diff --git a/Cargo.lock b/Cargo.lock
index fbabf72..897a276 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -248,10 +248,17 @@ dependencies = [
  "anyhow",
  "indoc",
  "parser",
+ "pretty_assertions",
  "quick-error",
  "tokenizer",
 ]
 
+[[package]]
+name = "diff"
+version = "0.1.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56254986775e3233ffa9c4d7d3faaf6d36a2c09d30b20687e9f88bc8bafc16c8"
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -478,6 +485,16 @@ dependencies = [
  "zerocopy",
 ]
 
+[[package]]
+name = "pretty_assertions"
+version = "1.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ae130e2f271fbc2ac3a40fb1d07180839cdbbe443c7a27e1e3c13c5cac0116d"
+dependencies = [
+ "diff",
+ "yansi",
+]
+
 [[package]]
 name = "prettyplease"
 version = "0.1.25"
@@ -1046,6 +1063,12 @@ dependencies = [
  "tap",
 ]
 
+[[package]]
+name = "yansi"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cfe53a6657fd280eaa890a3bc59152892ffa3e30101319d168b781ed6529b049"
+
 [[package]]
 name = "zerocopy"
 version = "0.8.27"
diff --git a/libs/compiler/Cargo.toml b/libs/compiler/Cargo.toml
index 122c21c..85434ac 100644
--- a/libs/compiler/Cargo.toml
+++ b/libs/compiler/Cargo.toml
@@ -11,3 +11,4 @@ tokenizer = { path = "../tokenizer" }
 [dev-dependencies]
 anyhow = { version = "1.0" }
 indoc = { version = "2.0" }
+pretty_assertions = "1"
diff --git a/libs/compiler/src/lib.rs b/libs/compiler/src/lib.rs
index 4d1d570..388d2b2 100644
--- a/libs/compiler/src/lib.rs
+++ b/libs/compiler/src/lib.rs
@@ -11,7 +11,7 @@ use std::cmp::Ordering;
 use std::collections::HashMap;
 use std::io::{BufWriter, Write};
 
-pub use v2::{Compiler, Error};
+pub use v2::{Compiler, CompilerConfig, Error};
 
 quick_error! {
     #[derive(Debug)]
diff --git a/libs/compiler/src/test/declaration_function_invocation.rs b/libs/compiler/src/test/declaration_function_invocation.rs
new file mode 100644
index 0000000..1b1a05c
--- /dev/null
+++ b/libs/compiler/src/test/declaration_function_invocation.rs
@@ -0,0 +1,85 @@
+use crate::compile;
+use indoc::indoc;
+use pretty_assertions::assert_eq;
+
+#[test]
+fn no_arguments() -> anyhow::Result<()> {
+    let compiled = compile! {
+        debug
+        "
+        fn doSomething() {};
+        let i = doSomething();
+        "
+    };
+
+    let to_test = indoc! {
+        "
+        j main
+        doSomething:
+        push ra
+        sub r0 sp 1
+        get ra db r0
+        sub sp sp 1
+        j ra
+        main:
+        jal doSomething
+        move r8 r15 #i
+        "
+    };
+
+    assert_eq!(compiled, to_test);
+
+    Ok(())
+}
+
+#[test]
+fn let_var_args() -> anyhow::Result<()> {
+    let compiled = compile! {
+        debug
+        "
+        fn doSomething(arg1) {};
+        let arg1 = 123;
+        let i = doSomething(arg1);
+        "
+    };
+
+    assert_eq!(
+        compiled,
+        indoc! {
+            "
+            j main
+            doSomething:
+            pop r8 #arg1
+            push ra
+            sub r0 sp 1
+            get ra db r0
+            sub sp sp 1
+            j ra
+            main:
+            move r8 123 #arg1
+            push r8
+            push r8
+            jal doSomething
+            sub r0 sp 1
+            get r8 db r0
+            sub sp sp 1
+            move r9 r15 #i
+            "
+        }
+    );
+
+    Ok(())
+}
+
+#[test]
+fn incorrect_args_count() -> anyhow::Result<()> {
+    let compiled = compile! {
+        debug
+        "
+        fn doSomething(arg1, arg2){};
+        let i = doSomething();
+        "
+    };
+
+    Ok(())
+}
diff --git a/libs/compiler/src/test/declaration_literal.rs b/libs/compiler/src/test/declaration_literal.rs
new file mode 100644
index 0000000..5a881a4
--- /dev/null
+++ b/libs/compiler/src/test/declaration_literal.rs
@@ -0,0 +1,62 @@
+use indoc::indoc;
+use pretty_assertions::assert_eq;
+
+#[test]
+fn variable_declaration_numeric_literal() -> anyhow::Result<()> {
+    let compiled = crate::compile! {
+        debug r#"
+            let i = 20c;
+        "#
+    };
+
+    assert_eq!(
+        compiled,
+        indoc! {
+            "
+            j main
+            main:
+            move r8 293.15 #i
+            "
+        }
+    );
+
+    Ok(())
+}
+
+#[test]
+fn variable_declaration_numeric_literal_stack_spillover() -> anyhow::Result<()> {
+    let compiled = compile! {debug r#"
+        let a = 0;
+        let b = 1;
+        let c = 2;
+        let d = 3;
+        let e = 4;
+        let f = 5;
+        let g = 6;
+        let h = 7;
+        let i = 8;
+        let j = 9;
+    "#};
+
+    assert_eq!(
+        compiled,
+        indoc! {
+            "
+            j main
+            main:
+            move r8 0 #a
+            move r9 1 #b
+            move r10 2 #c
+            move r11 3 #d
+            move r12 4 #e
+            move r13 5 #f
+            move r14 6 #g
+            push 7 #h
+            push 8 #i
+            push 9 #j
+            "
+        }
+    );
+
+    Ok(())
+}
diff --git a/libs/compiler/src/test/function_declaration.rs b/libs/compiler/src/test/function_declaration.rs
new file mode 100644
index 0000000..28200f7
--- /dev/null
+++ b/libs/compiler/src/test/function_declaration.rs
@@ -0,0 +1,58 @@
+use indoc::indoc;
+use pretty_assertions::assert_eq;
+
+#[test]
+fn test_function_declaration_with_spillover_params() -> anyhow::Result<()> {
+    let compiled = compile!(debug r#"
+        // we need more than 4 params to 'spill' into a stack var
+        fn doSomething(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9) {};
+    "#);
+
+    assert_eq!(
+        compiled,
+        indoc! {"
+            j main
+            doSomething:
+            pop r8 #arg9
+            pop r9 #arg8
+            pop r10 #arg7
+            pop r11 #arg6
+            pop r12 #arg5
+            pop r13 #arg4
+            pop r14 #arg3
+            push ra
+            sub r0 sp 1
+            get ra db r0
+            sub sp sp 3
+            j ra
+        "}
+    );
+
+    Ok(())
+}
+
+#[test]
+fn test_function_declaration_with_register_params() -> anyhow::Result<()> {
+    let compiled = compile!(debug r#"
+        // This is a test function declaration with no body
+        fn doSomething(arg1, arg2) {
+        };
+    "#);
+
+    assert_eq!(
+        compiled,
+        indoc! {"
+            j main
+            doSomething:
+            pop r8 #arg2
+            pop r9 #arg1
+            push ra
+            sub r0 sp 1
+            get ra db r0
+            sub sp sp 1
+            j ra
+        "}
+    );
+
+    Ok(())
+}
diff --git a/libs/compiler/src/test/mod.rs b/libs/compiler/src/test/mod.rs
index 4321378..e439f4d 100644
--- a/libs/compiler/src/test/mod.rs
+++ b/libs/compiler/src/test/mod.rs
@@ -1,21 +1,15 @@
-use super::v2::Compiler;
-use crate::v2::CompilerConfig;
-use indoc::indoc;
-use parser::Parser;
-use std::io::BufWriter;
-use tokenizer::Tokenizer;
-
 macro_rules! output {
     ($input:expr) => {
         String::from_utf8($input.into_inner()?)?
     };
 }
 
+#[macro_export]
 macro_rules! compile {
     ($source:expr) => {{
-        let mut writer = BufWriter::new(Vec::new());
-        let compiler = Compiler::new(
-            Parser::new(Tokenizer::from(String::from($source))),
+        let mut writer = std::io::BufWriter::new(Vec::new());
+        let compiler = crate::Compiler::new(
+            parser::Parser::new(tokenizer::Tokenizer::from(String::from($source))),
             &mut writer,
             None,
         );
@@ -24,73 +18,16 @@ macro_rules! compile {
     }};
 
     (debug $source:expr) => {{
-        let mut writer = BufWriter::new(Vec::new());
-        let compiler = Compiler::new(
-            Parser::new(Tokenizer::from(String::from($source))),
+        let mut writer = std::io::BufWriter::new(Vec::new());
+        let compiler = crate::Compiler::new(
+            parser::Parser::new(tokenizer::Tokenizer::from(String::from($source))),
             &mut writer,
-            Some(CompilerConfig {
-                debug: true,
-                ..Default::default()
-            }),
+            Some(crate::CompilerConfig { debug: true }),
         );
         compiler.compile()?;
         output!(writer)
     }};
 }
-
-#[test]
-fn test_function_declaration_with_spillover_params() -> anyhow::Result<()> {
-    let compiled = compile!(debug r#"
-        // we need more than 4 params to 'spill' into a stack var
-        fn doSomething(arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9) {};
-    "#);
-
-    assert_eq!(
-        compiled,
-        indoc! {"
-            j main
-            doSomething:
-            pop r8 #arg9
-            pop r9 #arg8
-            pop r10 #arg7
-            pop r11 #arg6
-            pop r12 #arg5
-            pop r13 #arg4
-            pop r14 #arg3
-            pop r15 #arg2
-            push ra
-            sub r0 sp 1
-            get ra db r0
-            sub sp sp 2
-            j ra
-        "}
-    );
-
-    Ok(())
-}
-
-#[test]
-fn test_function_declaration_with_register_params() -> anyhow::Result<()> {
-    let compiled = compile!(debug r#"
-        // This is a test function declaration with no body
-        fn doSomething(arg1, arg2) {
-        };
-    "#);
-
-    assert_eq!(
-        compiled,
-        indoc! {"
-            j main
-            doSomething:
-            pop r8 #arg2
-            pop r9 #arg1
-            push ra
-            sub r0 sp 1
-            get ra db r0
-            sub sp sp 1
-            j ra
-        "}
-    );
-
-    Ok(())
-}
+mod declaration_function_invocation;
+mod declaration_literal;
+mod function_declaration;
diff --git a/libs/compiler/src/v2.rs b/libs/compiler/src/v2.rs
index b184c8b..c411d8c 100644
--- a/libs/compiler/src/v2.rs
+++ b/libs/compiler/src/v2.rs
@@ -1,7 +1,10 @@
 use crate::variable_manager::{self, LocationRequest, VariableLocation, VariableScope};
 use parser::{
     Parser as ASTParser,
-    tree_node::{BlockExpression, DeviceDeclarationExpression, Expression, FunctionExpression},
+    tree_node::{
+        BlockExpression, DeviceDeclarationExpression, Expression, FunctionExpression,
+        InvocationExpression, Literal,
+    },
 };
 use quick_error::quick_error;
 use std::{
@@ -9,6 +12,16 @@ use std::{
     io::{BufWriter, Write},
 };
 
+macro_rules! debug {
+    ($self: expr, $debug_value: expr) => {
+        if $self.config.debug {
+            format!($debug_value)
+        } else {
+            "".into()
+        }
+    };
+}
+
 quick_error! {
     #[derive(Debug)]
     pub enum Error {
@@ -22,10 +35,16 @@ quick_error! {
             from()
         }
         DuplicateFunction(func_name: String) {
-            display("{func_name} has already been defined")
+            display("`{func_name}` has already been defined")
+        }
+        UnknownIdentifier(ident: String) {
+            display("`{ident}` is not found in the current scope.")
         }
         InvalidDevice(device: String) {
-            display("{device} is not valid")
+            display("`{device}` is not valid")
+        }
+        AgrumentMismatch(func_name: String) {
+            display("Incorrect number of arguments passed into `{func_name}`")
         }
         Unknown(reason: String) {
             display("{reason}")
@@ -41,6 +60,7 @@ pub struct CompilerConfig {
 pub struct Compiler<'a, W: std::io::Write> {
     parser: ASTParser,
     function_locations: HashMap<String, usize>,
+    function_metadata: HashMap<String, Vec<String>>,
     devices: HashMap<String, String>,
     output: &'a mut BufWriter<W>,
     current_line: usize,
@@ -57,6 +77,7 @@ impl<'a, W: std::io::Write> Compiler<'a, W> {
         Self {
             parser,
             function_locations: HashMap::new(),
+            function_metadata: HashMap::new(),
             devices: HashMap::new(),
             output: writer,
             current_line: 1,
@@ -93,6 +114,9 @@ impl<'a, W: std::io::Write> Compiler<'a, W> {
             Expression::Declaration(var_name, expr) => {
                 self.expression_declaration(var_name, *expr, scope)?
             }
+            Expression::Invocation(expr_invoke) => {
+                self.expression_function_invocation(expr_invoke, scope)?
+            }
             _ => todo!(),
         };
 
@@ -105,16 +129,135 @@ impl<'a, W: std::io::Write> Compiler<'a, W> {
         expr: Expression,
         scope: &mut VariableScope<'v>,
     ) -> Result<(), Error> {
-        scope.add_variable(var_name.clone(), LocationRequest::Persist)?;
-
         match expr {
-            _ => unimplemented!(),
+            Expression::Literal(Literal::Number(num)) => {
+                let var_location =
+                    scope.add_variable(var_name.clone(), LocationRequest::Persist)?;
+                let num_str = num.to_string();
+
+                if let VariableLocation::Temporary(reg) | VariableLocation::Persistant(reg) =
+                    var_location
+                {
+                    self.write_output(format!(
+                        "move r{reg} {num_str} {}",
+                        debug!(self, "#{var_name}")
+                    ))?;
+                } else {
+                    self.write_output(format!("push {num_str} {}", debug!(self, "#{var_name}")))?;
+                }
+            }
+            Expression::Invocation(invoke_expr) => {
+                self.expression_function_invocation(invoke_expr, scope)?;
+
+                // Return value _should_ be in VariableScope::RETURN_REGISTER
+                match scope.add_variable(var_name.clone(), LocationRequest::Persist)? {
+                    VariableLocation::Temporary(reg) | VariableLocation::Persistant(reg) => self
+                        .write_output(format!(
+                            "move r{reg} r{} {}",
+                            VariableScope::RETURN_REGISTER,
+                            debug!(self, "#{var_name}")
+                        ))?,
+                    VariableLocation::Stack(_) => self.write_output(format!(
+                        "push r{} {}",
+                        VariableScope::RETURN_REGISTER,
+                        debug!(self, "#{var_name}")
+                    ))?,
+                }
+            }
+            _ => {
+                return Err(Error::Unknown(
+                    "`{var_name}` declaration of this type is not supported.".into(),
+                ));
+            }
         }
 
         Ok(())
     }
 
-    fn expression_device<'v>(&mut self, expr: DeviceDeclarationExpression) {
+    fn expression_function_invocation(
+        &mut self,
+        invoke_expr: InvocationExpression,
+        stack: &mut VariableScope,
+    ) -> Result<(), Error> {
+        if !self.function_locations.contains_key(&invoke_expr.name) {
+            return Err(Error::UnknownIdentifier(invoke_expr.name));
+        }
+
+        let Some(args) = self.function_metadata.get(&invoke_expr.name) else {
+            return Err(Error::UnknownIdentifier(invoke_expr.name));
+        };
+
+        if args.len() != invoke_expr.arguments.len() {
+            return Err(Error::AgrumentMismatch(invoke_expr.name));
+        }
+
+        // backup all used registers to the stack
+        let active_registers = stack.registers().cloned().collect::<Vec<_>>();
+        for register in &active_registers {
+            stack.add_variable(format!("temp_{register}"), LocationRequest::Stack)?;
+            self.write_output(format!("push r{register}"))?;
+        }
+        for arg in invoke_expr.arguments {
+            match arg {
+                Expression::Literal(Literal::Number(num)) => {
+                    let num_str = num.to_string();
+                    self.write_output(format!("push {num_str}"))?;
+                }
+                Expression::Variable(var_name) => match stack.get_location_of(var_name)? {
+                    VariableLocation::Persistant(reg) | VariableLocation::Temporary(reg) => {
+                        self.write_output(format!("push r{reg}"))?;
+                    }
+                    VariableLocation::Stack(stack_offset) => {
+                        self.write_output(format!(
+                            "sub r{0} sp {stack_offset}",
+                            VariableScope::TEMP_STACK_REGISTER
+                        ))?;
+                        self.write_output(format!(
+                            "get r{0} db r{0}",
+                            VariableScope::TEMP_STACK_REGISTER
+                        ))?;
+                        self.write_output(format!(
+                            "push r{0}",
+                            VariableScope::TEMP_STACK_REGISTER
+                        ))?;
+                    }
+                },
+                _ => {
+                    return Err(Error::Unknown(format!(
+                        "Attempted to call `{}` with an unsupported argument",
+                        invoke_expr.name
+                    )));
+                }
+            }
+        }
+
+        // jump to the function and store current line in ra
+        self.write_output(format!("jal {}", invoke_expr.name))?;
+
+        for register in active_registers {
+            let VariableLocation::Stack(stack_offset) =
+                stack.get_location_of(format!("temp_{register}"))?
+            else {
+                return Err(Error::UnknownIdentifier(format!("temp_{register}")));
+            };
+            self.write_output(format!(
+                "sub r{0} sp {stack_offset}",
+                VariableScope::TEMP_STACK_REGISTER
+            ))?;
+            self.write_output(format!(
+                "get r{register} db r{0}",
+                VariableScope::TEMP_STACK_REGISTER
+            ))?;
+        }
+
+        if stack.stack_offset() > 0 {
+            self.write_output(format!("sub sp sp {}", stack.stack_offset()))?;
+        }
+
+        Ok(())
+    }
+
+    fn expression_device(&mut self, expr: DeviceDeclarationExpression) {
         self.devices.insert(expr.name, expr.device);
     }
 
@@ -166,14 +309,17 @@ impl<'a, W: std::io::Write> Compiler<'a, W> {
             return Err(Error::DuplicateFunction(name));
         }
 
-        self.function_locations
-            .insert(name.clone(), self.current_line);
+        self.function_metadata
+            .insert(name.clone(), arguments.clone());
 
         // Declare the function as a line identifier
         self.write_output(format!("{}:", name))?;
 
+        self.function_locations
+            .insert(name.clone(), self.current_line);
+
         // Create a new block scope for the function body
-        let mut block_scope = VariableScope::scoped(&scope);
+        let mut block_scope = VariableScope::scoped(scope);
 
         let mut saved_variables = 0;
 
@@ -189,14 +335,7 @@ impl<'a, W: std::io::Write> Compiler<'a, W> {
 
             match loc {
                 VariableLocation::Persistant(loc) => {
-                    self.write_output(format!(
-                        "pop r{loc} {}",
-                        if self.config.debug {
-                            format!("#{}", var_name)
-                        } else {
-                            "".into()
-                        }
-                    ))?;
+                    self.write_output(format!("pop r{loc} {}", debug!(self, "#{var_name}")))?;
                 }
                 VariableLocation::Stack(_) => {
                     return Err(Error::Unknown(
@@ -234,8 +373,14 @@ impl<'a, W: std::io::Write> Compiler<'a, W> {
             ));
         };
 
-        self.write_output(format!("sub r0 sp {ra_stack_offset}"))?;
-        self.write_output("get ra db r0")?;
+        self.write_output(format!(
+            "sub r{0} sp {ra_stack_offset}",
+            VariableScope::TEMP_STACK_REGISTER
+        ))?;
+        self.write_output(format!(
+            "get ra db r{0}",
+            VariableScope::TEMP_STACK_REGISTER
+        ))?;
 
         if block_scope.stack_offset() > 0 {
             self.write_output(format!("sub sp sp {}", block_scope.stack_offset()))?;
diff --git a/libs/compiler/src/variable_manager.rs b/libs/compiler/src/variable_manager.rs
index d1be261..edf42e4 100644
--- a/libs/compiler/src/variable_manager.rs
+++ b/libs/compiler/src/variable_manager.rs
@@ -6,7 +6,7 @@ use quick_error::quick_error;
 use std::collections::{HashMap, VecDeque};
 
 const TEMP: [u8; 7] = [1, 2, 3, 4, 5, 6, 7];
-const PERSIST: [u8; 8] = [8, 9, 10, 11, 12, 13, 14, 15];
+const PERSIST: [u8; 7] = [8, 9, 10, 11, 12, 13, 14];
 
 quick_error! {
     #[derive(Debug)]
@@ -72,8 +72,26 @@ impl<'a> Default for VariableScope<'a> {
 }
 
 impl<'a> VariableScope<'a> {
-    pub const TEMP_REGISTER_COUNT: u8 = 8;
-    pub const PERSIST_REGISTER_COUNT: u8 = 8;
+    pub const TEMP_REGISTER_COUNT: u8 = 7;
+    pub const PERSIST_REGISTER_COUNT: u8 = 7;
+
+    pub const RETURN_REGISTER: u8 = 15;
+    pub const TEMP_STACK_REGISTER: u8 = 0;
+
+    pub fn registers(&self) -> impl Iterator<Item = &u8> {
+        self.var_lookup_table
+            .values()
+            .filter(|val| {
+                matches!(
+                    val,
+                    VariableLocation::Temporary(_) | VariableLocation::Persistant(_)
+                )
+            })
+            .map(|loc| match loc {
+                VariableLocation::Persistant(reg) | VariableLocation::Temporary(reg) => reg,
+                _ => unreachable!(),
+            })
+    }
 
     pub fn scoped(parent: &'a VariableScope<'a>) -> Self {
         Self {