Perk.Free_variablesFunctions for computing the free variables of commands and expressions
val free_variables_command :
Ast.command_a ->
Ast.perkident list * Ast.perkident listReturns pair of lists: FIRST LIST IS FREE VARS, SECOND LIST IS BOUND
val free_variables_expr : Ast.expr_a -> Ast.perkident list * Ast.perkident listReturns pair of lists: FIRST LIST IS FREE VARS, SECOND LIST IS BOUND
val list_minus : Ast.perkident list -> Ast.perkident list -> Ast.perkident list