diff --git a/nac3core/irrt/irrt/error_context.hpp b/nac3core/irrt/irrt/error_context.hpp
new file mode 100644
index 00000000..34de06d2
--- /dev/null
+++ b/nac3core/irrt/irrt/error_context.hpp
@@ -0,0 +1,84 @@
+#pragma once
+
+#include <irrt/int_defs.hpp>
+#include <irrt/utils.hpp>
+
+namespace {
+// nac3core's "str" struct type definition
+template <typename SizeT>
+struct Str {
+    const char* content;
+    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(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
+        this->message_template = "";
+    }
+
+    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;
+        this->param3 = param3;
+    }
+
+    bool has_error() {
+        return !cstr_utils::is_empty(message_template);
+    }
+
+    template <typename SizeT>
+    void get_error_str(Str<SizeT> *dst_str) {
+        dst_str->content = message_template;
+        dst_str->length = (SizeT) cstr_utils::length(message_template);
+    }
+};
+}
+
+extern "C" {
+void __nac3_error_context_initialize(ErrorContext* errctx, ErrorIds* error_ids) {
+    errctx->initialize(error_ids);
+}
+
+bool __nac3_error_context_has_no_error(ErrorContext* errctx) {
+    return !errctx->has_error();
+}
+
+void __nac3_error_context_get_error_str(ErrorContext* errctx, Str<int32_t> *dst_str) {
+    errctx->get_error_str<int32_t>(dst_str);
+}
+
+void __nac3_error_context_get_error_str64(ErrorContext* errctx, Str<int64_t> *dst_str) {
+    errctx->get_error_str<int64_t>(dst_str);
+}
+
+void __nac3_error_dummy_raise(ErrorContext* errctx) {
+    errctx->set_error(errctx->error_ids->runtime_error, "THROWN FROM __nac3_error_dummy_raise!!!!!!");
+}
+}
\ No newline at end of file
diff --git a/nac3core/irrt/irrt/utils.hpp b/nac3core/irrt/irrt/utils.hpp
index 6735f36b..fdf14fba 100644
--- a/nac3core/irrt/irrt/utils.hpp
+++ b/nac3core/irrt/irrt/utils.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <irrt/int_defs.hpp>
+
 namespace {
 template <typename T>
 const T& max(const T& a, const T& b) {
@@ -18,4 +20,59 @@ bool arrays_match(int len, T* as, T* bs) {
     }
     return true;
 }
+
+namespace cstr_utils {
+    bool is_empty(const char* str) {
+        return str[0] == '\0';
+    }
+
+    int8_t compare(const char* a, const char* b) {
+        uint32_t i = 0;
+        while (true) {
+            if (a[i] < b[i]) {
+                return -1;
+            } else if (a[i] > b[i]) {
+                return 1;
+            } else { // a[i] == b[i]
+                if (a[i] == '\0') {
+                    return 0;
+                } else {
+                    i++;
+                }
+            }
+        }
+    }
+
+    int8_t equal(const char* a, const char* b) {
+        return compare(a, b) == 0;
+    }
+
+    uint32_t length(const char* str) {
+        uint32_t length = 0;
+        while (*str != '\0') {
+            length++;
+            str++;
+        }
+        return length;
+    }
+
+    bool copy(const char* src, char* dst, uint32_t dst_max_size) {
+        for (uint32_t i = 0; i < dst_max_size; i++) {
+            bool is_last = i + 1 == dst_max_size;
+            if (is_last && src[i] != '\0') {
+                dst[i] = '\0';
+                return false;
+            }
+
+            if (src[i] == '\0') {
+                dst[i] = '\0';
+                return true;
+            }
+
+            dst[i] = src[i];
+        }
+
+        __builtin_unreachable();
+    }
+}
 }
\ No newline at end of file
diff --git a/nac3core/irrt/irrt_everything.hpp b/nac3core/irrt/irrt_everything.hpp
index a1c45e1e..d0480a5b 100644
--- a/nac3core/irrt/irrt_everything.hpp
+++ b/nac3core/irrt/irrt_everything.hpp
@@ -2,4 +2,5 @@
 
 #include <irrt/core.hpp>
 #include <irrt/int_defs.hpp>
-#include <irrt/utils.hpp>
\ No newline at end of file
+#include <irrt/utils.hpp>
+#include <irrt/error_context.hpp>
\ No newline at end of file
diff --git a/nac3core/src/codegen/expr.rs b/nac3core/src/codegen/expr.rs
index c42c8444..c720470a 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_by_id(generator, error_id, msg, params, loc);
+    }
+
+    pub fn raise_exn_by_id<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")
@@ -652,6 +666,32 @@ impl<'ctx, 'a> CodeGenContext<'ctx, 'a> {
         self.raise_exn(generator, err_name, err_msg, params, loc);
         self.builder.position_at_end(then_block);
     }
+
+    pub fn make_assert_impl_by_id<G: CodeGenerator + ?Sized>(
+        &mut self,
+        generator: &mut G,
+        cond: IntValue<'ctx>,
+        err_id: IntValue<'ctx>,
+        err_msg: BasicValueEnum<'ctx>,
+        params: [Option<IntValue<'ctx>>; 3],
+        loc: Location,
+    ) {
+        let i1 = self.ctx.bool_type();
+        let i1_true = i1.const_all_ones();
+        // we assume that the condition is most probably true, so the normal path is the most
+        // probable path
+        // even if this assumption is violated, it does not matter as exception unwinding is
+        // slow anyway...
+        let cond = call_expect(self, cond, i1_true, Some("expect"));
+        let current_bb = self.builder.get_insert_block().unwrap();
+        let current_fun = current_bb.get_parent().unwrap();
+        let then_block = self.ctx.insert_basic_block_after(current_bb, "succ");
+        let exn_block = self.ctx.append_basic_block(current_fun, "fail");
+        self.builder.build_conditional_branch(cond, then_block, exn_block).unwrap();
+        self.builder.position_at_end(exn_block);
+        self.raise_exn_by_id(generator, err_id, err_msg, params, loc);
+        self.builder.position_at_end(then_block);
+    }
 }
 
 /// See [`CodeGenerator::gen_constructor`].
diff --git a/nac3core/src/codegen/irrt/error_context.rs b/nac3core/src/codegen/irrt/error_context.rs
index aca77c3e..5a6fdc83 100644
--- a/nac3core/src/codegen/irrt/error_context.rs
+++ b/nac3core/src/codegen/irrt/error_context.rs
@@ -1,13 +1,15 @@
-use crate::codegen::model::*;
+use crate::codegen::{model::*, CodeGenContext, CodeGenerator};
+
+use super::util::{get_sized_dependent_function_name, FunctionBuilder};
 
 pub struct StrFields<'ctx> {
-    content: Field<PointerModel<FixedIntModel<Byte>>>,
-    length: Field<IntModel<'ctx>>,
+    pub content: Field<PointerModel<FixedIntModel<Byte>>>,
+    pub length: Field<IntModel<'ctx>>,
 }
 
 #[derive(Debug, Clone)]
 pub struct Str<'ctx> {
-    sizet: IntModel<'ctx>,
+    pub sizet: IntModel<'ctx>,
 }
 
 impl<'ctx> IsStruct<'ctx> for Str<'ctx> {
@@ -27,10 +29,10 @@ impl<'ctx> IsStruct<'ctx> for Str<'ctx> {
 
 type ErrorId = Int32;
 pub struct ErrorIdsFields {
-    index_error: Field<FixedIntModel<ErrorId>>,
-    value_error: Field<FixedIntModel<ErrorId>>,
-    assertion_error: Field<FixedIntModel<ErrorId>>,
-    runtime_error: Field<FixedIntModel<ErrorId>>,
+    pub index_error: Field<FixedIntModel<ErrorId>>,
+    pub value_error: Field<FixedIntModel<ErrorId>>,
+    pub assertion_error: Field<FixedIntModel<ErrorId>>,
+    pub runtime_error: Field<FixedIntModel<ErrorId>>,
 }
 #[derive(Debug, Clone)]
 pub struct ErrorIds;
@@ -53,11 +55,11 @@ impl<'ctx> IsStruct<'ctx> for ErrorIds {
 }
 
 pub struct ErrorContextFields {
-    error_id: Field<FixedIntModel<ErrorId>>,
-    message_template: Field<PointerModel<FixedIntModel<Byte>>>,
-    param1: Field<FixedIntModel<Int64>>,
-    param2: Field<FixedIntModel<Int64>>,
-    param3: Field<FixedIntModel<Int64>>,
+    pub error_id: Field<FixedIntModel<ErrorId>>,
+    pub message_template: Field<PointerModel<FixedIntModel<Byte>>>,
+    pub param1: Field<FixedIntModel<Int64>>,
+    pub param2: Field<FixedIntModel<Int64>>,
+    pub param3: Field<FixedIntModel<Int64>>,
 }
 #[derive(Debug, Clone)]
 pub struct ErrorContext;
@@ -79,3 +81,102 @@ impl<'ctx> IsStruct<'ctx> for ErrorContext {
         }
     }
 }
+
+// Prepare ErrorIds
+fn build_error_ids<'ctx>(ctx: &CodeGenContext<'ctx, '_>) -> Pointer<'ctx, StructModel<ErrorIds>> {
+    // ErrorIdsLens.get_fields(ctx.ctx).assertion_error.
+    let error_ids = StructModel(ErrorIds).alloca(ctx, "error_ids");
+    let i32_model = FixedIntModel(Int32);
+    // i32_model.make_constant()
+
+    let get_string_id =
+        |string_id| i32_model.constant(ctx.ctx, ctx.resolver.get_string_id(string_id) as u64);
+
+    error_ids.gep(ctx, |f| f.index_error).store(ctx, &get_string_id("0:IndexError"));
+    error_ids.gep(ctx, |f| f.value_error).store(ctx, &get_string_id("0:ValueError"));
+    error_ids.gep(ctx, |f| f.assertion_error).store(ctx, &get_string_id("0:AssertionError"));
+    error_ids.gep(ctx, |f| f.runtime_error).store(ctx, &get_string_id("0:RuntimeError"));
+
+    error_ids
+}
+
+pub fn call_nac3_error_context_initialize<'ctx>(
+    ctx: &CodeGenContext<'ctx, '_>,
+    perrctx: &Pointer<'ctx, StructModel<ErrorContext>>,
+    perror_ids: &Pointer<'ctx, StructModel<ErrorIds>>,
+) {
+    FunctionBuilder::begin(ctx, "__nac3_error_context_initialize")
+        .arg("errctx", &PointerModel(StructModel(ErrorContext)), perrctx)
+        .arg("error_ids", &PointerModel(StructModel(ErrorIds)), perror_ids)
+        .returning_void();
+}
+
+pub fn call_nac3_error_context_has_no_error<'ctx>(
+    ctx: &CodeGenContext<'ctx, '_>,
+    errctx: &Pointer<'ctx, StructModel<ErrorContext>>,
+) -> FixedInt<'ctx, Bool> {
+    FunctionBuilder::begin(ctx, "__nac3_error_context_has_no_error")
+        .arg("errctx", &PointerModel(StructModel(ErrorContext)), errctx)
+        .returning("has_error", &FixedIntModel(Bool))
+}
+
+pub fn call_nac3_error_context_get_error_str<'ctx>(
+    sizet: IntModel<'ctx>,
+    ctx: &CodeGenContext<'ctx, '_>,
+    errctx: &Pointer<'ctx, StructModel<ErrorContext>>,
+    dst_str: &Pointer<'ctx, StructModel<Str<'ctx>>>,
+) {
+    FunctionBuilder::begin(
+        ctx,
+        &get_sized_dependent_function_name(sizet, "__nac3_error_context_get_error_str"),
+    )
+    .arg("errctx", &PointerModel(StructModel(ErrorContext)), errctx)
+    .arg("dst_str", &PointerModel(StructModel(Str { sizet })), dst_str)
+    .returning_void();
+}
+
+pub fn prepare_error_context<'ctx>(
+    ctx: &CodeGenContext<'ctx, '_>,
+) -> Pointer<'ctx, StructModel<ErrorContext>> {
+    let error_ids = build_error_ids(ctx);
+    let errctx_ptr = StructModel(ErrorContext).alloca(ctx, "errctx");
+    call_nac3_error_context_initialize(ctx, &errctx_ptr, &error_ids);
+    errctx_ptr
+}
+
+pub fn check_error_context<'ctx, G: CodeGenerator + ?Sized>(
+    generator: &mut G,
+    ctx: &mut CodeGenContext<'ctx, '_>,
+    errctx_ptr: &Pointer<'ctx, StructModel<ErrorContext>>,
+) {
+    let sizet = IntModel(generator.get_size_type(ctx.ctx));
+
+    let has_error = call_nac3_error_context_has_no_error(ctx, errctx_ptr);
+    let pstr = StructModel(Str { sizet }).alloca(ctx, "error_str");
+    call_nac3_error_context_get_error_str(sizet, ctx, errctx_ptr, &pstr);
+
+    let error_id = errctx_ptr.gep(ctx, |f| f.error_id).load(ctx, "error_id");
+    let error_str = pstr.load(ctx, "error_str");
+    let param1 = errctx_ptr.gep(ctx, |f| f.param1).load(ctx, "param1");
+    let param2 = errctx_ptr.gep(ctx, |f| f.param2).load(ctx, "param2");
+    let param3 = errctx_ptr.gep(ctx, |f| f.param3).load(ctx, "param3");
+    ctx.make_assert_impl_by_id(
+        generator,
+        has_error.value,
+        error_id.value,
+        error_str.get_llvm_value(),
+        [Some(param1.value), Some(param2.value), Some(param3.value)],
+        ctx.current_loc,
+    );
+}
+
+pub fn call_nac3_dummy_raise<G: CodeGenerator + ?Sized>(
+    generator: &mut G,
+    ctx: &mut CodeGenContext,
+) {
+    let errctx = prepare_error_context(ctx);
+    FunctionBuilder::begin(ctx, "__nac3_error_dummy_raise")
+        .arg("errctx", &PointerModel(StructModel(ErrorContext)), &errctx)
+        .returning_void();
+    check_error_context(generator, ctx, &errctx);
+}
diff --git a/nac3core/src/codegen/irrt/mod.rs b/nac3core/src/codegen/irrt/mod.rs
index dfb91611..280c7ff1 100644
--- a/nac3core/src/codegen/irrt/mod.rs
+++ b/nac3core/src/codegen/irrt/mod.rs
@@ -1,6 +1,8 @@
 use crate::typecheck::typedef::Type;
 
+pub mod error_context;
 mod test;
+mod util;
 
 use super::{
     classes::{
diff --git a/nac3core/src/codegen/irrt/util.rs b/nac3core/src/codegen/irrt/util.rs
index 4ca8882c..0716cece 100644
--- a/nac3core/src/codegen/irrt/util.rs
+++ b/nac3core/src/codegen/irrt/util.rs
@@ -17,9 +17,9 @@ fn get_size_variant(ty: IntType) -> SizeVariant {
 }
 
 #[must_use]
-pub fn get_sized_dependent_function_name(ty: IntType, fn_name: &str) -> String {
+pub fn get_sized_dependent_function_name(ty: IntModel, fn_name: &str) -> String {
     let mut fn_name = fn_name.to_owned();
-    match get_size_variant(ty) {
+    match get_size_variant(ty.0) {
         SizeVariant::Bits32 => {
             // Do nothing, `fn_name` already has the correct name
         }
@@ -51,7 +51,7 @@ impl<'ctx, 'a> FunctionBuilder<'ctx, 'a> {
         self
     }
 
-    pub fn returning<M: Model<'ctx>>(self, name: &'static str, return_model: &M) -> S::MemoryValue {
+    pub fn returning<M: Model<'ctx>>(self, name: &'static str, return_model: &M) -> M::Value {
         let (param_tys, param_vals): (Vec<_>, Vec<_>) = self.arguments.into_iter().unzip();
 
         let function = self.ctx.module.get_function(self.fn_name).unwrap_or_else(|| {
diff --git a/nac3core/src/codegen/mod.rs b/nac3core/src/codegen/mod.rs
index 85b963bb..36741905 100644
--- a/nac3core/src/codegen/mod.rs
+++ b/nac3core/src/codegen/mod.rs
@@ -23,7 +23,9 @@ use inkwell::{
     values::{BasicValueEnum, FunctionValue, IntValue, PhiValue, PointerValue},
     AddressSpace, IntPredicate, OptimizationLevel,
 };
+use irrt::error_context::Str;
 use itertools::Itertools;
+use model::{IntModel, Model, StructModel};
 use nac3parser::ast::{Location, Stmt, StrRef};
 use parking_lot::{Condvar, Mutex};
 use std::collections::{HashMap, HashSet};
@@ -647,7 +649,7 @@ pub fn gen_func_impl<
         ..primitives
     };
 
-    let mut type_cache: HashMap<_, _> = [
+    let mut type_cache: HashMap<_, BasicTypeEnum<'_>> = [
         (primitives.int32, context.i32_type().into()),
         (primitives.int64, context.i64_type().into()),
         (primitives.uint32, context.i32_type().into()),
@@ -655,19 +657,8 @@ pub fn gen_func_impl<
         (primitives.float, context.f64_type().into()),
         (primitives.bool, context.i8_type().into()),
         (primitives.str, {
-            let name = "str";
-            match module.get_struct_type(name) {
-                None => {
-                    let str_type = context.opaque_struct_type("str");
-                    let fields = [
-                        context.i8_type().ptr_type(AddressSpace::default()).into(),
-                        generator.get_size_type(context).into(),
-                    ];
-                    str_type.set_body(&fields, false);
-                    str_type.into()
-                }
-                Some(t) => t.as_basic_type_enum(),
-            }
+            let sizet = IntModel(generator.get_size_type(context));
+            StructModel(Str { sizet }).get_llvm_type(context)
         }),
         (primitives.range, RangeType::new(context).as_base_type().into()),
         (primitives.exception, {
@@ -675,10 +666,12 @@ pub fn gen_func_impl<
             if let Some(t) = module.get_struct_type(name) {
                 t.ptr_type(AddressSpace::default()).as_basic_type_enum()
             } else {
+                let sizet = IntModel(generator.get_size_type(context));
+                let str_ty = StructModel(Str { sizet }).get_llvm_type(context);
+
                 let exception = context.opaque_struct_type("Exception");
                 let int32 = context.i32_type().into();
                 let int64 = context.i64_type().into();
-                let str_ty = module.get_struct_type("str").unwrap().as_basic_type_enum();
                 let fields = [int32, str_ty, int32, int32, str_ty, str_ty, int64, int64, int64];
                 exception.set_body(&fields, false);
                 exception.ptr_type(AddressSpace::default()).as_basic_type_enum()
diff --git a/nac3core/src/codegen/numpy.rs b/nac3core/src/codegen/numpy.rs
index 7421c894..69a97853 100644
--- a/nac3core/src/codegen/numpy.rs
+++ b/nac3core/src/codegen/numpy.rs
@@ -9,7 +9,7 @@ use crate::{
         irrt::{
             calculate_len_for_slice_range, call_ndarray_calc_broadcast,
             call_ndarray_calc_broadcast_index, call_ndarray_calc_nd_indices,
-            call_ndarray_calc_size,
+            call_ndarray_calc_size, error_context::call_nac3_dummy_raise,
         },
         llvm_intrinsics::{self, call_memcpy_generic},
         stmt::{gen_for_callback_incrementing, gen_for_range_callback, gen_if_else_expr_callback},
@@ -538,6 +538,8 @@ fn call_ndarray_zeros_impl<'ctx, G: CodeGenerator + ?Sized>(
     elem_ty: Type,
     shape: BasicValueEnum<'ctx>,
 ) -> Result<NDArrayValue<'ctx>, String> {
+    call_nac3_dummy_raise(generator, ctx);
+
     let supported_types = [
         ctx.primitives.int32,
         ctx.primitives.int64,