Language "IBAFlang"
    
Syntax START:start ::= statement*
Semantics start[[ _:start ]] : =>null-type
Rule start[[ Stmt* ]] = initialise-binding execute-block[[ Stmt* ]]





Lexis keyword ::= 'else' | 'false' | 'if' | 'true' | 'while' | 'int'
Lexis SDF
/*
lexical syntax 
  ``id`` = ``keyword`` {reject}
lexical restrictions
  ``id`` -/- [A-Za-z0-9]
*/