Struct hack_asm::SymbolTable

pub struct SymbolTable { /* private fields */ }

The symbol table stores and resolves symbols (labels and variables) to their associated addresses or values.

List of predefined symbols

Virtual Registers

Symbol	Value
R0	0
R1	1
…	…
R15	15

---

Input/Output

Symbol	Value
SCREEN	16384
KBD	24576

---

Reserved

Symbol	Value
SP	0
LCL	1
ARG	2
THIS	3
That	4

---

Example

Basic Usage

let mut table = SymbolTable::new();
table.set("value", 42).unwrap();
assert!(table.set("value", 101).is_err());      // a symbols' value may only be set once

assert_eq!(table.get("value").unwrap(), 42);    // defined symbol
assert!(table.get("undefined").is_err());    // undefined symbol
assert!(table.get("VALUE").is_err());       // undefined because the table is case sensitive

Predefined Symbols

By design of the Hack assembly language we already have predefined symbols inside of our symbol table.

let mut table = SymbolTable::new();

assert!(table.set("R10", 101).is_err());             // built in symbol cannot be redefined
assert_eq!(table.get("SCREEN").unwrap(), 16384);   // predefined
assert_eq!(table.get("R10").unwrap(), 10);         // predefined

Implementations

impl SymbolTable

pub fn new() -> Self

pub fn set(
    &mut self,
    name: &str,
    value: HackInt
) -> Result<(), SymbolTableError>

Sets the value of a symbol to the specified value. This function should also create the symbol if it does not exist. Overwriting a built in or an already defined symbol is not allowed. May return a SymbolTableError

Arguments

• name - A string that contains the name of the symbol
• value - The value (or address) associated with the symbol

pub fn get(&self, name: &str) -> Result<HackInt, SymbolTableError>

Retrieves the value of a symbol. May return a SymbolTableError

Arguments

• name - The symbol name to look up

Trait Implementations

impl Default for SymbolTable

fn default() -> Self

Returns the “default value” for a type.