diff --git a/CHANGELOG.md b/CHANGELOG.md
index 70b2a5b..41b06fc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,11 @@
 - [ ] Stdlib
 - [ ] Document code
 
+## v0.0.3
+
+- Get datatype of an identifier from the symbol table
+- Improve documentation of the code
+
 ## v0.0.2
 
 - Compilation of `val` and `var` bindings with a number, string or boolean as value.
diff --git a/src/ast_types.rs b/src/ast_types.rs
index c8d65ac..f657079 100644
--- a/src/ast_types.rs
+++ b/src/ast_types.rs
@@ -22,4 +22,5 @@ pub enum Expression<'a> {
     Number(&'a String),
     String(&'a String),
     Boolean(bool),
+    Identifier(&'a String),
 }
diff --git a/src/codegen/binding.rs b/src/codegen/binding.rs
index 5155562..301a643 100644
--- a/src/codegen/binding.rs
+++ b/src/codegen/binding.rs
@@ -2,6 +2,7 @@ use crate::ast_types::Binding;
 use super::Transpilable;
 
 impl Transpilable for Binding<'_> {
+    /// Transpiles val and var bindings into JS.
     fn transpile(&self) -> String {
         match self {
             Binding::Val(val_binding) => {
diff --git a/src/codegen/expression.rs b/src/codegen/expression.rs
index a4ed8ce..183d217 100644
--- a/src/codegen/expression.rs
+++ b/src/codegen/expression.rs
@@ -2,6 +2,13 @@ use crate::ast_types::Expression;
 use super::Transpilable;
 
 impl Transpilable for Expression<'_> {
+    /// Transpiles an Expression to JS
+    ///
+    /// Right now the expressions in the grammar are:
+    /// - Number
+    /// - String
+    /// - Boolean
+    /// - Identifier
     fn transpile(&self) -> String {
         match self {
             Expression::Number(value) => {
@@ -13,6 +20,9 @@ impl Transpilable for Expression<'_> {
             Expression::Boolean(value) => {
                 String::from(if *value {"true"} else {"false"})
             }
+            Expression::Identifier(value) => {
+                String::from(*value)
+            }
         }
     }
 }
@@ -48,4 +58,13 @@ mod tests {
         
         assert_eq!("true", result);
     }
+    
+    #[test]
+    fn should_transpile_identifier() {
+        let s = String::from("newValue");
+        let exp = Expression::Identifier(&s);
+        let result = exp.transpile();
+        
+        assert_eq!("newValue", result);
+    }
 }
diff --git a/src/codegen/mod.rs b/src/codegen/mod.rs
index 8108701..48781d8 100644
--- a/src/codegen/mod.rs
+++ b/src/codegen/mod.rs
@@ -4,11 +4,13 @@ mod expression;
 mod binding;
 mod module_ast;
 
+/// Trait that the AST and its nodes implement to support transformation to JavaScript
 trait Transpilable {
+    /// Transforms this struct into JavaScript
     fn transpile(&self) -> String;
 }
 
-/// Generates JavaScript from the AST
+/// Transforms an AST to its representation in JavaScript
 pub fn codegen<'a>(ast: &'a ModuleAST) -> String {
     ast.transpile()
 }
diff --git a/src/codegen/module_ast.rs b/src/codegen/module_ast.rs
index 24c34f9..e9f17b4 100644
--- a/src/codegen/module_ast.rs
+++ b/src/codegen/module_ast.rs
@@ -2,6 +2,8 @@ use crate::ast_types::ModuleAST;
 use super::Transpilable;
 
 impl Transpilable for ModuleAST<'_> {
+    /// Transpiles the whole AST into JS, using this same trait on the
+    /// nodes and leaves of the AST
     fn transpile(&self) -> String {
         let bindings_str: Vec::<String> = self.bindings.iter().map(|binding| binding.transpile()).collect();
 
diff --git a/src/lexic/lex_error.rs b/src/lexic/lex_error.rs
index 3e43059..cc4c65a 100755
--- a/src/lexic/lex_error.rs
+++ b/src/lexic/lex_error.rs
@@ -1,6 +1,9 @@
 
+/// Represents an error in the scanning process
 #[derive(Debug)]
 pub struct LexError {
+    /// Position where the offending char was found
     pub position: usize,
+    /// Reason of the errror
     pub reason: String,
 }
diff --git a/src/lexic/mod.rs b/src/lexic/mod.rs
index 102a571..2894eef 100755
--- a/src/lexic/mod.rs
+++ b/src/lexic/mod.rs
@@ -6,11 +6,29 @@ use lex_error::LexError;
 
 type Chars = Vec<char>;
 
+/// Represents the result of scanning a single token from the input
 pub enum LexResult {
-    // A token was scanned
+    /// A token was found. The first element is the token, and the
+    /// second element is the position in the input after the token.
+    ///
+    /// E.g., given an input 
+    ///
+    /// "`identifier 55`"
+    ///
+    /// scanning from a position `0`, the result would be
+    ///
+    /// `Some(Token("identifier"), 10)`.
+    ///
+    /// where:
+    /// - `Token("identifier")` is the token
+    /// - `10` is the position where the token ends, and from where the next token
+    /// should be scanned
     Some(Token, usize),
-    // No token was found, but there was no error (EOF)
+    /// No token was found. This indicates that EOF has been reached.
+    ///
+    /// Contains the last position, which should be the input lenght - 1
     None(usize),
+    /// An error was found while scanning.
     Err(LexError),
 }
 
@@ -38,6 +56,7 @@ pub fn get_tokens(input: &String) -> Result<Vec<Token>, LexError> {
     Ok(results)
 }
 
+/// Scans a single token from `chars`, starting from `current_pos`
 fn next_token(chars: &Chars, current_pos: usize) -> LexResult {
     let next_char = peek(chars, current_pos);
 
@@ -72,11 +91,13 @@ fn next_token(chars: &Chars, current_pos: usize) -> LexResult {
         })
 }
 
+/// Returns the char at `pos`
 fn peek(input: &Chars, pos: usize) -> char {
     let result = input.get(pos).unwrap_or(&'\0');
     *result
 }
 
+/// Whether there is still input based on `current_pos`
 fn has_input(input: &Chars, current_pos: usize) -> bool {
     current_pos < input.len()
 }
diff --git a/src/lexic/scanner/identifier.rs b/src/lexic/scanner/identifier.rs
index b8c58f1..d9ecef0 100755
--- a/src/lexic/scanner/identifier.rs
+++ b/src/lexic/scanner/identifier.rs
@@ -9,12 +9,15 @@ fn str_is_keyword(s: &String) -> Option<TokenType> {
     }
 }
 
-
+/// Scans an identifier. This function assumes that `start_pos` is the start of
+/// a valid identifier
 pub fn scan(start_char: char, chars: &Vec<char>, start_pos: usize) -> LexResult {
+    // The scanning is done by this recursive function
     scan_impl(chars, start_pos + 1, format!("{}", start_char))
 }
 
-pub fn scan_impl(chars: &Vec<char>, start_pos: usize, current: String) -> LexResult {
+/// Recursive funtion that scans the identifier
+fn scan_impl(chars: &Vec<char>, start_pos: usize, current: String) -> LexResult {
     match chars.get(start_pos) {
         Some(c) if utils::is_identifier_char(*c) => {
             scan_impl(chars, start_pos + 1, utils::str_append(current, *c))
diff --git a/src/lexic/scanner/mod.rs b/src/lexic/scanner/mod.rs
index 43ba880..74517d1 100755
--- a/src/lexic/scanner/mod.rs
+++ b/src/lexic/scanner/mod.rs
@@ -5,19 +5,22 @@ mod operator;
 mod identifier;
 mod string;
 
-/// Attempts to scan a number. Returns None to be able to chain other scanner
+
+// This module contains the individual scanners, and exports them
+
+/// Attempts to scan a number. If not found returns None to be able to chain other scanner
 pub fn number(c: char, chars: &Vec<char>, start_pos: usize) -> Option<LexResult> {
     utils::is_digit(c).then(|| number::scan(chars, start_pos))
 }
 
 
-/// Attempts to scan an operator. Returns None to be able to chain other scanner
+/// Attempts to scan an operator. If not found returns None to be able to chain other scanner
 pub fn operator(c: char, chars: &Vec<char>, start_pos: usize) -> Option<LexResult> {
     utils::is_operator(c).then(|| operator::scan(chars, start_pos))
 }
 
 
-/// Attempts to scan a grouping sign. Returns None to be able to chain other scanner
+/// Attempts to scan a grouping sign. If not found returns None to be able to chain other scanner
 pub fn grouping_sign(c: char, _: &Vec<char>, start_pos: usize) -> Option<LexResult> {
     let token_type = match c {
         '(' => TokenType::LeftParen,
@@ -38,13 +41,14 @@ pub fn grouping_sign(c: char, _: &Vec<char>, start_pos: usize) -> Option<LexResu
 }
 
 
-/// Attempts to scan an identifier. Returns None to be able to chain other scanner
+/// Attempts to scan an identifier. If not found returns None to be able to chain other scanner
 pub fn identifier(c: char, chars: &Vec<char>, start_pos: usize) -> Option<LexResult> {
     (utils::is_lowercase(c) || c == '_')
         .then(|| identifier::scan(c, chars, start_pos))
 }
 
 
+/// Attempts to scan a string. If not found returns None to be able to chain other scanner
 pub fn string(c: char, chars: &Vec<char>, start_pos: usize) -> Option<LexResult> {
     (c == '"').then(|| string::scan(chars, start_pos + 1))
 }
diff --git a/src/lexic/scanner/string.rs b/src/lexic/scanner/string.rs
index ec1b764..db2c77e 100755
--- a/src/lexic/scanner/string.rs
+++ b/src/lexic/scanner/string.rs
@@ -11,6 +11,7 @@ pub fn scan(chars: &Vec<char>, start_pos: usize) -> LexResult {
     scan_impl(chars, start_pos, String::from(""))
 }
 
+/// Recursive function that does the scanning
 pub fn scan_impl(chars: &Vec<char>, start_pos: usize, current: String) -> LexResult {
     match chars.get(start_pos) {
         Some(c) if *c == '"' => {
@@ -56,6 +57,7 @@ pub fn scan_impl(chars: &Vec<char>, start_pos: usize, current: String) -> LexRes
 }
 
 
+/// Checks if the char at `start_pos` is a escape character
 fn test_escape_char(chars: &Vec<char>, start_pos: usize) -> Option<char> {
     if let Some(c) = chars.get(start_pos) {
         match *c {
diff --git a/src/lexic/utils.rs b/src/lexic/utils.rs
index eea48f2..dd012f2 100755
--- a/src/lexic/utils.rs
+++ b/src/lexic/utils.rs
@@ -1,16 +1,19 @@
-
+/// Whether `c` is between `0-9`
 pub fn is_digit(c: char) -> bool {
     '0' <= c && c <= '9'
 }
 
+/// Whether `c` is between `a-fA-F`
 pub fn is_hex_digit(c: char) -> bool {
     is_digit(c) || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F'
 }
 
+/// Joins a String and a char
 pub fn str_append(current: String, c: char) -> String {
     format!("{}{}", current, c)
 }
 
+/// Whether `c` is an operator char.
 pub fn is_operator(c: char) -> bool {
     c == '+' || c == '-' || c == '=' || c == '*' || c == '!'
              || c == '\\' || c == '/' || c == '|' || c == '@'
@@ -19,14 +22,17 @@ pub fn is_operator(c: char) -> bool {
              || c == '^' || c == '.' || c == ':'
 }
 
+/// Whether `c` is between `a-z`
 pub fn is_lowercase(c: char) -> bool {
     c >= 'a' && c <= 'z'
 }
 
+/// Whether `c` is between `A-Z`
 pub fn is_uppercase(c: char) -> bool {
     c >= 'A' && c <= 'Z'
 }
 
+/// Whether `c` is between `a-zA-Z_0-9`
 pub fn is_identifier_char(c: char) -> bool {
     is_lowercase(c) || is_uppercase(c) || c == '_' || is_digit(c)
 }
diff --git a/src/repl/mod.rs b/src/repl/mod.rs
index fa79cfb..616224f 100755
--- a/src/repl/mod.rs
+++ b/src/repl/mod.rs
@@ -8,6 +8,7 @@ use super::syntax;
 use super::semantic;
 use super::codegen;
 
+/// Executes Lexical analysis, handles errors and calls build_ast for the next phase
 fn compile(input: &String) {
     let _tokens = lexic::get_tokens(input);
 
@@ -22,6 +23,9 @@ fn compile(input: &String) {
 
 }
 
+/// Executes Syntax analysis, and for now, Semantic analysis and Code generation.
+///
+/// Prints the generated code in stdin
 fn build_ast(tokens: Vec<Token>) {
     let ast = syntax::construct_ast(&tokens);
 
@@ -38,6 +42,7 @@ fn build_ast(tokens: Vec<Token>) {
     }
 }
 
+/// Executes the REPL, reading from stdin, compiling and emitting JS to stdout
 pub fn run() -> io::Result<()> {
     let stdin = io::stdin();
     let mut buffer = String::new();
diff --git a/src/semantic/mod.rs b/src/semantic/mod.rs
index 7557eca..539736e 100644
--- a/src/semantic/mod.rs
+++ b/src/semantic/mod.rs
@@ -8,24 +8,35 @@ pub fn check_ast<'a>(ast: &'a mut ModuleAST, symbol_table: &'a mut SymbolTable)
             Binding::Val(binding) => {
                 symbol_table.add(
                     binding.identifier,
-                    get_expression_type(&binding.expression).as_str()
+                    get_expression_type(&binding.expression, symbol_table).as_str()
                 );
             }
             Binding::Var(binding) => {
                 symbol_table.add(
                     binding.identifier,
-                    get_expression_type(&binding.expression).as_str(),
+                    get_expression_type(&binding.expression, symbol_table).as_str(),
                 );
             }
         }
     }
 }
 
-fn get_expression_type(exp: &Expression) -> String {
+fn get_expression_type(exp: &Expression, symbol_table: &SymbolTable) -> String {
     match exp {
         Expression::Number(_) => String::from(_NUMBER),
         Expression::String(_) => String::from(_STRING),
         Expression::Boolean(_) => String::from(_BOOLEAN),
+        Expression::Identifier(id) => {
+            match symbol_table.get_type(*id) {
+                Some(datatype) => {
+                    datatype
+                }
+                None => {
+                    // Should add an error to the list instead of panicking
+                    panic!("Semantic analysis: identifier {} not found", id);
+                }
+            }
+        }
     }
 }
 
@@ -71,4 +82,24 @@ mod tests {
         assert!(test_type(String::from("val a = false"), _BOOLEAN));
         assert!(test_type(String::from("var a = true"), _BOOLEAN));
     }
+    
+    #[test]
+    fn should_get_type_from_identifier() {
+        let mut table = SymbolTable::new();
+        let tokens = lexic::get_tokens(&String::from("val identifier = 20")).unwrap();
+        let mut ast = syntax::construct_ast(&tokens).unwrap();
+
+        // Add an identifier
+        check_ast(&mut ast, &mut table);
+        
+        let tokens = lexic::get_tokens(&String::from("val newValue = identifier")).unwrap();
+        let mut ast = syntax::construct_ast(&tokens).unwrap();
+        
+        // Add a new value that references an identifier
+        check_ast(&mut ast, &mut table);
+        
+        // The type should be Num
+        let current_type = table.get_type("newValue").unwrap();
+        assert_eq!(_NUMBER, current_type);
+    }
 }
diff --git a/src/symbol_table.rs b/src/symbol_table.rs
index 3b7e716..9b9fd39 100644
--- a/src/symbol_table.rs
+++ b/src/symbol_table.rs
@@ -39,6 +39,14 @@ impl SymbolTable {
             })
             .unwrap_or(false)
     }
+    
+    pub fn get_type(&self, identifier: &str) -> Option<String> {
+        self.table
+            .get_key_value(&String::from(identifier))
+            .and_then(|(_, value)| {
+                Some(String::from(value))
+            })
+    }
 }
 
 
diff --git a/src/syntax/expression.rs b/src/syntax/expression.rs
index c4cd3b7..ea278cb 100644
--- a/src/syntax/expression.rs
+++ b/src/syntax/expression.rs
@@ -1,7 +1,12 @@
 use crate::token::{Token, TokenType};
 use super::ast_types::Expression;
 
-
+/// An expression can be:
+///
+/// - A number
+/// - A string
+/// - A boolean
+/// - An identifier
 pub fn try_parse(tokens: &Vec<Token>, pos: usize) -> Option<Expression> {
     tokens
         .get(pos)
@@ -16,6 +21,9 @@ pub fn try_parse(tokens: &Vec<Token>, pos: usize) -> Option<Expression> {
                 TokenType::Identifier if token.value == "true" || token.value == "false" => {
                     Some(Expression::Boolean(token.value == "true"))
                 }
+                TokenType::Identifier => {
+                    Some(Expression::Identifier(&token.value))
+                }
                 _ => None
             }
         })
@@ -48,4 +56,26 @@ mod tests {
             _ => panic!() 
         }
     }
+    
+    #[test]
+    fn should_parse_a_boolean() {
+        let tokens = get_tokens(&String::from("true")).unwrap();
+        let expression = try_parse(&tokens, 0).unwrap();
+
+        match expression {
+            Expression::Boolean(value) => assert!(value),
+            _ => panic!() 
+        }
+    }
+    
+    #[test]
+    fn should_parse_an_identifier() {
+        let tokens = get_tokens(&String::from("someIdentifier")).unwrap();
+        let expression = try_parse(&tokens, 0).unwrap();
+
+        match expression {
+            Expression::Identifier(value) => assert_eq!("someIdentifier", value),
+            _ => panic!() 
+        }
+    }
 }