diff --git a/nac3core/irrt/irrt/error_context.hpp b/nac3core/irrt/irrt/error_context.hpp
index c1dfa6ec..824f6eb7 100644
--- a/nac3core/irrt/irrt/error_context.hpp
+++ b/nac3core/irrt/irrt/error_context.hpp
@@ -11,22 +11,38 @@ struct Str {
     SizeT length;
 };
 
+// A limited set of errors IRRT could use.
+typedef uint32_t ErrorId;
+struct ErrorIds {
+    ErrorId index_error;
+    ErrorId value_error;
+    ErrorId assertion_error;
+    ErrorId runtime_error;
+};
+
 struct ErrorContext {
+    // Context
+    ErrorIds* error_ids;
+
+    // Error thrown by IRRT
+    ErrorId error_id;
     const char* message_template; // MUST BE `&'static`
     uint64_t param1;
     uint64_t param2;
     uint64_t param3;
 
-    void initialize() {
+    void initialize(ErrorIds* error_ids) {
+        this->error_ids = error_ids;
         clear_error();
     }
 
     void clear_error() {
         // Point the message_template to an empty str. Don't set it to nullptr as a sentinel
-        set_error("");
+        this->message_template = "";
     }
 
-    void set_error(const char* message, uint64_t param1 = 0, uint64_t param2 = 0, uint64_t param3 = 0) {
+    void set_error(ErrorId error_id, const char* message, uint64_t param1 = 0, uint64_t param2 = 0, uint64_t param3 = 0) {
+        this->error_id = error_id;
         this->message_template = message;
         this->param1 = param1;
         this->param2 = param2;
@@ -47,8 +63,8 @@ struct ErrorContext {
 
 extern "C" {
 
-void __nac3_error_context_initialize(ErrorContext* errctx) {
-    errctx->initialize();
+void __nac3_error_context_initialize(ErrorContext* errctx, ErrorIds* error_ids) {
+    errctx->initialize(error_ids);
 }
 
 uint8_t __nac3_error_context_has_no_error(ErrorContext* errctx) {
@@ -64,6 +80,6 @@ void __nac3_error_context_get_error_str64(ErrorContext* errctx, Str<int64_t> *ds
 }
 
 void __nac3_error_dummy_raise(ErrorContext* errctx) {
-    errctx->set_error("THROWN FROM __nac3_error_dummy_raise!!!!!!");
+    errctx->set_error(errctx->error_ids->runtime_error, "THROWN FROM __nac3_error_dummy_raise!!!!!!");
 }
 }
\ No newline at end of file
diff --git a/nac3core/src/codegen/expr.rs b/nac3core/src/codegen/expr.rs
index c42c8444..c9f96385 100644
--- a/nac3core/src/codegen/expr.rs
+++ b/nac3core/src/codegen/expr.rs
@@ -576,6 +576,21 @@ impl<'ctx, 'a> CodeGenContext<'ctx, 'a> {
         params: [Option<IntValue<'ctx>>; 3],
         loc: Location,
     ) {
+        let error_id = self.resolver.get_string_id(name);
+        let error_id = self.ctx.i32_type().const_int(error_id as u64, false);
+        self.raise_exn_impl(generator, error_id, msg, params, loc);
+    }
+
+    pub fn raise_exn_impl<G: CodeGenerator + ?Sized>(
+        &mut self,
+        generator: &mut G,
+        error_id: IntValue<'ctx>,
+        msg: BasicValueEnum<'ctx>,
+        params: [Option<IntValue<'ctx>>; 3],
+        loc: Location,
+    ) {
+        assert_eq!(error_id.get_type().get_bit_width(), 32);
+
         let zelf = if let Some(exception_val) = self.exception_val {
             exception_val
         } else {
@@ -588,8 +603,7 @@ impl<'ctx, 'a> CodeGenContext<'ctx, 'a> {
         let zero = int32.const_zero();
         unsafe {
             let id_ptr = self.builder.build_in_bounds_gep(zelf, &[zero, zero], "exn.id").unwrap();
-            let id = self.resolver.get_string_id(name);
-            self.builder.build_store(id_ptr, int32.const_int(id as u64, false)).unwrap();
+            self.builder.build_store(id_ptr, error_id).unwrap();
             let ptr = self
                 .builder
                 .build_in_bounds_gep(zelf, &[zero, int32.const_int(5, false)], "exn.msg")
diff --git a/nac3core/src/codegen/irrt/classes.rs b/nac3core/src/codegen/irrt/classes.rs
index dfa8c5d2..c1b12c6e 100644
--- a/nac3core/src/codegen/irrt/classes.rs
+++ b/nac3core/src/codegen/irrt/classes.rs
@@ -93,7 +93,36 @@ impl<'ctx> StructureOptic<'ctx> for IrrtStringLens {
     }
 }
 
+pub struct ErrorIdsFields<'ctx> {
+    pub index_error: GepGetter<IntLens<'ctx>>,
+    pub value_error: GepGetter<IntLens<'ctx>>,
+    pub assertion_error: GepGetter<IntLens<'ctx>>,
+    pub runtime_error: GepGetter<IntLens<'ctx>>,
+}
+
+#[derive(Debug, Clone)]
+pub struct ErrorIdsLens;
+
+impl<'ctx> StructureOptic<'ctx> for ErrorIdsLens {
+    type Fields = ErrorIdsFields<'ctx>;
+
+    fn struct_name(&self) -> &'static str {
+        "ErrorIds"
+    }
+
+    fn build_fields(&self, builder: &mut FieldBuilder<'ctx>) -> Self::Fields {
+        let i32_lens = IntLens(builder.ctx.i32_type());
+        ErrorIdsFields {
+            index_error: builder.add_field("index_error", i32_lens),
+            value_error: builder.add_field("value_error", i32_lens),
+            assertion_error: builder.add_field("assertion_error", i32_lens),
+            runtime_error: builder.add_field("runtime_error", i32_lens),
+        }
+    }
+}
+
 pub struct ErrorContextFields<'ctx> {
+    pub error_ids: GepGetter<AddressLens<ErrorIdsLens>>,
     pub message_template: GepGetter<AddressLens<IntLens<'ctx>>>,
     pub param1: GepGetter<IntLens<'ctx>>,
     pub param2: GepGetter<IntLens<'ctx>>,
@@ -115,6 +144,7 @@ impl<'ctx> StructureOptic<'ctx> for ErrorContextLens {
         builder: &mut crate::codegen::optics::FieldBuilder<'ctx>,
     ) -> Self::Fields {
         ErrorContextFields {
+            error_ids: builder.add_field("error_ids", AddressLens(ErrorIdsLens)),
             message_template: builder
                 .add_field("message_template", AddressLens(IntLens(builder.ctx.i8_type()))),
             param1: builder.add_field("param1", IntLens(builder.ctx.i64_type())),
diff --git a/nac3core/src/codegen/irrt/new.rs b/nac3core/src/codegen/irrt/new.rs
index 5c992d4b..0dc78c62 100644
--- a/nac3core/src/codegen/irrt/new.rs
+++ b/nac3core/src/codegen/irrt/new.rs
@@ -3,15 +3,13 @@ use inkwell::{
     values::{AnyValue, BasicMetadataValueEnum, IntValue},
 };
 
-use crate::{
-    codegen::{
-        optics::{Address, AddressLens, IntLens, Optic, OpticValue, Prism},
-        CodeGenContext, CodeGenerator,
-    },
-    util::SizeVariant,
+use crate::codegen::{
+    optics::{Address, AddressLens, IntLens, Optic, OpticValue, Prism},
+    CodeGenContext, CodeGenerator,
 };
+use crate::util::SizeVariant;
 
-use super::classes::{ErrorContextLens, StrLens};
+use super::classes::{ErrorContextLens, ErrorIdsLens, StrLens};
 
 fn get_size_variant(ty: IntType) -> SizeVariant {
     match ty.get_bit_width() {
@@ -82,12 +80,34 @@ impl<'ctx, 'a> FunctionBuilder<'ctx, 'a> {
     }
 }
 
+fn build_error_ids<'ctx>(ctx: &CodeGenContext<'ctx, '_>) -> Address<'ctx, ErrorIdsLens> {
+    // ErrorIdsLens.get_fields(ctx.ctx).assertion_error.
+    let error_ids = ErrorIdsLens.alloca(ctx, "error_ids");
+    let llvm_i32 = ctx.ctx.i32_type();
+
+    let get_string_id =
+        |string_id| llvm_i32.const_int(ctx.resolver.get_string_id(string_id) as u64, false);
+
+    error_ids.view(ctx, |fields| &fields.index_error).store(ctx, &get_string_id("0:IndexError"));
+    error_ids.view(ctx, |fields| &fields.value_error).store(ctx, &get_string_id("0:ValueError"));
+    error_ids
+        .view(ctx, |fields| &fields.assertion_error)
+        .store(ctx, &get_string_id("0:AssertionError"));
+    error_ids
+        .view(ctx, |fields| &fields.runtime_error)
+        .store(ctx, &get_string_id("0:RuntimeError"));
+
+    error_ids
+}
+
 pub fn call_nac3_error_context_initialize<'ctx>(
     ctx: &CodeGenContext<'ctx, '_>,
     errctx: &Address<'ctx, ErrorContextLens>,
+    error_ids: &Address<'ctx, ErrorIdsLens>,
 ) {
     FunctionBuilder::begin(ctx, "__nac3_error_context_initialize")
         .arg("errctx", &AddressLens(ErrorContextLens), errctx)
+        .arg("error_ids", &AddressLens(ErrorIdsLens), error_ids)
         .returning_void();
 }
 
@@ -130,9 +150,10 @@ pub fn test_dummy_raise<G: CodeGenerator + ?Sized>(
 ) {
     let size_type = generator.get_size_type(ctx.ctx);
 
+    let error_ids = build_error_ids(ctx);
     let errctx_ptr = ErrorContextLens.alloca(ctx, "errctx");
 
-    call_nac3_error_context_initialize(ctx, &errctx_ptr);
+    call_nac3_error_context_initialize(ctx, &errctx_ptr, &error_ids);
     call_nac3_dummy_raise(ctx, &errctx_ptr);
 
     let has_error = call_nac3_error_context_has_no_error(ctx, &errctx_ptr);
diff --git a/nac3core/src/codegen/optics.rs b/nac3core/src/codegen/optics.rs
index 8a7b0439..e38d30aa 100644
--- a/nac3core/src/codegen/optics.rs
+++ b/nac3core/src/codegen/optics.rs
@@ -172,7 +172,7 @@ impl<'ctx, AddresseeOptic: MemoryGetter<'ctx>> Address<'ctx, AddresseeOptic> {
 
 // To make [`Address`] convenient to use
 impl<'ctx, AddresseeOptic: MemorySetter<'ctx>> Address<'ctx, AddresseeOptic> {
-    pub fn set(&self, ctx: &CodeGenContext<'ctx, '_>, value: &AddresseeOptic::Value) {
+    pub fn store(&self, ctx: &CodeGenContext<'ctx, '_>, value: &AddresseeOptic::Value) {
         self.addressee_optic.set(ctx, self.address, value);
     }
 }