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INT stacksize = 8.
TYPE dataitem = NEW datum/(0..255),
data = NEW (somedata&dataitem |nodata),
exception= NEW (ok |stackoverflow |stackunderflow |full),
stack_pointer = NEW point/(1..stacksize).
FN S_P_REGISTER = (stack_pointer) -> stack_pointer:
DELAY (p&point/1,1).
FN OVERFLOW_REGISTER = (exception) -> exception:
DELAY (ok,1).
FN MEMORY = ([stacksize]data) -> [stacksize]data:
DELAY ([stacksize]nodata,1).
FN STACK = ([stacksize]data: a, exception: b,stack_pointer: c) ->
([stacksize]data, exception, stack_pointer):
(MEMORY a, OVERFLOW_REGISTER b, S_P_REGISTER c).
TYPE contrl = NEW (push |pop |donothing).
FN INCR = (stack_pointer: number) -> stack_pointer:
CASE number
OF p&point/stacksize: full
ELSE (
FN INC = (pointer: num) -> pointer: ARITH num+1.
LET inc = INC (number//p).
OUTPUT p&inc
)
ESAC.
FN DECR = (stack_pointer: number) -> stack_pointer:
CASE number
OF full: p&point/stacksize
ELSE (
FN DEC = (pointer: num) -> pointer: ARITH num-1.
LET dec = DEC (number//p).
OUTPUT p&dec
)
ESAC.
FN PUSH = (data: dataelement, [stacksize]data: memory,
stack_pointer: s_p_register) -> [stacksize]data:
BEGIN SEQ
VAR mem := [stacksize]nodata;
mem := memory;
mem [[s_p_register//p]] := dataelement;
OUTPUT mem
END.
FN LIFO = (data: dataelement, contrl: push_or_pop)
-> (data, exception):
(
MAKE STACK: stack.
LET memory = stack[1],
overflow_register = stack[2],
s_p_register = stack[3].
JOIN CASE push_or_pop
OF pop: CASE sp_p_register
OF p&point/1: (memory, stackunderflow, s_p_register)
ELSE (memory, ok, DECR s_p_register)
ESAC,
push: CASE s_p_register
OF full: (memory, stackoverflow, s_p_register)
ELSE (PUSH(dataelement,memory,s_p_register),
ok, INCR s_p_register)
ESAC,
donothing: (memory, ok, s_p_register)
ESAC
-> stack.
OUTPUT (memory [[(DECR s_p_register)//p]], overflow_register)
).
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