diff --git a/src/repl/mod.rs b/src/repl/mod.rs
index 9d8bb74..a943d96 100755
--- a/src/repl/mod.rs
+++ b/src/repl/mod.rs
@@ -13,7 +13,7 @@ fn compile(input: &String) {
         Ok(tokens) => {
             let mut ast = syntax::construct_ast(&tokens).unwrap();
             let mut table = SymbolTable::new();
-            let new_ast = semantic::check_ast(&mut ast, &mut table);
+            semantic::check_ast(&mut ast, &mut table);
         },
         Err(error) => {
             eprintln!("Error scanning.\n{} at pos {}", error.reason, error.position)
diff --git a/src/semantic/mod.rs b/src/semantic/mod.rs
index f240336..2437f0f 100644
--- a/src/semantic/mod.rs
+++ b/src/semantic/mod.rs
@@ -1,14 +1,23 @@
-use crate::symbol_table;
+use super::symbol_table::{SymbolTable, _NUMBER};
+use super::ast_types::{ModuleAST, Binding};
 
-use super::symbol_table::SymbolTable;
-use super::ast_types::ModuleAST;
-
-pub fn check_ast<'a>(ast: &'a mut ModuleAST, symbol_table: &'a mut SymbolTable) -> Option<ModuleAST<'a>> {
-    None
+/// Checks the ast. In the future should return a list of errors.
+pub fn check_ast<'a>(ast: &'a mut ModuleAST, symbol_table: &'a mut SymbolTable) {
+    for binding in &ast.bindings {
+        match binding {
+            Binding::Val(val_binding) => {
+                // TODO: create a function to get the datatype, instead of a hardcoded value
+                symbol_table.add(val_binding.identifier, _NUMBER);
+            }
+        }
+    }
 }
 
 #[cfg(test)]
 mod tests {
+    use crate::syntax;
+    use crate::lexic;
+
     use super::*;
 
     /*
@@ -31,4 +40,16 @@ mod tests {
         identifier: Num
     }
      */
+
+    #[test]
+    fn should_update_symbol_table() {
+        let tokens = lexic::get_tokens(&String::from("val identifier = 20")).unwrap();
+        let mut table = SymbolTable::new();
+        let mut ast = syntax::construct_ast(&tokens).unwrap();
+
+        check_ast(&mut ast, &mut table);
+
+        let result = table.test("identifier");
+        assert_eq!(true, result);
+    }
 }
diff --git a/src/symbol_table.rs b/src/symbol_table.rs
index 2e53bd3..3b7e716 100644
--- a/src/symbol_table.rs
+++ b/src/symbol_table.rs
@@ -11,7 +11,7 @@ pub struct SymbolTable {
 
 impl SymbolTable {
     pub fn new() -> SymbolTable {
-        let mut symbol_table = HashMap::<String, String>::new();
+        let symbol_table = HashMap::<String, String>::new();
 
         SymbolTable {
             table: symbol_table,
@@ -25,6 +25,20 @@ impl SymbolTable {
     pub fn test(&self, identifier: &str) -> bool {
         return self.table.contains_key::<String>(&String::from(identifier));
     }
+
+    pub fn check_type(&self, identifier: &str, datatype: &str) -> bool {
+        self.table
+            .get_key_value(&String::from(identifier))
+            .and_then(|(_, value)| {
+                if value == &String::from(datatype) {
+                    Some(true)
+                }
+                else {
+                    Some(false)
+                }
+            })
+            .unwrap_or(false)
+    }
 }
 
 
@@ -43,4 +57,12 @@ mod tests {
         table.add("identifier", _NUMBER);
         assert_eq!(true, table.test("identifier"))
     }
+
+    #[test]
+    fn should_check_type() {
+        let mut table = SymbolTable::new();
+        table.add("firstNumber", _NUMBER);
+        
+        assert!(table.check_type("firstNumber", _NUMBER));
+    }
 }