BNF
---

program = definitions expression 

definitions = definition definitions | e

definition = identifier identifiers = expression ; 

identifiers = identifier identifiers | e 

expression = identifier atomicExpressions | atomicExpression 

atomicExpressions = atomicExpression atomicExpressions | e

atomicExpression = number | ( expression ) 


Abstract Syntax
---------------

module Syntax where 

data Program = Program [Definition] Expression

data Definition = Definition Identifier [Identifier] Expression

data Expression = Number Int 
                | Application Identifier [Expression]

type Identifier = String