diff --git a/examples/acme_parser.rs b/examples/acme_parser.rs
deleted file mode 100644
index a69cc6e0..00000000
--- a/examples/acme_parser.rs
+++ /dev/null
@@ -1,115 +0,0 @@
-use std::sync::{Arc, Mutex};
-
-extern crate datafusion_sql;
-
-use datafusion_sql::ansi::tokenizer::ANSISQLTokenizer;
-use datafusion_sql::ansi::parser::ANSISQLParser;
-use datafusion_sql::tokenizer::*;
-use datafusion_sql::parser::*;
-
-/// This example demonstrates building a custom ACME parser that extends the generic parser
-/// by adding support for a factorial expression `!! expr`.
-
-/// Custom SQLToken
-#[derive(Debug,PartialEq)]
-enum AcmeToken {
-    /// Factorial token `!!`
-    Factorial
-}
-
-/// Custom SQLExpr
-#[derive(Debug)]
-enum AcmeExpr {
-    /// Factorial expression
-    Factorial(Box<SQLExpr<AcmeExpr>>)
-}
-
-struct AcmeTokenizer {
-    ansi_tokenizer: Arc<Mutex<SQLTokenizer<AcmeToken>>>
-}
-
-/// The ACME tokenizer looks for the factorial operator `!!` but delegates everything else
-impl SQLTokenizer<AcmeToken> for AcmeTokenizer {
-
-    fn precedence(&self, _token: &SQLToken<AcmeToken>) -> usize {
-        unimplemented!()
-    }
-
-    fn next_token(&mut self, chars: &mut CharSeq) -> Result<Option<SQLToken<AcmeToken>>, TokenizerError> {
-        let mut ansi = self.ansi_tokenizer.lock().unwrap();
-        match chars.peek() {
-            Some(&ch) => match ch {
-                '!' => {
-                    chars.mark();
-                    chars.next(); // consume the first `!`
-                    match chars.peek() {
-                        Some(&ch) => match ch {
-                            '!' => {
-                                chars.next(); // consume the second `!`
-                                Ok(Some(SQLToken::Custom(AcmeToken::Factorial)))
-                            },
-                            _ => {
-                                chars.reset();
-                                ansi.next_token(chars)
-                            }
-                        },
-                        None => {
-                            chars.reset();
-                            ansi.next_token(chars)
-                        }
-                    }
-                }
-                _ => ansi.next_token(chars)
-            }
-            _ => ansi.next_token(chars)
-        }
-    }
-
-}
-
-struct AcmeParser {
-    tokenizer: Arc<Mutex<SQLTokenizer<AcmeToken>>>
-}
-
-impl AcmeParser {
-
-    pub fn new(tokenizer: Arc<Mutex<SQLTokenizer<AcmeToken>>>) -> Self {
-        AcmeParser { tokenizer: tokenizer.clone() }
-    }
-
-}
-impl SQLParser<AcmeToken, AcmeExpr> for AcmeParser {
-
-    fn parse_prefix(&mut self, chars: &mut CharSeq) -> Result<Option<Box<SQLExpr<AcmeExpr>>>, ParserError<AcmeToken>> {
-        Ok(None)
-    }
-
-    fn parse_infix(&mut self, chars: &mut CharSeq, left: &SQLExpr<AcmeExpr>, precedence: usize) -> Result<Option<Box<SQLExpr<AcmeExpr>>>, ParserError<AcmeToken>> {
-        Ok(None)
-    }
-}
-
-fn main() {
-
-    let sql = "1 + !! 5 * 2";
-
-    // ANSI SQL tokenizer
-    let ansi_tokenizer = Arc::new(Mutex::new(ANSISQLTokenizer { }));
-
-    // Custom ACME tokenizer
-    let mut acme_tokenizer = Arc::new(Mutex::new(AcmeTokenizer {
-        ansi_tokenizer: ansi_tokenizer.clone()
-    }));
-
-    // Create parsers
-    let ansi_parser = Arc::new(Mutex::new(ANSISQLParser::new(acme_tokenizer.clone())));
-    let acme_parser = Arc::new(Mutex::new(AcmeParser::new(acme_tokenizer.clone())));
-
-    let mut pratt_parser = PrattParser {
-        chars: CharSeq::new(sql),
-        parsers: vec![acme_parser, ansi_parser]
-    };
-
-    let expr = pratt_parser.parse_expr().unwrap();
-    println!("{:?}", expr);
-}
diff --git a/examples/parse_sql.rs b/examples/parse_sql.rs
new file mode 100644
index 00000000..b1b85e72
--- /dev/null
+++ b/examples/parse_sql.rs
@@ -0,0 +1,20 @@
+use std::sync::{Arc, Mutex};
+
+extern crate datafusion_sql;
+
+use datafusion_sql::ansi::tokenizer::ANSISQLTokenizer;
+use datafusion_sql::ansi::parser::ANSISQLParser;
+use datafusion_sql::tokenizer::*;
+use datafusion_sql::parser::*;
+
+
+fn main() {
+
+    let sql = "SELECT 1 + 1";
+
+    // Create parsers
+    match ANSISQLParser::parse(sql).unwrap() {
+        Some(ast) => println!("{:?}", ast),
+        _ => {}
+    }
+}
diff --git a/src/ansi/parser.rs b/src/ansi/parser.rs
index 5af62feb..f0259c31 100644
--- a/src/ansi/parser.rs
+++ b/src/ansi/parser.rs
@@ -1,30 +1,56 @@
 use std::cmp::PartialEq;
 use std::fmt::Debug;
-//use std::iter::Peekable;
-//use std::str::Chars;
-
-use std::sync::{Arc, Mutex};
+//use std::rc::Rc;
+//use std::sync::{Arc, Mutex};
 
+use super::tokenizer::ANSISQLTokenizer;
 use super::super::tokenizer::*;
 use super::super::parser::*;
 
-pub struct ANSISQLParser<TokenType> {
-    tokenizer: Arc<Mutex<SQLTokenizer<TokenType>>>
+pub struct ANSISQLParser {
+    tokenizer: Box<SQLTokenizer>
 }
 
-impl<TokenType> ANSISQLParser<TokenType> where TokenType: Debug + PartialEq {
+impl ANSISQLParser where {
 
-    pub fn new(tokenizer: Arc<Mutex<SQLTokenizer<TokenType>>>) -> Self {
-        ANSISQLParser { tokenizer: tokenizer.clone() }
+    pub fn parse(sql: &str) -> Result<Option<Box<SQLExpr>>, ParserError> {
+        let mut parser = ANSISQLParser { tokenizer: Box::new(ANSISQLTokenizer::new(sql)) };
+        parser.parse_expr()
     }
 }
 
-impl<TokenType, ExprType> SQLParser<TokenType, ExprType> for ANSISQLParser<TokenType>
-    where TokenType: Debug + PartialEq, ExprType: Debug {
+impl SQLParser for ANSISQLParser {
 
-    fn parse_prefix(&mut self, chars: &mut CharSeq) -> Result<Option<Box<SQLExpr<ExprType>>>, ParserError<TokenType>> {
+    fn parse_expr(&mut self) -> Result<Option<Box<SQLExpr>>, ParserError> {
 
-        match self.tokenizer.lock().unwrap().next_token(chars)? {
+        let precedence: usize = 0;
+
+        let mut e = self.parse_prefix()?;
+
+        match e {
+            Some(mut expr) => {
+                while let Some(token) = self.tokenizer.peek_token()? {
+                    let next_precedence = self.tokenizer.precedence(&token);
+
+                    if precedence >= next_precedence {
+                        break;
+                    }
+
+                    expr = self.parse_infix(&expr, next_precedence)?.unwrap(); //TODO: fix me
+                }
+
+                Ok(Some(expr))
+            }
+            _ => {
+                Ok(None)
+            }
+        }
+
+    }
+
+    fn parse_prefix(&mut self) -> Result<Option<Box<SQLExpr>>, ParserError> {
+
+        match self.tokenizer.next_token()? {
             Some(SQLToken::Keyword(ref k)) => match k.to_uppercase().as_ref() {
                 "INSERT" => unimplemented!(),
                 "UPDATE" => unimplemented!(),
@@ -37,7 +63,7 @@ impl<TokenType, ExprType> SQLParser<TokenType, ExprType> for ANSISQLParser<Token
         }
     }
 
-    fn parse_infix(&mut self, _chars: &mut CharSeq, _left: &SQLExpr<ExprType>, _precedence: usize) -> Result<Option<Box<SQLExpr<ExprType>>>, ParserError<TokenType>> {
+    fn parse_infix(&mut self, _left: &SQLExpr, _precedence: usize) -> Result<Option<Box<SQLExpr>>, ParserError> {
         unimplemented!()
     }
 }
diff --git a/src/ansi/tokenizer.rs b/src/ansi/tokenizer.rs
index f34965f3..9714559f 100644
--- a/src/ansi/tokenizer.rs
+++ b/src/ansi/tokenizer.rs
@@ -4,26 +4,37 @@ use std::fmt::Debug;
 use super::super::tokenizer::*;
 
 pub struct ANSISQLTokenizer {
+    chars: CharSeq
 }
 
-impl<TokenType> SQLTokenizer<TokenType> for ANSISQLTokenizer
-    where TokenType: Debug + PartialEq {
+impl ANSISQLTokenizer {
+    pub fn new(sql: &str) -> Self {
+        ANSISQLTokenizer { chars: CharSeq::new(sql) }
+    }
+}
 
-    fn precedence(&self, _token: &SQLToken<TokenType>) -> usize {
+impl SQLTokenizer for ANSISQLTokenizer {
+
+    fn precedence(&self, _token: &SQLToken) -> usize {
         unimplemented!()
     }
 
-    fn next_token(&mut self, chars: &mut CharSeq) -> Result<Option<SQLToken<TokenType>>, TokenizerError> {
-        match chars.next() {
+    fn peek_token(&mut self) -> Result<Option<SQLToken>, TokenizerError> {
+        unimplemented!()
+    }
+
+
+    fn next_token(&mut self) -> Result<Option<SQLToken>, TokenizerError> {
+        match self.chars.next() {
             Some(ch) => match ch {
                 ' ' | '\t' | '\n' => Ok(Some(SQLToken::Whitespace(ch))),
                 '0' ... '9' => {
                     let mut s = String::new();
                     s.push(ch);
-                    while let Some(&ch) = chars.peek() {
+                    while let Some(&ch) = self.chars.peek() {
                         match ch {
                             '0' ... '9' => {
-                                chars.next(); // consume
+                                self.chars.next(); // consume
                                 s.push(ch);
                             },
                             _ => break
diff --git a/src/parser.rs b/src/parser.rs
index d514692a..afbfda1d 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -1,6 +1,5 @@
 use std::cmp::PartialEq;
 use std::fmt::Debug;
-use std::sync::{Arc, Mutex};
 
 use super::tokenizer::*;
 
@@ -8,7 +7,7 @@ use super::tokenizer::*;
 
 /// ANSI SQL:2011 Data Types
 #[derive(Debug)]
-pub enum SQLDataType<T> {
+pub enum SQLDataType {
     /// BOOLEAN
     Boolean,
     /// NUMERIC, DECIMAL, DEC
@@ -49,14 +48,12 @@ pub enum SQLDataType<T> {
     Time { precision: usize, tz: bool },
     /// Time: `TIMESTAMP [(precision)] [WITH TIME ZONE | WITHOUT TIME ZONE]`
     Timestamp { precision: usize, tz: bool },
-    /// Custom data type
-    Custom(T)
 }
 
 
 
 #[derive(Debug)]
-pub enum SQLOperator<T> {
+pub enum SQLOperator {
     Plus,
     Minus,
     Mult,
@@ -66,217 +63,44 @@ pub enum SQLOperator<T> {
     GtEq,
     Lt,
     LtEq,
-    Custom(T) // extension point for vendor-specific operators
 }
 
 /// SQL Expressions
 #[derive(Debug)]
-pub enum SQLExpr<ExprType> {
+pub enum SQLExpr{
     /// Identifier e.g. table name or column name
     Identifier(String),
     /// Literal value
     Literal(String),
     /// Binary expression e.g. `1 + 2` or `fname LIKE "A%"`
-    Binary(Box<SQLExpr<ExprType>>, SQLOperator<ExprType>, Box<SQLExpr<ExprType>>),
+    Binary(Box<SQLExpr>, SQLOperator, Box<SQLExpr>),
     /// Function invocation with function name and list of argument expressions
-    FunctionCall(String, Vec<SQLExpr<ExprType>>),
+    FunctionCall(String, Vec<SQLExpr>),
     Insert,
     Update,
     Delete,
     Select,
     CreateTable,
-    /// Custom expression (vendor-specific)
-    Custom(ExprType)
 }
 
 #[derive(Debug)]
-pub enum ParserError<TokenType>
-    where TokenType: Debug + PartialEq {
-    WrongToken { expected: Vec<SQLToken<TokenType>>, actual: SQLToken<TokenType>, line: usize, col: usize },
+pub enum ParserError {
+    WrongToken { expected: Vec<SQLToken>, actual: SQLToken, line: usize, col: usize },
     Custom(String)
 }
 
-impl<TokenType> From<TokenizerError> for ParserError<TokenType>
-    where TokenType: Debug + PartialEq {
-
-    fn from(_: TokenizerError) -> Self {
-        unimplemented!()
+impl From<TokenizerError> for ParserError {
+    fn from(e: TokenizerError) -> Self {
+        ParserError::Custom(format!("{:?}", e))
     }
 }
 
 
-pub trait SQLParser<TokenType, ExprType>
-    where TokenType: Debug + PartialEq, ExprType: Debug {
-
+pub trait SQLParser {
+    fn parse_expr(&mut self) -> Result<Option<Box<SQLExpr>>, ParserError>;
     /// parse the prefix and stop once an infix operator is reached
-    fn parse_prefix(&mut self, chars: &mut CharSeq) -> Result<Option<Box<SQLExpr<ExprType>>>, ParserError<TokenType>> ;
+    fn parse_prefix(&mut self) -> Result<Option<Box<SQLExpr>>, ParserError> ;
     /// parse the next infix expression, returning None if the precedence has changed
-    fn parse_infix(&mut self, chars: &mut CharSeq, left: &SQLExpr<ExprType>, precedence: usize) -> Result<Option<Box<SQLExpr<ExprType>>>, ParserError<TokenType>>;
+    fn parse_infix(&mut self, left: &SQLExpr, precedence: usize) -> Result<Option<Box<SQLExpr>>, ParserError>;
 }
 
-pub struct PrattParser<TokenType, ExprType> {
-    pub chars: CharSeq,
-    pub parsers: Vec<Arc<Mutex<SQLParser<TokenType, ExprType>>>>
-}
-
-impl<TokenType, ExprType> PrattParser<TokenType, ExprType> where TokenType: Debug + PartialEq, ExprType: Debug {
-
-    pub fn parse_expr(&mut self) -> Result<Option<Box<SQLExpr<ExprType>>>, ParserError<TokenType>> {
-
-        for i in 0..self.parsers.len() {
-            let mut p = self.parsers[i].lock().unwrap();
-            let expr = p.parse_prefix(&mut self.chars)?;
-
-            // return as soon as we have a match
-            match expr {
-                Some(_) => return Ok(expr),
-                _ => {}
-            }
-        }
-
-        // found no valid token
-        Ok(None)
-    }
-
-}
-
-//
-//pub fn parse_expr<'a, TokenType, ExprType>(parser: Arc<Mutex<SQLParser<TokenType, ExprType>>>)
-//    -> Result<Box<SQLExpr<ExprType>>, ParserError<TokenType>> where TokenType: Debug + PartialEq, ExprType: Debug {
-//    let mut guard = parser.lock().unwrap();
-//
-//    //Result<Box<SQLExpr<ExprType>>, ParserError<TokenType>>
-//    let x = guard.parse_prefix();
-//    x
-//}
-
-
-//impl<'a, TokenType, ExprType> PrattParser<'a, TokenType, ExprType>
-//    where TokenType: Debug + PartialEq, ExprType: Debug {
-//
-//    pub fn parse_expr(&mut self) -> Result<Box<SQLExpr<ExprType>>, ParserError<TokenType>> {
-//
-//        let precedence: usize = 0;
-//        let parser_ref = self.parser.as_ref();
-//
-//        let mut expr = parser_ref.parse_prefix()?;
-//
-//        while let Some(token) = self.tokenizer.peek_token(&mut self.chars)? {
-//
-//            let next_precedence = self.tokenizer.precedence(&token);
-//
-//            if precedence >= next_precedence {
-//                break;
-//            }
-//
-//            expr = parser_ref.parse_infix(&expr, next_precedence)?.unwrap(); //TODO: fix me
-//        }
-//
-//        Ok(expr)
-//    }
-//
-//}
-
-//    fn parse_prefix(&mut self) -> Result<Box<SQLExpr>, ParserError> {
-//
-//        match self.tokenizer.peek_token()? {
-//            Some(SQLToken::Keyword(ref k)) => match k.to_uppercase().as_ref() {
-//                "INSERT" => unimplemented!(),
-//                "UPDATE" => unimplemented!(),
-//                "DELETE" => unimplemented!(),
-//                "SELECT" => unimplemented!(),
-//                "CREATE" => unimplemented!(),
-//                _ => unimplemented!()
-//            },
-//            _ => unimplemented!()
-//        }
-//        unimplemented!()
-//    }
-//
-//    fn parse_infix(&mut self, expr: Box<SQLExpr>, precedence: u8) -> Result<Box<SQLExpr>, ParserError> {
-//
-//        match self.tokenizer.next_token()? {
-//            Some(tok) => {
-//                match tok {
-//                    SQLToken::Eq | SQLToken::Gt | SQLToken::GtEq |
-//                    SQLToken::Lt | SQLToken::LtEq => Ok(Box::new(SQLExpr::Binary(
-//                        expr,
-//                        self.to_sql_operator(&tok),
-//                        self.parse_expr(precedence)?
-//                    ))),
-//                    _ => Err(ParserError::WrongToken {
-//                        expected: vec![SQLToken::Eq, SQLToken::Gt], //TODO: complete
-//                        actual: tok,
-//                        line: 0,
-//                        col: 0
-//                    })
-//                }
-//            },
-//            None => Err(ParserError::TBD)
-//        }
-//    }
-//
-//    fn to_sql_operator(&self, token: &SQLToken) -> SQLOperator {
-//        unimplemented!()
-//    }
-//
-//    fn get_precedence(&self, token: &SQLToken) -> u8 {
-//        unimplemented!()
-//    }
-//
-//    /// parse a list of SQL expressions separated by a comma
-//    fn parse_expr_list(&mut self, precedence: u8) -> Result<Vec<SQLExpr>, ParserError> {
-//        unimplemented!()
-//    }
-//
-//}
-//
-////impl GenericParser {
-////
-////    fn tokenizer(&mut self) -> &mut SQLTokenizer {
-////        &mut self.tokenizer
-////    }
-////
-////    fn parse_keywords(&mut self, keywords: Vec<&str>) -> Result<bool, ParserError> {
-////        unimplemented!()
-////    }
-////
-//////    fn parse_identifier(&mut self) -> Result<String, ParserError>;
-////
-////}
-//
-
-//
-//
-//#[cfg(test)]
-//mod tests {
-//
-//    use super::SQLToken::*;
-//    use super::*;
-//    #[test]
-//    fn parse_Acme_create_table() {
-//
-//        // CREATE TABLE test (col1 int8) HASH (col1)
-//        let tokens = vec![
-//            k("CREATE"), k("TABLE"), i("test"), LParen,
-//            i("col1"), k("int8"),
-//            RParen,
-//            k("HASH"), LParen, i("col1"), RParen
-//        ];
-//
-//        //let parser = AcmeParser { generic_parser: }
-//    }
-//    }
-//
-//    fn k(s: &str) -> SQLToken {
-//        Keyword(s.to_string())
-//    }
-//
-//    fn i(s: &str) -> SQLToken {
-//        Identifier(s.to_string())
-//    }
-//
-//
-//}
-
-
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
index 00bb0df4..73eb344f 100644
--- a/src/tokenizer.rs
+++ b/src/tokenizer.rs
@@ -70,7 +70,7 @@ pub enum TokenizerError {
 
 /// SQL Tokens
 #[derive(Debug,PartialEq)]
-pub enum SQLToken<T: Debug + PartialEq> {
+pub enum SQLToken {
     Whitespace(char),
     Keyword(String),
     Identifier(String),
@@ -89,31 +89,28 @@ pub enum SQLToken<T: Debug + PartialEq> {
     LParen,
     RParen,
     Comma,
-    /// Custom token (dialect-specific)
-    Custom(T)
 }
 
-pub trait SQLTokenizer<TokenType>
-    where TokenType: Debug + PartialEq {
+pub trait SQLTokenizer {
 
     /// get the precendence of a token
-    fn precedence(&self, token: &SQLToken<TokenType>) -> usize;
+    fn precedence(&self, token: &SQLToken) -> usize;
+
+    fn peek_token(&mut self) -> Result<Option<SQLToken>, TokenizerError>;
 
     /// return a reference to the next token and advance the index
-    fn next_token(&mut self, chars: &mut CharSeq) -> Result<Option<SQLToken<TokenType>>, TokenizerError>;
+    fn next_token(&mut self) -> Result<Option<SQLToken>, TokenizerError>;
 }
 
 
-pub fn tokenize<TokenType>(sql: &str, tokenizer: &mut SQLTokenizer<TokenType>) -> Result<Vec<SQLToken<TokenType>>, TokenizerError>
-    where TokenType: Debug + PartialEq
-    {
+pub fn tokenize(sql: &str, tokenizer: &mut SQLTokenizer) -> Result<Vec<SQLToken>, TokenizerError> {
 
     let mut chars = CharSeq::new(sql);
 
-    let mut tokens : Vec<SQLToken<TokenType>> = vec![];
+    let mut tokens : Vec<SQLToken> = vec![];
 
     loop {
-        match tokenizer.next_token(&mut chars)? {
+        match tokenizer.next_token()? {
             Some(SQLToken::Whitespace(_)) => { /* ignore */ },
             Some(token) => {
                 println!("Token: {:?}", token);