diff --git a/README.md b/README.md
index 0ed1f4a..27427fc 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@ A very cool language
 * Growing [standard library](https://github.com/antpiasecki/zern/tree/main/src/std)
 * Produces tiny static executables (11KB for `hello.zr`)
 * No libc required!
-* Has the pipe operator
+* Has the pipe operator, dynamic arrays, hashmaps
 
 ## Syntax
 ```rust
diff --git a/src/codegen_x86_64.rs b/src/codegen_x86_64.rs
index 3442f02..1c30b41 100644
--- a/src/codegen_x86_64.rs
+++ b/src/codegen_x86_64.rs
@@ -732,7 +732,6 @@ _builtin_environ:
             Expr::New(struct_name) => {
                 let struct_fields = &self.symbol_table.structs[&struct_name.lexeme];
 
-                // TODO: panic on mem.alloc error
                 let memory_size = struct_fields.len() * 8;
                 emit!(&mut self.output, "    mov rdi, {}", memory_size);
                 emit!(&mut self.output, "    call mem.alloc");
diff --git a/src/std/std.zr b/src/std/std.zr
index 0865455..1dea503 100644
--- a/src/std/std.zr
+++ b/src/std/std.zr
@@ -5,6 +5,7 @@ const ERR_READ_FAILED       = 3
 const ERR_WRITE_FAILED      = 4
 const ERR_ALLOC_FAILED      = 5
 const ERR_CONNECTION_FAILED = 6
+const ERR_KEY_ERROR         = 7
 
 func err.code[] : i64
     return mem.read64(_builtin_err_code())
@@ -846,6 +847,89 @@ func array.concat[a: Array, b: Array] : Array
         array.set(new_array, a->size + i, array.nth(b, i))
     return new_array
 
+const HashMap._TABLE_SIZE = 100
+
+struct HashMap
+    table: Array
+
+struct HashMap._Node
+    key: str
+    value: any
+    next: HashMap._Node
+
+func HashMap.new[] : HashMap
+    let map: HashMap = new HashMap
+    map->table = array.new_preallocated_and_zeroed(HashMap._TABLE_SIZE)
+    return map
+
+func HashMap.insert[map: HashMap, key: str, value: any] : void
+    let index: i64 = HashMap._djb2(key)
+    let current: HashMap._Node = array.nth(map->table, index)
+
+    while current as ptr
+        if str.equal(current->key, key)
+            current->value = value
+            return 0
+        current = current->next
+
+    let new_node: HashMap._Node = new HashMap._Node
+    new_node->key = str.make_copy(key)
+    new_node->value = value
+    new_node->next = array.nth(map->table, index)
+    array.set(map->table, index, new_node)
+
+func HashMap.get?[map: HashMap, key: str] : any
+    err.clear()
+    let index: i64 = HashMap._djb2(key)
+    let current: HashMap._Node = array.nth(map->table, index)
+
+    while current as ptr
+        if str.equal(current->key, key)
+            return current->value
+        current = current->next
+    
+    err.set(ERR_KEY_ERROR, "key not found")
+    return 0
+
+func HashMap.delete[map: HashMap, key: str] : void
+    let index: i64 = HashMap._djb2(key)
+    let current: HashMap._Node = array.nth(map->table, index)
+    let prev: HashMap._Node = 0 as HashMap._Node
+
+    while current as ptr
+        if str.equal(current->key, key)
+            if prev as ptr
+                prev->next = current->next
+            else
+                array.set(map->table, index, current->next)
+            
+            mem.free(current->key)
+            mem.free(current)
+            return 0
+
+        prev = current
+        current = current->next
+
+func HashMap._djb2[key: str] : i64
+    let hash: i64 = 5381 
+    let key_len: i64 = str.len(key)
+    for i in 0..key_len
+        hash = ((hash << 5) + hash) + key[i]
+    hash = (hash & 0x7fffffffffffffff) // prevent negative
+    return hash % HashMap._TABLE_SIZE
+
+func HashMap.free[map: HashMap] : void
+    for i in 0..HashMap._TABLE_SIZE
+        let current: HashMap._Node = array.nth(map->table, i)
+        while current as ptr
+            let tmp: HashMap._Node = current
+            current = current->next
+            mem.free(tmp->key)
+            mem.free(tmp)
+
+    array.free(map->table)
+    mem.free(map)
+
 func alg.quicksort[arr: Array] : void
     alg._do_quicksort(arr, 0, arr->size - 1)
 
diff --git a/src/symbol_table.rs b/src/symbol_table.rs
index f7ec70b..f38d10b 100644
--- a/src/symbol_table.rs
+++ b/src/symbol_table.rs
@@ -66,10 +66,7 @@ impl SymbolTable {
         match stmt {
             Stmt::Const { name, value } => {
                 if self.is_name_defined(&name.lexeme) {
-                    return error!(
-                        name.loc,
-                        format!("tried to redefine constant '{}'", name.lexeme)
-                    );
+                    return error!(name.loc, format!("tried to redefine '{}'", name.lexeme));
                 }
                 if value.lexeme.starts_with("0x") {
                     self.constants.insert(
diff --git a/src/typechecker.rs b/src/typechecker.rs
index 11d6983..ce9b358 100644
--- a/src/typechecker.rs
+++ b/src/typechecker.rs
@@ -166,8 +166,29 @@ impl<'a> TypeChecker<'a> {
                 body,
                 exported: _,
             } => {
-                if name.lexeme == "main" && return_type.lexeme != "i64" {
-                    return error!(&name.loc, "main must return i64");
+                if name.lexeme == "main" {
+                    if return_type.lexeme != "i64" {
+                        return error!(&name.loc, "main function must return i64");
+                    }
+
+                    if !params.is_empty() && params.len() != 2 {
+                        return error!(&name.loc, "main function must accept 0 or 2 parameters");
+                    }
+
+                    if params.len() == 2 {
+                        if params[0].var_type.lexeme != "i64" {
+                            return error!(
+                                &name.loc,
+                                "first parameter of the main function must be a i64"
+                            );
+                        }
+                        if params[1].var_type.lexeme != "ptr" {
+                            return error!(
+                                &name.loc,
+                                "second parameter of the main function must be a ptr"
+                            );
+                        }
+                    }
                 }
 
                 if !self.is_valid_type_name(&return_type.lexeme) {