core/model: introduce Model<'ctx> abstraction

nac3core/src/codegen/mod.rs

@@ -41,6 +41,7 @@ pub mod extern_fns;
 mod generator;
 pub mod irrt;
 pub mod llvm_intrinsics;
+pub mod model;
 pub mod numpy;
 pub mod stmt;
 

nac3core/src/codegen/model/core.rs

@@ -0,0 +1,173 @@
+use inkwell::{
+    context::Context,
+    types::{BasicType, BasicTypeEnum},
+    values::{BasicValue, BasicValueEnum, PointerValue},
+};
+
+use crate::codegen::{CodeGenContext, CodeGenerator};
+
+use super::{slice::ArraySlice, Int, Pointer};
+
+/*
+Explanation on the abstraction:
+
+    In LLVM, there are TYPES and VALUES.
+
+    Inkwell gives us TYPES [`BasicTypeEnum<'ctx>`] and VALUES [`BasicValueEnum<'ctx>`],
+        but by themselves, they lack a lot of Rust compile-time known info.
+
+        e.g., You did `let ptr = builder.build_alloca(my_llvm_ndarray_struct_ty)`,
+        but `ptr` is just a `PointerValue<'ctx>`, almost everything about the
+        underlying `my_llvm_ndarray_struct_ty` is gone.
+
+    The `Model` abstraction is a wrapper around inkwell TYPES and VALUES but with
+        a richer interface.
+
+    `Model<'ctx>` is a wrapper around for an inkwell TYPE:
+        - `NIntModel<Byte>` is a i8.
+        - `NIntModel<Int32>` is a i32.
+        - `NIntModel<Int64>` is a i64.
+        - `IntModel` is a carrier for an inkwell `IntType<'ctx>`,
+              used when the type is dynamic/cannot be specified in Rust compile-time.
+        - `PointerModel<'ctx, E>` is a wrapper for `PointerType<'ctx>`,
+              where `E` is another `Model<'ctx>` that describes the element type of the pointer.
+        - `StructModel<'ctx, NDArray>` is a wrapper for `StructType<'ctx>`,
+              with additional information encoded within `NDArray`. (See `IsStruct<'ctx>`)
+
+    `Model<'ctx>::Value`/`ModelValue<'ctx>` is a wrapper around for an inkwell VALUE:
+        - `NInt<'ctx, T>` is a value of `NIntModel<'ctx, T>`,
+              where `T` could be `Byte`, `Int32`, or `Int64`.
+        - `Pointer<'ctx, E>` is a value of `PointerModel<'ctx, E>`.
+
+    Other interesting utilities:
+        - Given a `Model<'ctx>`, say, `let ndarray_model = StructModel<'ctx, NDArray>`,
+              you are do `ndarray_model.alloca(ctx, "my_ndarray")` to get a `Pointer<'ctx, Struct<'ctx, NDArray>>`,
+              notice that all LLVM type information are preserved.
+        - For a `let my_ndarray = Pointer<'ctx, StructModel<NDArray>>`, you can access a field by doing
+              `my_ndarray.gep(ctx, |f| f.itemsize).load() // or .store()`, and you can chain them
+              together for nested structures.
+
+    A brief summary on the `Model<'ctx>` and `ModelValue<'ctx>` traits:
+        - Model<'ctx>
+            // The associated ModelValue of this Model
+            - type Value: ModelValue<'ctx>
+
+            // Get the LLVM type of this Model
+            - fn get_llvm_type(&self)
+
+            // Check if the input type is equal to the LLVM type of this Model
+            // NOTE: this function is provideed through `CanCheckLLVMType<'ctx>`
+            - fn check_llvm_type(&self, ty) -> Result<(), String>
+
+            // Check if the input value's type is equal to the LLVM type of this Model.
+            //
+            // If so, wrap it with `Self::Value`.
+            - fn review_value<V: BasicType<'ctx>>(&self, val: V) -> Result<Self::Value, String>
+
+        - ModelValue<'ctx>
+            // get the LLVM value of this ModelValue
+            - fn get_llvm_value(&self) -> BasicValueEnum<'ctx>
+*/
+
+/// A value that belongs to/produced by a [`Model<'ctx>`]
+pub trait ModelValue<'ctx>: Clone + Copy {
+    /// Get the LLVM value of this [`ModelValue<'ctx>`]
+    fn get_llvm_value(&self) -> BasicValueEnum<'ctx>;
+}
+
+// NOTE: Should have been within [`Model<'ctx>`],
+// but rust object safety requirements made it necessary to
+// split the trait.
+pub trait CanCheckLLVMType<'ctx> {
+    /// See [`Model::check_llvm_type`]
+    fn check_llvm_type_impl(
+        &self,
+        ctx: &'ctx Context,
+        ty: BasicTypeEnum<'ctx>,
+    ) -> Result<(), String>;
+}
+
+pub trait Model<'ctx>: Clone + Copy + CanCheckLLVMType<'ctx> + Sized {
+    /// The associated [`ModelValue<'ctx>`] of this Model.
+    type Value: ModelValue<'ctx>;
+
+    /// Get the LLVM type of this [`Model<'ctx>`]
+    fn get_llvm_type(&self, ctx: &'ctx Context) -> BasicTypeEnum<'ctx>;
+
+    /// Check if the input type is equal to the LLVM type of this Model.
+    ///
+    /// If it doesn't match, an [`Err`] with a human-readable message is
+    /// thrown explaining *how* it was different. Meant for debugging.
+    fn check_llvm_type<T: BasicType<'ctx>>(&self, ctx: &'ctx Context, ty: T) -> Result<(), String> {
+        self.check_llvm_type_impl(ctx, ty.as_basic_type_enum())
+    }
+
+    /// Check if the input value's type is equal to the LLVM type of this Model
+    /// (using [`Model::check_llvm_type`]).
+    ///
+    /// If so, wrap it with [`Model::Value`].
+    fn review_value<V: BasicValue<'ctx>>(
+        &self,
+        ctx: &'ctx Context,
+        value: V,
+    ) -> Result<Self::Value, String>;
+
+    /// Check if [`Self::Value`] has the correct type described by this [`Model<'ctx>`]
+    fn check_value(&self, ctx: &'ctx Context, value: Self::Value) -> Result<(), String> {
+        self.review_value(ctx, value.get_llvm_value())?;
+        Ok(())
+    }
+
+    /// Build an instruction to allocate a value with the LLVM type of this [`Model<'ctx>`].
+    fn alloca(&self, ctx: &CodeGenContext<'ctx, '_>, name: &str) -> Pointer<'ctx, Self> {
+        Pointer {
+            element: *self,
+            value: ctx.builder.build_alloca(self.get_llvm_type(ctx.ctx), name).unwrap(),
+        }
+    }
+
+    /// Build an instruction to allocate an array of the LLVM type of this [`Model<'ctx>`].
+    fn array_alloca(
+        &self,
+        ctx: &CodeGenContext<'ctx, '_>,
+        count: Int<'ctx>,
+        name: &str,
+    ) -> ArraySlice<'ctx, Self> {
+        ArraySlice {
+            num_elements: count,
+            pointer: Pointer {
+                element: *self,
+                value: ctx
+                    .builder
+                    .build_array_alloca(self.get_llvm_type(ctx.ctx), count.0, name)
+                    .unwrap(),
+            },
+        }
+    }
+
+    /// Do [`CodeGenerator::gen_var_alloc`] with the LLVM type of this [`Model<'ctx>`].
+    fn var_alloc<G: CodeGenerator + ?Sized>(
+        &self,
+        generator: &mut G,
+        ctx: &mut CodeGenContext<'ctx, '_>,
+        name: Option<&str>,
+    ) -> Result<Pointer<'ctx, Self>, String> {
+        let value = generator.gen_var_alloc(ctx, self.get_llvm_type(ctx.ctx), name)?;
+        Ok(Pointer { element: *self, value })
+    }
+
+    /// Do [`CodeGenerator::gen_array_var_alloc`] with the LLVM type of this [`Model<'ctx>`].
+    fn array_var_alloc<G: CodeGenerator + ?Sized>(
+        &self,
+        generator: &mut G,
+        ctx: &mut CodeGenContext<'ctx, '_>,
+        size: Int<'ctx>,
+        name: Option<&'ctx str>,
+    ) -> Result<Pointer<'ctx, Self>, String> {
+        let slice =
+            generator.gen_array_var_alloc(ctx, self.get_llvm_type(ctx.ctx), size.0, name)?;
+        let ptr = PointerValue::from(slice); // TODO: Remove ArraySliceValue
+
+        Ok(Pointer { element: *self, value: ptr })
+    }
+}

nac3core/src/codegen/model/fixed_int.rs

@@ -0,0 +1,156 @@
+use inkwell::{
+    context::Context,
+    types::{BasicType, BasicTypeEnum, IntType},
+    values::{BasicValue, BasicValueEnum, IntValue},
+};
+
+use super::{
+    core::*,
+    int_util::{check_int_llvm_type, review_int_llvm_value},
+    Int, IntModel,
+};
+
+/// A marker trait to mark a singleton struct that describes a particular fixed integer type.
+/// See [`Bool`], [`Byte`], [`Int32`], etc.
+///
+/// The [`Default`] trait is to enable auto-instantiations.
+pub trait NIntKind: Clone + Copy + Default {
+    /// Get the [`IntType<'ctx>`] of this [`NIntKind`].
+    fn get_int_type(ctx: &Context) -> IntType<'_>;
+
+    /// Get the [`IntType<'ctx>`] of this [`NIntKind`].
+    ///
+    /// Compared to using [`NIntKind::get_int_type`], this
+    /// function does not require [`Context`].
+    fn get_bit_width() -> u32;
+}
+
+// Some pre-defined fixed integers
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct Bool;
+pub type BoolModel = NIntModel<Bool>;
+
+impl NIntKind for Bool {
+    fn get_int_type(ctx: &Context) -> IntType<'_> {
+        ctx.bool_type()
+    }
+
+    fn get_bit_width() -> u32 {
+        1
+    }
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct Byte;
+pub type ByteModel = NIntModel<Byte>;
+
+impl NIntKind for Byte {
+    fn get_int_type(ctx: &Context) -> IntType<'_> {
+        ctx.i8_type()
+    }
+
+    fn get_bit_width() -> u32 {
+        8
+    }
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct Int32;
+pub type Int32Model = NIntModel<Int32>;
+
+impl NIntKind for Int32 {
+    fn get_int_type(ctx: &Context) -> IntType<'_> {
+        ctx.i32_type()
+    }
+
+    fn get_bit_width() -> u32 {
+        32
+    }
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct Int64;
+pub type Int64Model = NIntModel<Int64>;
+
+impl NIntKind for Int64 {
+    fn get_int_type(ctx: &Context) -> IntType<'_> {
+        ctx.i64_type()
+    }
+
+    fn get_bit_width() -> u32 {
+        64
+    }
+}
+
+/// A [`Model`] representing an [`IntType<'ctx>`] of a specified bit width.
+///
+/// Also see [`IntModel`], which is less constrained than [`NIntModel`],
+/// but enables one to handle dynamic [`IntType<'ctx>`] at runtime.
+#[derive(Debug, Clone, Copy, Default)]
+pub struct NIntModel<T: NIntKind>(pub T);
+
+impl<'ctx, T: NIntKind> CanCheckLLVMType<'ctx> for NIntModel<T> {
+    fn check_llvm_type_impl(
+        &self,
+        ctx: &'ctx Context,
+        ty: BasicTypeEnum<'ctx>,
+    ) -> Result<(), String> {
+        check_int_llvm_type(ty, T::get_int_type(ctx))
+    }
+}
+
+impl<'ctx, T: NIntKind> Model<'ctx> for NIntModel<T> {
+    type Value = NInt<'ctx, T>;
+
+    fn get_llvm_type(&self, ctx: &'ctx Context) -> BasicTypeEnum<'ctx> {
+        T::get_int_type(ctx).as_basic_type_enum()
+    }
+
+    fn review_value<V: BasicValue<'ctx>>(
+        &self,
+        ctx: &'ctx Context,
+        value: V,
+    ) -> Result<Self::Value, String> {
+        let value = review_int_llvm_value(value.as_basic_value_enum(), T::get_int_type(ctx))?;
+        Ok(NInt { kind: self.0, value })
+    }
+}
+
+impl<T: NIntKind> NIntModel<T> {
+    /// "Demote" this [`NIntModel<T>`] to an [`IntModel`].
+    ///
+    /// Information about the [`NIntKind`] will be lost.
+    pub fn to_int_model(self, ctx: &Context) -> IntModel<'_> {
+        IntModel(T::get_int_type(ctx))
+    }
+
+    /// Create an unsigned constant of this [`NIntModel`].
+    pub fn constant<'ctx>(&self, ctx: &'ctx Context, value: u64) -> NInt<'ctx, T> {
+        NInt { kind: self.0, value: T::get_int_type(ctx).const_int(value, false) }
+    }
+}
+
+/// A value of [`NIntModel<'ctx>`]
+#[derive(Debug, Clone, Copy)]
+pub struct NInt<'ctx, T: NIntKind> {
+    /// The [`NIntKind`] marker of this [`NInt`]
+    pub kind: T,
+    /// The LLVM value of this [`NInt`].
+    pub value: IntValue<'ctx>,
+}
+
+impl<'ctx, T: NIntKind> ModelValue<'ctx> for NInt<'ctx, T> {
+    fn get_llvm_value(&self) -> BasicValueEnum<'ctx> {
+        self.value.as_basic_value_enum()
+    }
+}
+
+impl<'ctx, T: NIntKind> NInt<'ctx, T> {
+    /// "Demote" this [`NInt<T>`] to an [`Int`].
+    ///
+    /// Information about the [`NIntKind`] will be lost.
+    pub fn to_int(self) -> Int<'ctx> {
+        Int(self.value)
+    }
+}

nac3core/src/codegen/model/int.rs

@@ -0,0 +1,83 @@
+use inkwell::{
+    context::Context,
+    types::{BasicType, BasicTypeEnum, IntType},
+    values::{BasicValue, BasicValueEnum, IntValue},
+};
+
+use crate::codegen::{model::int_util::review_int_llvm_value, CodeGenContext};
+
+use super::{core::*, int_util::check_int_llvm_type};
+
+/// A model representing an [`IntType<'ctx>`].
+///
+/// Also see [`NIntModel`], which is more constrained than [`IntModel`]
+/// but provides more type-safe mechanisms and even auto-derivation of [`BasicTypeEnum<'ctx>`]
+/// for creating LLVM structures.
+#[derive(Debug, Clone, Copy)]
+pub struct IntModel<'ctx>(pub IntType<'ctx>);
+
+impl<'ctx> CanCheckLLVMType<'ctx> for IntModel<'ctx> {
+    fn check_llvm_type_impl(
+        &self,
+        _ctx: &'ctx Context,
+        ty: BasicTypeEnum<'ctx>,
+    ) -> Result<(), String> {
+        check_int_llvm_type(ty, self.0)
+    }
+}
+
+impl<'ctx> Model<'ctx> for IntModel<'ctx> {
+    type Value = Int<'ctx>;
+
+    fn get_llvm_type(&self, _ctx: &'ctx Context) -> BasicTypeEnum<'ctx> {
+        self.0.as_basic_type_enum()
+    }
+
+    fn review_value<V: BasicValue<'ctx>>(
+        &self,
+        _ctx: &'ctx Context,
+        value: V,
+    ) -> Result<Self::Value, String> {
+        review_int_llvm_value(value.as_basic_value_enum(), self.0).map(Int)
+    }
+}
+
+impl<'ctx> IntModel<'ctx> {
+    /// Create a constant value that inhabits this [`IntModel<'ctx>`].
+    #[must_use]
+    pub fn constant(&self, value: u64) -> Int<'ctx> {
+        Int(self.0.const_int(value, false))
+    }
+
+    /// Check if `other` is fully compatible with this [`IntModel<'ctx>`].
+    ///
+    /// This simply checks if the underlying [`IntType<'ctx>`] has
+    /// the same number of bits.
+    #[must_use]
+    pub fn same_as(&self, other: IntModel<'ctx>) -> bool {
+        // TODO: or `self.0 == other.0` would also work?
+        self.0.get_bit_width() == other.0.get_bit_width()
+    }
+}
+
+/// An inhabitant of an [`IntModel<'ctx>`]
+#[derive(Debug, Clone, Copy)]
+pub struct Int<'ctx>(pub IntValue<'ctx>);
+
+impl<'ctx> ModelValue<'ctx> for Int<'ctx> {
+    fn get_llvm_value(&self) -> BasicValueEnum<'ctx> {
+        self.0.as_basic_value_enum()
+    }
+}
+
+impl<'ctx> Int<'ctx> {
+    #[must_use]
+    pub fn signed_cast_to_int(
+        self,
+        ctx: &CodeGenContext<'ctx, '_>,
+        target_int: IntModel<'ctx>,
+        name: &str,
+    ) -> Int<'ctx> {
+        Int(ctx.builder.build_int_s_extend_or_bit_cast(self.0, target_int.0, name).unwrap())
+    }
+}

nac3core/src/codegen/model/int_util.rs

@@ -0,0 +1,39 @@
+use inkwell::{
+    types::{BasicType, BasicTypeEnum, IntType},
+    values::{BasicValueEnum, IntValue},
+};
+
+/// Helper function to check if `scrutinee` is the same as `expected_int_type`
+pub fn check_int_llvm_type<'ctx>(
+    ty: BasicTypeEnum<'ctx>,
+    expected_int_type: IntType<'ctx>,
+) -> Result<(), String> {
+    // Check if llvm_type is int type
+    let BasicTypeEnum::IntType(ty) = ty else {
+        return Err(format!("Expecting an int type but got {ty:?}"));
+    };
+
+    // Check bit width
+    if ty.get_bit_width() != expected_int_type.get_bit_width() {
+        return Err(format!(
+            "Expecting an int type of {}-bit(s) but got int type {}-bit(s)",
+            expected_int_type.get_bit_width(),
+            ty.get_bit_width()
+        ));
+    }
+
+    Ok(())
+}
+
+/// Helper function to cast `scrutinee` is into an [`IntValue<'ctx>`].
+/// The LLVM type of `scrutinee` will be checked with [`check_int_llvm_type`].
+pub fn review_int_llvm_value<'ctx>(
+    value: BasicValueEnum<'ctx>,
+    expected_int_type: IntType<'ctx>,
+) -> Result<IntValue<'ctx>, String> {
+    // Check if value is of int type, error if that is anything else
+    check_int_llvm_type(value.get_type().as_basic_type_enum(), expected_int_type)?;
+
+    // Ok, it is must be an int
+    Ok(value.into_int_value())
+}

nac3core/src/codegen/model/mod.rs

@@ -0,0 +1,16 @@
+pub mod core;
+pub mod fixed_int;
+pub mod int;
+mod int_util;
+pub mod opaque;
+pub mod pointer;
+pub mod slice;
+pub mod structure;
+
+pub use core::*;
+pub use fixed_int::*;
+pub use int::*;
+pub use opaque::*;
+pub use pointer::*;
+pub use slice::*;
+pub use structure::*;

nac3core/src/codegen/model/opaque.rs

@@ -0,0 +1,57 @@
+use inkwell::{
+    context::Context,
+    types::BasicTypeEnum,
+    values::{BasicValue, BasicValueEnum},
+};
+
+use super::*;
+
+/// A [`Model`] that holds an arbitrary [`BasicTypeEnum`].
+///
+/// Use this and [`Opaque`] when you are dealing with a [`BasicTypeEnum<'ctx>`]
+/// at runtime and there is no way to abstract your implementation
+/// with [`Model`].
+#[derive(Debug, Clone, Copy)]
+pub struct OpaqueModel<'ctx>(pub BasicTypeEnum<'ctx>);
+
+impl<'ctx> CanCheckLLVMType<'ctx> for OpaqueModel<'ctx> {
+    fn check_llvm_type_impl(
+        &self,
+        _ctx: &'ctx Context,
+        ty: BasicTypeEnum<'ctx>,
+    ) -> Result<(), String> {
+        if ty == self.0 {
+            Ok(())
+        } else {
+            Err(format!("Expecting {}, but got {}", self.0, ty))
+        }
+    }
+}
+
+impl<'ctx> Model<'ctx> for OpaqueModel<'ctx> {
+    type Value = Opaque<'ctx>;
+
+    fn get_llvm_type(&self, _ctx: &'ctx Context) -> BasicTypeEnum<'ctx> {
+        self.0
+    }
+
+    fn review_value<V: BasicValue<'ctx>>(
+        &self,
+        ctx: &'ctx Context,
+        value: V,
+    ) -> Result<Self::Value, String> {
+        let value = value.as_basic_value_enum();
+        self.check_llvm_type(ctx, value.get_type())?;
+        Ok(Opaque(value))
+    }
+}
+
+/// A value of [`OpaqueModel`]
+#[derive(Debug, Clone, Copy)]
+pub struct Opaque<'ctx>(pub BasicValueEnum<'ctx>);
+
+impl<'ctx> ModelValue<'ctx> for Opaque<'ctx> {
+    fn get_llvm_value(&self) -> BasicValueEnum<'ctx> {
+        self.0
+    }
+}

nac3core/src/codegen/model/pointer.rs

@@ -0,0 +1,94 @@
+use inkwell::{
+    context::Context,
+    types::{BasicType, BasicTypeEnum},
+    values::{BasicValue, BasicValueEnum, PointerValue},
+    AddressSpace,
+};
+
+use crate::codegen::CodeGenContext;
+
+use super::{core::*, OpaqueModel};
+
+/// A [`Model<'ctx>`] representing an LLVM [`PointerType<'ctx>`]
+/// with *full* information on the element u
+///
+/// [`self.0`] contains [`Model<'ctx>`] that represents the
+/// LLVM type of element of the [`PointerType<'ctx>`] is pointing at
+/// (like `PointerType<'ctx>::get_element_type()`, but abstracted as a [`Model<'ctx>`]).
+#[derive(Debug, Clone, Copy, Default)]
+pub struct PointerModel<E>(pub E);
+
+impl<'ctx, E: Model<'ctx>> CanCheckLLVMType<'ctx> for PointerModel<E> {
+    fn check_llvm_type_impl(
+        &self,
+        ctx: &'ctx Context,
+        ty: BasicTypeEnum<'ctx>,
+    ) -> Result<(), String> {
+        // Check if scrutinee is even a PointerValue
+        let BasicTypeEnum::PointerType(ty) = ty else {
+            return Err(format!("Expecting a pointer value, but got {ty:?}"));
+        };
+
+        // Check the type of what the pointer is pointing at
+        // TODO: This will be deprecated by inkwell > llvm14 because `get_element_type()` will be gone
+        let Ok(element_ty) = BasicTypeEnum::try_from(ty.get_element_type()) else {
+            return Err(format!(
+                "Expecting pointer to point to an inkwell BasicValue, but got {ty:?}"
+            ));
+        };
+
+        self.0.check_llvm_type(ctx, element_ty) // TODO: Include backtrace?
+    }
+}
+
+impl<'ctx, E: Model<'ctx>> Model<'ctx> for PointerModel<E> {
+    type Value = Pointer<'ctx, E>;
+
+    fn get_llvm_type(&self, ctx: &'ctx Context) -> BasicTypeEnum<'ctx> {
+        self.0.get_llvm_type(ctx).ptr_type(AddressSpace::default()).as_basic_type_enum()
+    }
+
+    fn review_value<V: BasicValue<'ctx>>(
+        &self,
+        ctx: &'ctx Context,
+        value: V,
+    ) -> Result<Self::Value, String> {
+        let value = value.as_basic_value_enum();
+
+        self.check_llvm_type(ctx, value.get_type())?;
+
+        // TODO: Check get_element_type(). For inkwell LLVM 14 at least...
+        Ok(Pointer { element: self.0, value: value.into_pointer_value() })
+    }
+}
+
+/// An inhabitant of [`PointerModel<E>`]
+#[derive(Debug, Clone, Copy)]
+pub struct Pointer<'ctx, E: Model<'ctx>> {
+    pub element: E,
+    pub value: PointerValue<'ctx>,
+}
+
+impl<'ctx, E: Model<'ctx>> ModelValue<'ctx> for Pointer<'ctx, E> {
+    fn get_llvm_value(&self) -> BasicValueEnum<'ctx> {
+        self.value.as_basic_value_enum()
+    }
+}
+
+impl<'ctx, E: Model<'ctx>> Pointer<'ctx, E> {
+    /// Build an instruction to store a value into this pointer
+    pub fn store(&self, ctx: &CodeGenContext<'ctx, '_>, val: E::Value) {
+        ctx.builder.build_store(self.value, val.get_llvm_value()).unwrap();
+    }
+
+    /// Build an instruction to load a value from this pointer
+    pub fn load(&self, ctx: &CodeGenContext<'ctx, '_>, name: &str) -> E::Value {
+        let val = ctx.builder.build_load(self.value, name).unwrap();
+        self.element.review_value(ctx.ctx, val).unwrap() // If unwrap() panics, there is a logic error in your code.
+    }
+
+    /// "Demote" the [`Model`] of the thing this pointer is pointing at.
+    pub fn to_opaque(self, ctx: &'ctx Context) -> Pointer<'ctx, OpaqueModel<'ctx>> {
+        Pointer { element: OpaqueModel(self.element.get_llvm_type(ctx)), value: self.value }
+    }
+}

nac3core/src/codegen/model/slice.rs

@@ -0,0 +1,87 @@
+use crate::codegen::{CodeGenContext, CodeGenerator};
+
+use super::{Int, Model, Pointer};
+
+/// An LLVM "slice" - literally just a pointer and a length value.
+/// The pointer points to a location with `num_elements` **contiguously** placed
+/// values of [`E`][`Model<ctx>`] in memory.
+///
+/// NOTE: This is NOT a [`Model`]! This is simply a helper
+/// structure to aggregate a length value and a pointer together.
+pub struct ArraySlice<'ctx, E: Model<'ctx>> {
+    pub pointer: Pointer<'ctx, E>,
+    pub num_elements: Int<'ctx>,
+}
+
+impl<'ctx, E: Model<'ctx>> ArraySlice<'ctx, E> {
+    /// Get the `idx`-nth element of this [`ArraySlice`],
+    /// but doesn't do an assertion to see if `idx` is
+    /// out of bounds or not.
+    ///
+    /// Also see [`ArraySlice::ix`].
+    pub fn ix_unchecked(
+        &self,
+        ctx: &CodeGenContext<'ctx, '_>,
+        idx: Int<'ctx>,
+        name: &str,
+    ) -> Pointer<'ctx, E> {
+        let element_addr =
+            unsafe { ctx.builder.build_in_bounds_gep(self.pointer.value, &[idx.0], name).unwrap() };
+        Pointer { value: element_addr, element: self.pointer.element }
+    }
+
+    /// Call [`ArraySlice::ix_unchecked`], but
+    /// checks if `idx` is in bounds, otherwise
+    /// a runtime `IndexError` will be thrown.
+    pub fn ix<G: CodeGenerator + ?Sized>(
+        &self,
+        generator: &mut G,
+        ctx: &mut CodeGenContext<'ctx, '_>,
+        idx: Int<'ctx>,
+        name: &str,
+    ) -> Pointer<'ctx, E> {
+        let int_type = self.num_elements.0.get_type(); // NOTE: Weird get_type(), see comment under `trait Ixed`
+
+        assert_eq!(int_type.get_bit_width(), idx.0.get_type().get_bit_width()); // Might as well check bit width to catch bugs
+
+        // TODO: SGE or UGE? or make it defined by the implementee?
+
+        // Check `0 <= index`
+        let lower_bounded = ctx
+            .builder
+            .build_int_compare(
+                inkwell::IntPredicate::SLE,
+                int_type.const_zero(),
+                idx.0,
+                "lower_bounded",
+            )
+            .unwrap();
+
+        // Check `index < num_elements`
+        let upper_bounded = ctx
+            .builder
+            .build_int_compare(
+                inkwell::IntPredicate::SLT,
+                idx.0,
+                self.num_elements.0,
+                "upper_bounded",
+            )
+            .unwrap();
+
+        // Compute `0 <= index && index < num_elements`
+        let bounded = ctx.builder.build_and(lower_bounded, upper_bounded, "bounded").unwrap();
+
+        // Assert `bounded`
+        ctx.make_assert(
+            generator,
+            bounded,
+            "0:IndexError",
+            "nac3core LLVM codegen attempting to access out of bounds array index {0}. Must satisfy 0 <= index < {2}",
+            [ Some(idx.0), Some(self.num_elements.0), None],
+            ctx.current_loc
+        );
+
+        // ...and finally do indexing
+        self.ix_unchecked(ctx, idx, name)
+    }
+}

nac3core/src/codegen/model/structure.rs

@@ -0,0 +1,396 @@
+use inkwell::{
+    context::Context,
+    types::{BasicType, BasicTypeEnum, StructType},
+    values::{BasicValue, BasicValueEnum, StructValue},
+};
+use itertools::{izip, Itertools};
+
+use crate::codegen::CodeGenContext;
+
+use super::{core::CanCheckLLVMType, Model, ModelValue, Pointer};
+
+/// An LLVM struct's "field".
+#[derive(Debug, Clone, Copy)]
+pub struct Field<E> {
+    /// The GEP index of the field.
+    pub gep_index: u64,
+
+    /// The name of this field. Generally named
+    /// to how the field is named in ARTIQ or IRRT.
+    ///
+    /// NOTE: This is only used for debugging.
+    pub name: &'static str,
+
+    /// The [`Model`] of the field.
+    pub element: E,
+}
+
+// A helper struct for [`FieldBuilder`]
+struct FieldLLVM<'ctx> {
+    gep_index: u64,
+    name: &'ctx str,
+
+    // Only CanCheckLLVMType is needed, dont use `Model<'ctx>`
+    llvm_type_model: Box<dyn CanCheckLLVMType<'ctx> + 'ctx>,
+    llvm_type: BasicTypeEnum<'ctx>,
+}
+
+/// A helper struct to create [`Field`]-s in [`StructKind::build_fields`].
+///
+/// See [`StructKind`] for more details and see how [`FieldBuilder`] is put
+/// into action.
+pub struct FieldBuilder<'ctx> {
+    /// The [`Context`] this [`FieldBuilder`] is under.
+    ///
+    /// Can be used in [`StructKind::build_fields`].
+    /// See [`StructKind`] for more details and see how [`FieldBuilder`] is put
+    /// into action.
+    pub ctx: &'ctx Context,
+
+    /// An incrementing counter for GEP indices when
+    /// doing [`FieldBuilder::add_field`] or [`FieldBuilder::add_field_auto`].
+    gep_index_counter: u64,
+
+    /// Name of the `struct` this [`FieldBuilder`] is currently
+    /// building.
+    ///
+    /// NOTE: This is only used for debugging.
+    struct_name: &'ctx str,
+
+    /// The fields added so far.
+    fields: Vec<FieldLLVM<'ctx>>,
+}
+
+impl<'ctx> FieldBuilder<'ctx> {
+    #[must_use]
+    pub fn new(ctx: &'ctx Context, struct_name: &'ctx str) -> Self {
+        FieldBuilder { ctx, gep_index_counter: 0, struct_name, fields: Vec::new() }
+    }
+
+    fn next_gep_index(&mut self) -> u64 {
+        let index = self.gep_index_counter;
+        self.gep_index_counter += 1;
+        index
+    }
+
+    /// Add a new field.
+    ///
+    /// - `name`: The name of the field. See [`Field::name`].
+    /// - `element`: The [`Model`] of the type of the field. See [`Field::element`].
+    pub fn add_field<E: Model<'ctx> + 'ctx>(&mut self, name: &'static str, element: E) -> Field<E> {
+        let gep_index = self.next_gep_index();
+
+        self.fields.push(FieldLLVM {
+            gep_index,
+            name,
+            llvm_type: element.get_llvm_type(self.ctx),
+            llvm_type_model: Box::new(element),
+        });
+
+        Field { gep_index, name, element }
+    }
+
+    /// Like [`FieldBuilder::add_field`] but `element` can be **automatically derived**
+    /// if it has the `Default` instance.
+    ///
+    /// Certain [`Model`] has a [`Default`] trait - [`Model`]s that are just singletons,
+    /// By deriving the [`Default`] trait on those [`Model`]s, Rust could automatically
+    /// construct the [`Model`] with [`Default::default`].
+    ///
+    /// This function is equivalent to
+    /// ```ignore
+    /// self.add_field(name, E::default())
+    /// ```
+    pub fn add_field_auto<E: Model<'ctx> + Default + 'ctx>(
+        &mut self,
+        name: &'static str,
+    ) -> Field<E> {
+        self.add_field(name, E::default())
+    }
+}
+
+/// A marker trait to mark singleton struct that
+/// describes a particular LLVM structure.
+///
+/// It is a powerful inkwell abstraction that can reduce
+/// a lot of inkwell boilerplate when dealing with LLVM structs,
+/// `getelementptr`, `load`-ing and `store`-ing fields.
+///
+/// ### Usage
+pub trait StructKind<'ctx>: Clone + Copy {
+    /// The type of the Rust `struct` that holds all the fields of this LLVM struct.
+    type Fields;
+
+    // TODO:
+    /// The name of this [`StructKind`].
+    ///
+    /// The name should be the name of in
+    /// IRRT's `struct` or ARTIQ's definition.
+    fn struct_name(&self) -> &'static str;
+
+    /// Define the [`Field`]s of this [`StructKind`]
+    ///
+    ///
+    /// ### Syntax
+    ///
+    /// Suppose you want to define the following C++ `struct`s in `nac3core`:
+    /// ```cpp
+    /// template <typename SizeT>
+    /// struct Str {
+    ///     uint8_t* content; // NOTE: could be `void *`
+    ///     SizeT length;
+    /// }
+    ///
+    /// template <typename SizeT>
+    /// struct Exception {
+    ///     uint32_t id;
+    ///     Str message;
+    ///     uint64_t param0;
+    ///     uint64_t param1;
+    ///     uint64_t param2;
+    /// }
+    /// ```
+    ///
+    /// You write this in nac3core:
+    /// ```ignore
+    /// struct Str<'ctx> {
+    ///     sizet: IntModel<'ctx>,
+    /// }
+    ///
+    /// struct StrFields<'ctx> {
+    ///     content: Field<PointerModel<ByteModel>>, // equivalent to `NIntModel<Byte>`.
+    ///     length: Field<IntModel<'ctx>>, // `SizeT` is only known in runtime - `CodeGenerator::get_size_type()`.  /// }
+    /// }
+    ///
+    /// impl StructKind<'ctx> for Str<'ctx> {
+    ///     fn struct_name() {
+    ///         "Str"
+    ///     }
+    ///
+    ///     fn build_fields(&self, builder: &mut FieldBuilder<'ctx>) -> Self::Fields {
+    ///         // THE order of `builder.add_field*` is IMPORTANT!!!
+    ///         // so the GEP indices would be correct.
+    ///         StrFields {
+    ///             content: builder.add_field_auto("content"), // `PointerModel<ByteModel>` has `Default` trait.
+    ///             length: builder.add_field("length", IntModel(self.sizet)), // `PointerModel<ByteModel>` has `Default` trait.
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// struct Exception<'ctx> {
+    ///     sizet: IntModel<'ctx>,
+    /// }
+    ///
+    /// struct ExceptionFields<'ctx> {
+    ///     id: Field<NIntModel<Int32>>,
+    ///     message: Field<StructModel<Str>>,
+    ///     param0: Field<NIntModel<Int64>>,
+    ///     param1: Field<NIntModel<Int64>>,
+    ///     param2: Field<NIntModel<Int64>>,
+    /// }
+    ///
+    /// impl StructKind<'ctx> for Exception<'ctx> {
+    ///     fn struct_name() {
+    ///         "Exception"
+    ///     }
+    ///
+    ///     fn build_fields(&self, builder: &mut FieldBuilder<'ctx>) -> Self::Fields {
+    ///         // THE order of `builder.add_field*` is IMPORTANT!!!
+    ///         // so the GEP indices would be correct.
+    ///         ExceptionFields {
+    ///             id: builder.add_field_auto("content"), // `NIntModel<Int32>` has `Default` trait.
+    ///             message: builder.add_field("message", StructModel(Str { sizet: self.sizet })),
+    ///             param0: builder.add_field_auto("param0"), // has `Default` trait
+    ///             param1: builder.add_field_auto("param1"), // has `Default` trait
+    ///             param2: builder.add_field_auto("param2"), // has `Default` trait
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// Then to `alloca` an `Exception`, do this:
+    /// ```ignore
+    /// let generator: dyn CodeGenerator<'ctx>;
+    /// let ctx: &CodeGenContext<'ctx, '_>;
+    /// let sizet = generator.get_size_type();
+    /// let exn_model = StructModel(Exception { sizet });
+    /// let exn = exn_model.alloca(ctx, "my_exception"); // Every [`Model<'ctx>`] has an `.alloca()` function.
+    /// // exn: Pointer<'ctx, StructModel<Exception>>
+    /// ```
+    ///
+    /// NOTE: In fact, it is possible to define `Str` and `Exception` like this:
+    /// ```ignore
+    /// struct Str<SizeT: NIntModel> {
+    ///     _phantom: PhantomData<SizeT>,
+    /// }
+    ///
+    /// struct Exception<T: NIntModel> {
+    ///     _phantom: PhantomData<SizeT>,
+    /// }
+    /// ```
+    /// But issues arise by you don't know the nac3core
+    /// `CodeGenerator`'s `get_size_type()` before hand.
+    fn build_fields(&self, builder: &mut FieldBuilder<'ctx>) -> Self::Fields;
+}
+
+/// A [`Model<'ctx>`] that represents an LLVM struct.
+///
+/// `self.0` contains a [`IsStruct<'ctx>`] that gives the details of the LLVM struct.
+#[derive(Debug, Clone, Copy, Default)]
+pub struct StructModel<S>(pub S);
+
+impl<'ctx, S: StructKind<'ctx>> CanCheckLLVMType<'ctx> for StructModel<S> {
+    fn check_llvm_type_impl(
+        &self,
+        ctx: &'ctx Context,
+        ty: BasicTypeEnum<'ctx>,
+    ) -> Result<(), String> {
+        // Check if scrutinee is even a struct type
+        let BasicTypeEnum::StructType(ty) = ty else {
+            return Err(format!("Expecting a struct type, but got {ty:?}"));
+        };
+
+        // Ok. now check the struct type thoroughly
+        self.check_struct_type(ctx, ty)
+    }
+}
+
+impl<'ctx, S: StructKind<'ctx>> Model<'ctx> for StructModel<S> {
+    type Value = Struct<'ctx, S>;
+
+    fn get_llvm_type(&self, ctx: &'ctx Context) -> BasicTypeEnum<'ctx> {
+        self.get_struct_type(ctx).as_basic_type_enum()
+    }
+
+    fn review_value<V: BasicValue<'ctx>>(
+        &self,
+        ctx: &'ctx Context,
+        value: V,
+    ) -> Result<Self::Value, String> {
+        let value = value.as_basic_value_enum();
+
+        // Check that `value` is not some bogus values or an incorrect StructValue
+        self.check_llvm_type(ctx, value.get_type())?;
+
+        Ok(Struct { kind: self.0, value: value.into_struct_value() })
+    }
+}
+
+impl<'ctx, S: StructKind<'ctx>> StructModel<S> {
+    /// Get the [`S::Fields`] of this [`StructModel`].
+    pub fn get_fields(&self, ctx: &'ctx Context) -> S::Fields {
+        let mut builder = FieldBuilder::new(ctx, self.0.struct_name());
+        self.0.build_fields(&mut builder)
+    }
+
+    /// Get the LLVM struct type this [`IsStruct<'ctx>`] is representing.
+    pub fn get_struct_type(&self, ctx: &'ctx Context) -> StructType<'ctx> {
+        let mut builder = FieldBuilder::new(ctx, self.0.struct_name());
+        self.0.build_fields(&mut builder); // Self::Fields is discarded
+
+        let field_types = builder.fields.iter().map(|f| f.llvm_type).collect_vec();
+        ctx.struct_type(&field_types, false)
+    }
+
+    /// Check if `scrutinee` matches the [`StructType<'ctx>`] this [`IsStruct<'ctx>`] is representing.
+    pub fn check_struct_type(
+        &self,
+        ctx: &'ctx Context,
+        scrutinee: StructType<'ctx>,
+    ) -> Result<(), String> {
+        // Details about scrutinee
+        let scrutinee_field_types = scrutinee.get_field_types();
+
+        // Details about the defined specifications of this struct
+        // We will access them through builder
+        let mut builder = FieldBuilder::new(ctx, self.0.struct_name());
+        self.0.build_fields(&mut builder);
+
+        // Check # of fields
+        if builder.fields.len() != scrutinee_field_types.len() {
+            return Err(format!(
+                "Expecting struct to have {} field(s), but scrutinee has {} field(s)",
+                builder.fields.len(),
+                scrutinee_field_types.len()
+            ));
+        }
+
+        // Check the types of each field
+        // TODO: Traceback?
+        for (f, scrutinee_field_type) in izip!(builder.fields, scrutinee_field_types) {
+            f.llvm_type_model
+                .check_llvm_type_impl(ctx, scrutinee_field_type.as_basic_type_enum())?;
+        }
+
+        Ok(())
+    }
+}
+
+/// A value of [`StructModel<S>`] of a particular [`StructKind`].
+#[derive(Debug, Clone, Copy)]
+pub struct Struct<'ctx, S> {
+    pub kind: S,
+    pub value: StructValue<'ctx>,
+}
+
+impl<'ctx, S: StructKind<'ctx>> ModelValue<'ctx> for Struct<'ctx, S> {
+    fn get_llvm_value(&self) -> BasicValueEnum<'ctx> {
+        self.value.as_basic_value_enum()
+    }
+}
+
+impl<'ctx, S: StructKind<'ctx>> Pointer<'ctx, StructModel<S>> {
+    /// Build an instruction that does `getelementptr` on an LLVM structure referenced by this pointer.
+    ///
+    /// This provides a nice syntax to chain up `getelementptr` in an intuitive and type-safe way:
+    ///
+    /// ```ignore
+    /// let ctx: &CodeGenContext<'ctx, '_>;
+    /// let ndarray: Pointer<'ctx, StructModel<NpArray<'ctx>>>;
+    /// ndarray.gep(ctx, |f| f.ndims).store();
+    /// ```
+    ///
+    /// You might even write chains `gep`, i.e.,
+    /// ```ignore
+    /// let exn_ptr: Pointer<'ctx, StructModel<Exception>>;
+    /// let value: Int<'ctx>; // Suppose it has the correct inkwell `IntType<'ctx>`.
+    ///
+    /// // To do `exn.message.length = value`:
+    /// let exn_message_ptr = exn_ptr.gep(ctx, |f| f.message);
+    /// let exn_message_length_ptr = exn_message_ptr.gep(ctx, |f| f.length);
+    /// exn_message_length_ptr.store(ctx, my_value);
+    ///
+    /// // or simply:
+    /// exn_ptr
+    ///     .gep(ctx, |f| f.message)
+    ///     .gep(ctx, |f| f.length)
+    ///     .store(ctx, my_value) // Equivalent to `my_struct.thing1.value = my_value`
+    /// ```
+    pub fn gep<E, GetFieldFn>(
+        &self,
+        ctx: &CodeGenContext<'ctx, '_>,
+        get_field: GetFieldFn,
+    ) -> Pointer<'ctx, E>
+    where
+        E: Model<'ctx>,
+        GetFieldFn: FnOnce(S::Fields) -> Field<E>,
+    {
+        let fields = self.element.get_fields(ctx.ctx);
+        let field = get_field(fields);
+
+        // TODO: I think I'm not supposed to *just* use i32 for GEP like that
+        let llvm_i32 = ctx.ctx.i32_type();
+
+        let ptr = unsafe {
+            ctx.builder
+                .build_in_bounds_gep(
+                    self.value,
+                    &[llvm_i32.const_zero(), llvm_i32.const_int(field.gep_index, false)],
+                    field.name,
+                )
+                .unwrap()
+        };
+
+        Pointer { element: field.element, value: ptr }
+    }
+}