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Lab 6 -- Location Tags

Adapt from https://pages.github.khoury.northeastern.edu/2500/2024F/lab/lab11.html

The goal of this lab will be to build many functions related to tracking tags.

Given Data Definitions​

A PhoneId is a String​

Interpretation: a unique identifier for a person's phone

Examples:

PHONE1 = "p1"
PHONE2 = "p2"

Template:

fun phone-id-temp(pi :: String) -> Any:
  ... pi ...
end

A TagId is a String​

Interpretation: a unique identifier for a tracking tag

Examples:

TAG1 = "t1"
TAG2 = "t2"
TAG3 = "t3"

Template:

fun tagid-temp(ti :: String) -> Any:
  ... ti ...
end

An Owner is a:​

data Owner:
  | owner(phoneid :: String, tagid :: String)
end

Interpretation: a record of a particular phone owning a tracking tag. There should only ever be one phone per tag, though can be many tags per phone.

Examples:

OWNER1 = owner(PHONE1, TAG1)
OWNER2 = owner(PHONE1, TAG2)
OWNER3 = owner(PHONE2, TAG3)

Template:

fun owner-temp(o :: Owner) -> Any:
  ... o.phoneid ... o.tagid ...
end

A Time is a Number​

Interpretation: a time represented by the number of seconds since Jan 1, 2025.

Examples:

TIME1 = 10
TIME2 = 20
TIME3 = 30

Template:

fun time-temp(t :: Number) -> Any:
  ... t ...
end

An Encounter is a:​

data Posn:
  | posn(x :: Number, y :: Number)
end
data Encounter:
  | encounter(phoneid :: String, tagid :: String, time :: Number, posn :: Posn)
end

Interpretation: a record of a tag being seen by a given phone at a given time and location. Note that location is represented as X,Y coordinates for simplicity.

Examples:

ENCOUNTER1 = encounter(PHONE1, TAG1, TIME1, posn(0, 0))
ENCOUNTER2 = encounter(PHONE2, TAG1, TIME2, posn(100, 100))
ENCOUNTER3 = encounter(PHONE1, TAG2, TIME3, posn(0, 0))

Template:

fun encounter-temp(e :: Encounter) -> Any:
  ... e.phoneid ... e.tagid ... e.time ... e.posn ...
end

Problem 1​

Design a function tag-activity-count that takes a TagId, a List<Encounter>, a start Time, and an end Time, and calculates how many times the tag has been encountered between the two times, including encounters at exactly the start and end times. Assume that the second time is greater than the first.

Problem 2​

Design a function tag-encounter-position that identifies all positions (0-indexed) where a specific TagId appears within a list of Encounters. If the tag id does not occur, the list may be empty.