NB. Definitions used in Data Structures Chapter
NB. Stacks

NB. A cluge to fix broken object code as stddefs locale
NB. now contains the definitions in stddefs.ijs
make_z_ 'stddefs.ijs'

stack_tag =: box 'stack'
the_empty_stack =: box stack_tag

make_stack =: monad def 'the_empty_stack'

stackp =: monad def 'stack_tag match first open y'

empty_stackp =: monad def 'the_empty_stack match y'

push_stack =: monad define
('item obj') =. y
if. not stackp box obj
  do. error 'wrong type second input to push_stack' ; obj
  else. box obj append box item
end.
)

top_stack =: monad define
if. not stackp y
  do. error 'wrong type input to top_stack' ; y
  else. open last open y
end.
)

pop_stack =: monad define
if. not stackp y
  do. error 'wrong type input to pop_stack' ; y
  else. box drop_last open y
end.
)

size_stack =: monad define
if. not stackp y
  do. error 'wrong type input to size_stack' ; y
  else. _1 + tally open y
end.
)

print_stack =: monad define
if. not stackp y
    do. error 'wrong type input to print_stack' ; y
  elseif. 0 = size_stack y
    do. 'end of stack'
  elseif. 1
    do. display top_stack y
        print_stack pop_stack y
end.
)

NB. Queues

queue_tag =: box 'queue'
the_empty_queue =: box queue_tag

make_queue =: monad def 'the_empty_queue'

queuep =: monad def 'queue_tag match first open y'

empty_queuep =: monad def 'the_empty_queue match y'

enter_queue =: monad define
('item queue') =. y
if. not queuep box queue
  do. error 'wrong type second input to enter_queue' ; queue
  else. box queue_tag append (box item) append rest queue
end.
)

front_queue =: monad define
if. not queuep y
  do. error 'wrong type input to front_queue' ; y
  else. open last open y
end.
)

remove_queue =: monad define
if. not queuep y
  do. error 'wrong type input to remove_queue' ; y
  else. box drop_last open y
end.
)

size_queue =: monad define
if. not queuep y
  do. error 'wrong type input to size_queue' ; y
  else. _1 + tally open y
end.
)

print_queue =: monad define
if. not queuep y
    do. error 'wrong type input to print_queue' ; y
  elseif. 0 = size_queue y
    do. 'end of queue'
  elseif. 1
    do. display front_queue y
        print_queue remove_queue y
end.
)

NB. A simple list application


people =: ('howland' ; 'jack' ; 'computer science professor') ; ('clinton' ; 'bill' ; 'president usa') ; ('clinton' ; 'hillary' ; 'president usa') ; ('perot' ; 'ross' ; 'wanted to be president') ; < ('bush' ; 'george' ; 'used to be president')

lookup =: monad define
('name database') =. y
if. 0 = tally database
  do. ''
  else. if. name match head head database
          do. head database
          else. lookup name ; box rest database
        end.
end.
)

lookup =: monad define
('name database') =. y
if. nullp database
  do. ''
  else. if. name match head head database
          do. head database
          else. lookup name ; box rest database
        end.
end.
)