$RescriptSchema.literal("J"),
+                  S$RescriptSchema.literal("K"),
+                  S$RescriptSchema.literal("L"),
+                  S$RescriptSchema.literal("M"),
+                  S$RescriptSchema.literal("N"),
+                  S$RescriptSchema.literal("O"),
+                  S$RescriptSchema.literal("P"),
+                  S$RescriptSchema.literal("Q"),
+                  S$RescriptSchema.literal("R"),
+                  S$RescriptSchema.literal("S"),
+                  S$RescriptSchema.literal("T"),
+                  S$RescriptSchema.literal("U"),
+                  S$RescriptSchema.literal("V"),
+                  S$RescriptSchema.literal("W"),
+                  S$RescriptSchema.literal("X"),
+                  S$RescriptSchema.literal("Y"),
+                  S$RescriptSchema.object(function (s) {
+                        s.tag("type", "Z");
+                        return {
+                                TAG: "Z",
+                                _0: s.f("nested", S$RescriptSchema.array(schema))
+                              };
+                      })
+                ]);
+    });
+
+var testData1 = {
+  TAG: "Z",
+  _0: Core__Array.make(2, {
+        TAG: "Z",
+        _0: Core__Array.make(2, {
+              TAG: "Z",
+              _0: Core__Array.make(2, "Y")
+            })
+      })
+};
+
+Core__Array.make(2, {
+      TAG: "A",
+      _0: Core__Array.make(2, {
+            TAG: "A",
+            _0: Core__Array.make(2, "B")
+          })
+    });
+
+function test() {
+  console.time("testData1 serialize");
+  var json = S$RescriptSchema.serializeOrRaiseWith(testData1, schema);
+  console.timeEnd("testData1 serialize");
+  console.time("testData1 parse");
+  S$RescriptSchema.parseOrRaiseWith(json, schema);
+  console.timeEnd("testData1 parse");
+  console.log(schema.parseOrThrow.toString());
+}
+
+test();
+
 var data = makeTestObject();
 
 console.time("makeAdvancedObjectSchema");
 
-var schema = makeAdvancedObjectSchema();
+var schema$1 = makeAdvancedObjectSchema();
 
 console.timeEnd("makeAdvancedObjectSchema");
 
 console.time("parseAnyWith: 1");
 
-S$RescriptSchema.parseAnyWith(data, schema);
+S$RescriptSchema.parseAnyWith(data, schema$1);
 
 console.timeEnd("parseAnyWith: 1");
 
 console.time("parseAnyWith: 2");
 
-S$RescriptSchema.parseAnyWith(data, schema);
+S$RescriptSchema.parseAnyWith(data, schema$1);
 
 console.timeEnd("parseAnyWith: 2");
 
 console.time("parseAnyWith: 3");
 
-S$RescriptSchema.parseAnyWith(data, schema);
+S$RescriptSchema.parseAnyWith(data, schema$1);
 
 console.timeEnd("parseAnyWith: 3");
 
 console.time("serializeWith: 1");
 
-S$RescriptSchema.serializeWith(data, schema);
+S$RescriptSchema.serializeWith(data, schema$1);
 
 console.timeEnd("serializeWith: 1");
 
 console.time("serializeWith: 2");
 
-S$RescriptSchema.serializeWith(data, schema);
+S$RescriptSchema.serializeWith(data, schema$1);
 
 console.timeEnd("serializeWith: 2");
 
 console.time("serializeWith: 3");
 
-S$RescriptSchema.serializeWith(data, schema);
+S$RescriptSchema.serializeWith(data, schema$1);
 
 console.timeEnd("serializeWith: 3");
 
diff --git a/packages/tests/src/benchmark/Benchmark.res b/packages/tests/src/benchmark/Benchmark.res
index 4a8fe6f2..f9530e6b 100644
--- a/packages/tests/src/benchmark/Benchmark.res
+++ b/packages/tests/src/benchmark/Benchmark.res
@@ -103,6 +103,104 @@ S.setGlobalConfig({
   disableNanNumberCheck: true,
 })
 
+// Reported in https://gist.github.com/cknitt/4ac6813a3f3bc907187105e01a4324ca
+module CrazyUnion = {
+  type rec test =
+    | A(array<test>)
+    | B
+    | C
+    | D
+    | E
+    | F
+    | G
+    | H
+    | I
+    | J
+    | K
+    | L
+    | M
+    | N
+    | O
+    | P
+    | Q
+    | R
+    | S
+    | T
+    | U
+    | V
+    | W
+    | X
+    | Y
+    | Z(array<test>)
+
+  let schema = S.recursive(schema =>
+    S.union([
+      S.object(s => {
+        s.tag("type", "A")
+        A(s.field("nested", S.array(schema)))
+      }),
+      S.literal(B),
+      S.literal(C),
+      S.literal(D),
+      S.literal(E),
+      S.literal(F),
+      S.literal(G),
+      S.literal(H),
+      S.literal(I),
+      S.literal(J),
+      S.literal(K),
+      S.literal(L),
+      S.literal(M),
+      S.literal(N),
+      S.literal(O),
+      S.literal(P),
+      S.literal(Q),
+      S.literal(R),
+      S.literal(S),
+      S.literal(T),
+      S.literal(U),
+      S.literal(V),
+      S.literal(W),
+      S.literal(X),
+      S.literal(Y),
+      S.object(s => {
+        s.tag("type", "Z")
+        Z(s.field("nested", S.array(schema)))
+      }),
+    ])
+  )
+
+  let testData1 = Z(Array.make(~length=2, Z(Array.make(~length=2, Z(Array.make(~length=2, Y))))))
+
+  let _testData2 = A(Array.make(~length=2, A(Array.make(~length=2, A(Array.make(~length=2, B))))))
+
+  let test = () => {
+    Console.time("testData1 serialize")
+    let json = S.serializeOrRaiseWith(testData1, schema)
+    Console.timeEnd("testData1 serialize")
+
+    Console.time("testData1 parse")
+    let _ = S.parseOrRaiseWith(json, schema)
+    Console.timeEnd("testData1 parse")
+
+    // Console.time("testData2 serialize")
+    // let json = S.serializeOrRaiseWith(testData2, schema)
+    // Console.timeEnd("testData2 serialize")
+
+    // Console.time("testData2 parse")
+    // let _ = S.parseOrRaiseWith(json, schema)
+    // Console.timeEnd("testData2 parse")
+
+    Js.log((schema->Obj.magic)["parseOrThrow"]["toString"]())
+  }
+}
+
+// testData1 serialize: 5.414s
+// testData1 parse: 5.519s
+// testData2 serialize: 70.864ms
+// testData2 parse: 70.967ms
+CrazyUnion.test()
+
 let data = makeTestObject()
 Console.time("makeAdvancedObjectSchema")
 let schema = makeAdvancedObjectSchema()
diff --git a/packages/tests/src/core/S_parseAnyAsyncInStepsWith_deprecatedTest.bs.mjs b/packages/tests/src/core/S_parseAnyAsyncInStepsWith_deprecatedTest.bs.mjs
new file mode 100644
index 00000000..d856702b
--- /dev/null
+++ b/packages/tests/src/core/S_parseAnyAsyncInStepsWith_deprecatedTest.bs.mjs
@@ -0,0 +1,2 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+/* This output is empty. Its source's type definitions, externals and/or unused code got optimized away. */
diff --git a/packages/tests/src/core/S_union_test.res b/packages/tests/src/core/S_union_test.res
index 3150d808..c1a3d86c 100644
--- a/packages/tests/src/core/S_union_test.res
+++ b/packages/tests/src/core/S_union_test.res
@@ -500,3 +500,86 @@ module CknittelBugReport = {
     )
   })
 }
+
+// Reported in https://gist.github.com/cknitt/4ac6813a3f3bc907187105e01a4324ca
+module CrazyUnion = {
+  type rec test =
+    | A(array<test>)
+    | B
+    | C
+    | D
+    | E
+    | F
+    | G
+    | H
+    | I
+    | J
+    | K
+    | L
+    | M
+    | N
+    | O
+    | P
+    | Q
+    | R
+    | S
+    | T
+    | U
+    | V
+    | W
+    | X
+    | Y
+    | Z(array<test>)
+
+  let schema = S.recursive(schema =>
+    S.union([
+      S.object(s => {
+        s.tag("type", "A")
+        A(s.field("nested", S.array(schema)))
+      }),
+      S.literal(B),
+      S.literal(C),
+      S.literal(D),
+      S.literal(E),
+      S.literal(F),
+      S.literal(G),
+      S.literal(H),
+      S.literal(I),
+      S.literal(J),
+      S.literal(K),
+      S.literal(L),
+      S.literal(M),
+      S.literal(N),
+      S.literal(O),
+      S.literal(P),
+      S.literal(Q),
+      S.literal(R),
+      S.literal(S),
+      S.literal(T),
+      S.literal(U),
+      S.literal(V),
+      S.literal(W),
+      S.literal(X),
+      S.literal(Y),
+      S.object(s => {
+        s.tag("type", "Z")
+        Z(s.field("nested", S.array(schema)))
+      }),
+    ])
+  )
+
+  test("Compiled code snapshot of crazy union", t => {
+    S.setGlobalConfig({})
+    t->U.assertCompiledCode(
+      ~schema,
+      ~op=#Parse,
+      `i=>{let r0=i=>{let v6;try{if(!i||i.constructor!==Object){e[0](i)}let v0=i["type"],v1=i["nested"],v5=[];v0==="A"||e[1](v0);if(!Array.isArray(v1)){e[2](v1)}for(let v2=0;v2<v1.length;++v2){let v4;try{v4=r0(v1[v2])}catch(v3){if(v3&&v3.s===s){v3.path="[\\"nested\\"]"+\'["\'+v2+\'"]\'+v3.path}throw v3}v5.push(v4)}v6={"TAG":e[3],"_0":v5,}}catch(e0){try{i==="B"||e[4](i);v6=i}catch(e1){try{i==="C"||e[5](i);v6=i}catch(e2){try{i==="D"||e[6](i);v6=i}catch(e3){try{i==="E"||e[7](i);v6=i}catch(e4){try{i==="F"||e[8](i);v6=i}catch(e5){try{i==="G"||e[9](i);v6=i}catch(e6){try{i==="H"||e[10](i);v6=i}catch(e7){try{i==="I"||e[11](i);v6=i}catch(e8){try{i==="J"||e[12](i);v6=i}catch(e9){try{i==="K"||e[13](i);v6=i}catch(e10){try{i==="L"||e[14](i);v6=i}catch(e11){try{i==="M"||e[15](i);v6=i}catch(e12){try{i==="N"||e[16](i);v6=i}catch(e13){try{i==="O"||e[17](i);v6=i}catch(e14){try{i==="P"||e[18](i);v6=i}catch(e15){try{i==="Q"||e[19](i);v6=i}catch(e16){try{i==="R"||e[20](i);v6=i}catch(e17){try{i==="S"||e[21](i);v6=i}catch(e18){try{i==="T"||e[22](i);v6=i}catch(e19){try{i==="U"||e[23](i);v6=i}catch(e20){try{i==="V"||e[24](i);v6=i}catch(e21){try{i==="W"||e[25](i);v6=i}catch(e22){try{i==="X"||e[26](i);v6=i}catch(e23){try{i==="Y"||e[27](i);v6=i}catch(e24){try{if(!i||i.constructor!==Object){e[28](i)}let v7=i["type"],v8=i["nested"],v12=[];v7==="Z"||e[29](v7);if(!Array.isArray(v8)){e[30](v8)}for(let v9=0;v9<v8.length;++v9){let v11;try{v11=r0(v8[v9])}catch(v10){if(v10&&v10.s===s){v10.path="[\\"nested\\"]"+\'["\'+v9+\'"]\'+v10.path}throw v10}v12.push(v11)}v6={"TAG":e[31],"_0":v12,}}catch(e25){e[32]([e0,e1,e2,e3,e4,e5,e6,e7,e8,e9,e10,e11,e12,e13,e14,e15,e16,e17,e18,e19,e20,e21,e22,e23,e24,e25,])}}}}}}}}}}}}}}}}}}}}}}}}}}return v6};return r0(i)}`,
+    )
+    S.setGlobalConfig({})
+    t->U.assertCompiledCode(
+      ~schema,
+      ~op=#Serialize,
+      `i=>{let r0=i=>{let v5,v6,v12;try{let v0=i["_0"],v4=[];if(i["TAG"]!==e[0]){e[1](i["TAG"])}for(let v1=0;v1<v0.length;++v1){let v3;try{v3=r0(v0[v1])}catch(v2){if(v2&&v2.s===s){v2.path="[\\"_0\\"]"+\'["\'+v1+\'"]\'+v2.path}throw v2}v4.push(v3)}v5={"type":e[2],"nested":v4,};if(!v5||v5.constructor!==Object){e[3](v5)}v6=v5}catch(e0){try{i==="B"||e[4](i);v6=i}catch(e1){try{i==="C"||e[5](i);v6=i}catch(e2){try{i==="D"||e[6](i);v6=i}catch(e3){try{i==="E"||e[7](i);v6=i}catch(e4){try{i==="F"||e[8](i);v6=i}catch(e5){try{i==="G"||e[9](i);v6=i}catch(e6){try{i==="H"||e[10](i);v6=i}catch(e7){try{i==="I"||e[11](i);v6=i}catch(e8){try{i==="J"||e[12](i);v6=i}catch(e9){try{i==="K"||e[13](i);v6=i}catch(e10){try{i==="L"||e[14](i);v6=i}catch(e11){try{i==="M"||e[15](i);v6=i}catch(e12){try{i==="N"||e[16](i);v6=i}catch(e13){try{i==="O"||e[17](i);v6=i}catch(e14){try{i==="P"||e[18](i);v6=i}catch(e15){try{i==="Q"||e[19](i);v6=i}catch(e16){try{i==="R"||e[20](i);v6=i}catch(e17){try{i==="S"||e[21](i);v6=i}catch(e18){try{i==="T"||e[22](i);v6=i}catch(e19){try{i==="U"||e[23](i);v6=i}catch(e20){try{i==="V"||e[24](i);v6=i}catch(e21){try{i==="W"||e[25](i);v6=i}catch(e22){try{i==="X"||e[26](i);v6=i}catch(e23){try{i==="Y"||e[27](i);v6=i}catch(e24){try{let v7=i["_0"],v11=[];if(i["TAG"]!==e[28]){e[29](i["TAG"])}for(let v8=0;v8<v7.length;++v8){let v10;try{v10=r0(v7[v8])}catch(v9){if(v9&&v9.s===s){v9.path="[\\"_0\\"]"+\'["\'+v8+\'"]\'+v9.path}throw v9}v11.push(v10)}v12={"type":e[30],"nested":v11,};if(!v12||v12.constructor!==Object){e[31](v12)}v6=v12}catch(e25){e[32]([e0,e1,e2,e3,e4,e5,e6,e7,e8,e9,e10,e11,e12,e13,e14,e15,e16,e17,e18,e19,e20,e21,e22,e23,e24,e25,])}}}}}}}}}}}}}}}}}}}}}}}}}}return v6};return r0(i)}`,
+    )
+  })
+}
diff --git a/src/S_Core.bs.mjs b/src/S_Core.bs.mjs
index 1896566f..6c039990 100644
--- a/src/S_Core.bs.mjs
+++ b/src/S_Core.bs.mjs
@@ -66,8 +66,11 @@ function toJsResult(result) {
   }
 }
 
-class RescriptSchemaError extends Error {
+// let index = 0;
+    class RescriptSchemaError extends Error {
       constructor(code, operation, path) {
+        // console.log(index)
+        // index = index + 1;
         super();
         this.operation = operation;
         this.code = code;
diff --git a/src/S_Core.res b/src/S_Core.res
index 7374693b..631a47fe 100644
--- a/src/S_Core.res
+++ b/src/S_Core.res
@@ -379,8 +379,11 @@ let toJsResult = (result: result<'value, error>): jsResult<'value> => {
 
 module InternalError = {
   %%raw(`
+    // let index = 0;
     class RescriptSchemaError extends Error {
       constructor(code, operation, path) {
+        // console.log(index)
+        // index = index + 1;
         super();
         this.operation = operation;
         this.code = code;
diff --git a/test.js b/test.js
index 952a7610..1a2f24ef 100644
--- a/test.js
+++ b/test.js
@@ -1,14 +1,226 @@
 (i) => {
-  return e[0](i).then((v0) => {
-    return e[1](v0)
-      .then((v1) => {
-        if (typeof v1 !== "string") {
-          e[2](v1);
+  let r0 = (i) => {
+    let v5, v6, v12;
+    try {
+      let v0 = i["_0"],
+        v4 = [];
+      if (i["TAG"] !== e[0]) {
+        e[1](i["TAG"]);
+      }
+      for (let v1 = 0; v1 < v0.length; ++v1) {
+        let v3;
+        try {
+          v3 = r0(v0[v1]);
+        } catch (v2) {
+          if (v2 && v2.s === s) {
+            v2.path = '["_0"]' + '["' + v1 + '"]' + v2.path;
+          }
+          throw v2;
         }
-        return v1;
-      })
-      .then((v2) => {
-        return e[3](v2);
-      });
-  });
+        v4.push(v3);
+      }
+      v5 = { type: e[2], nested: v4 };
+      if (!v5 || v5.constructor !== Object) {
+        e[3](v5);
+      }
+      v6 = v5;
+    } catch (e0) {
+      try {
+        i === "B" || e[4](i);
+        v6 = i;
+      } catch (e1) {
+        try {
+          i === "C" || e[5](i);
+          v6 = i;
+        } catch (e2) {
+          try {
+            i === "D" || e[6](i);
+            v6 = i;
+          } catch (e3) {
+            try {
+              i === "E" || e[7](i);
+              v6 = i;
+            } catch (e4) {
+              try {
+                i === "F" || e[8](i);
+                v6 = i;
+              } catch (e5) {
+                try {
+                  i === "G" || e[9](i);
+                  v6 = i;
+                } catch (e6) {
+                  try {
+                    i === "H" || e[10](i);
+                    v6 = i;
+                  } catch (e7) {
+                    try {
+                      i === "I" || e[11](i);
+                      v6 = i;
+                    } catch (e8) {
+                      try {
+                        i === "J" || e[12](i);
+                        v6 = i;
+                      } catch (e9) {
+                        try {
+                          i === "K" || e[13](i);
+                          v6 = i;
+                        } catch (e10) {
+                          try {
+                            i === "L" || e[14](i);
+                            v6 = i;
+                          } catch (e11) {
+                            try {
+                              i === "M" || e[15](i);
+                              v6 = i;
+                            } catch (e12) {
+                              try {
+                                i === "N" || e[16](i);
+                                v6 = i;
+                              } catch (e13) {
+                                try {
+                                  i === "O" || e[17](i);
+                                  v6 = i;
+                                } catch (e14) {
+                                  try {
+                                    i === "P" || e[18](i);
+                                    v6 = i;
+                                  } catch (e15) {
+                                    try {
+                                      i === "Q" || e[19](i);
+                                      v6 = i;
+                                    } catch (e16) {
+                                      try {
+                                        i === "R" || e[20](i);
+                                        v6 = i;
+                                      } catch (e17) {
+                                        try {
+                                          i === "S" || e[21](i);
+                                          v6 = i;
+                                        } catch (e18) {
+                                          try {
+                                            i === "T" || e[22](i);
+                                            v6 = i;
+                                          } catch (e19) {
+                                            try {
+                                              i === "U" || e[23](i);
+                                              v6 = i;
+                                            } catch (e20) {
+                                              try {
+                                                i === "V" || e[24](i);
+                                                v6 = i;
+                                              } catch (e21) {
+                                                try {
+                                                  i === "W" || e[25](i);
+                                                  v6 = i;
+                                                } catch (e22) {
+                                                  try {
+                                                    i === "X" || e[26](i);
+                                                    v6 = i;
+                                                  } catch (e23) {
+                                                    try {
+                                                      i === "Y" || e[27](i);
+                                                      v6 = i;
+                                                    } catch (e24) {
+                                                      try {
+                                                        let v7 = i["_0"],
+                                                          v11 = [];
+                                                        if (
+                                                          i["TAG"] !== e[28]
+                                                        ) {
+                                                          e[29](i["TAG"]);
+                                                        }
+                                                        for (
+                                                          let v8 = 0;
+                                                          v8 < v7.length;
+                                                          ++v8
+                                                        ) {
+                                                          let v10;
+                                                          try {
+                                                            v10 = r0(v7[v8]);
+                                                          } catch (v9) {
+                                                            if (
+                                                              v9 &&
+                                                              v9.s === s
+                                                            ) {
+                                                              v9.path =
+                                                                '["_0"]' +
+                                                                '["' +
+                                                                v8 +
+                                                                '"]' +
+                                                                v9.path;
+                                                            }
+                                                            throw v9;
+                                                          }
+                                                          v11.push(v10);
+                                                        }
+                                                        v12 = {
+                                                          type: e[30],
+                                                          nested: v11,
+                                                        };
+                                                        if (
+                                                          !v12 ||
+                                                          v12.constructor !==
+                                                            Object
+                                                        ) {
+                                                          e[31](v12);
+                                                        }
+                                                        v6 = v12;
+                                                      } catch (e25) {
+                                                        e[32]([
+                                                          e0,
+                                                          e1,
+                                                          e2,
+                                                          e3,
+                                                          e4,
+                                                          e5,
+                                                          e6,
+                                                          e7,
+                                                          e8,
+                                                          e9,
+                                                          e10,
+                                                          e11,
+                                                          e12,
+                                                          e13,
+                                                          e14,
+                                                          e15,
+                                                          e16,
+                                                          e17,
+                                                          e18,
+                                                          e19,
+                                                          e20,
+                                                          e21,
+                                                          e22,
+                                                          e23,
+                                                          e24,
+                                                          e25,
+                                                        ]);
+                                                      }
+                                                    }
+                                                  }
+                                                }
+                                              }
+                                            }
+                                          }
+                                        }
+                                      }
+                                    }
+                                  }
+                                }
+                              }
+                            }
+                          }
+                        }
+                      }
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+    return v6;
+  };
+  return r0(i);
 };