diff --git a/nac3core/src/codegen/model/function_builder.rs b/nac3core/src/codegen/model/function_builder.rs
new file mode 100644
index 00000000..fcc3748b
--- /dev/null
+++ b/nac3core/src/codegen/model/function_builder.rs
@@ -0,0 +1,62 @@
+use inkwell::{
+    types::{BasicMetadataTypeEnum, BasicType},
+    values::{AnyValue, BasicMetadataValueEnum, BasicValueEnum},
+};
+
+use crate::codegen::{model::*, CodeGenContext};
+
+// TODO: Variadic argument?
+pub struct FunctionBuilder<'ctx, 'a> {
+    ctx: &'a CodeGenContext<'ctx, 'a>,
+    fn_name: &'a str,
+    arguments: Vec<(BasicMetadataTypeEnum<'ctx>, BasicMetadataValueEnum<'ctx>)>,
+}
+
+impl<'ctx, 'a> FunctionBuilder<'ctx, 'a> {
+    pub fn begin(ctx: &'a CodeGenContext<'ctx, 'a>, fn_name: &'a str) -> Self {
+        FunctionBuilder { ctx, fn_name, arguments: Vec::new() }
+    }
+
+    // NOTE: `_name` is for self-documentation
+    #[must_use]
+    pub fn arg<M: Model<'ctx>>(mut self, _name: &'static str, model: M, value: M::Value) -> Self {
+        model.check_value(self.ctx.ctx, value).unwrap(); // Panics if the passed `value` has the incorrect type.
+
+        self.arguments
+            .push((model.get_llvm_type(self.ctx.ctx).into(), value.get_llvm_value().into()));
+        self
+    }
+
+    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();
+
+        // Get the LLVM function, create (by declaring) the function if it doesn't exist in `ctx.module`.
+        let function = self.ctx.module.get_function(self.fn_name).unwrap_or_else(|| {
+            let return_type = return_model.get_llvm_type(self.ctx.ctx);
+            let fn_type = return_type.fn_type(&param_tys, false);
+            self.ctx.module.add_function(self.fn_name, fn_type, None)
+        });
+
+        // Build call
+        let ret = self.ctx.builder.build_call(function, &param_vals, name).unwrap();
+
+        // Check the return value/type
+        let Ok(ret) = BasicValueEnum::try_from(ret.as_any_value_enum()) else {
+            panic!("Return type is not a BasicValue");
+        };
+        return_model.review_value(self.ctx.ctx, ret).unwrap()
+    }
+
+    // TODO: Code duplication, but otherwise returning<S: Optic<'ctx>> cannot resolve S if return_optic = None
+    pub fn returning_void(self) {
+        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(|| {
+            let return_type = self.ctx.ctx.void_type();
+            let fn_type = return_type.fn_type(&param_tys, false);
+            self.ctx.module.add_function(self.fn_name, fn_type, None)
+        });
+
+        self.ctx.builder.build_call(function, &param_vals, "").unwrap();
+    }
+}
diff --git a/nac3core/src/codegen/model/mod.rs b/nac3core/src/codegen/model/mod.rs
index 2ebf02b8..0520b530 100644
--- a/nac3core/src/codegen/model/mod.rs
+++ b/nac3core/src/codegen/model/mod.rs
@@ -1,5 +1,6 @@
 pub mod core;
 pub mod fixed_int;
+pub mod function_builder;
 pub mod int;
 mod int_util;
 pub mod opaque;