Ord t
type t must support ordering/comparison
18 Matching Annotations
- Sep 2026
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tgdwyer.github.io tgdwyer.github.io
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filter
function
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An essential thing to know before trying to type in the above function is that Haskell delimits the scope of multi-line function definitions (and all multiline expressions) with indentation
Haskell uses indentation to know which lines belong to a block code
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IO monad
a computation that can perform input/perform
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() (called unitA type with exactly one value, (), used to indicate the absence of meaningful return value, similar to void in other languages. )
void in Java / C / TypeScript
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tgdwyer.github.io tgdwyer.github.io
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Tail Call Optimisation
normal recursion creates a new stack frame for every recursive call. Tail recursion can be converted by the compiler into a loop, so it doesn't keep growing the stack
TCO does not means faster, its just for reducing stack usage
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Exercise What other functions called in the JavaScript code generated for the above definition of main are curried? Why?
add x y = x + y
Currying allows a function to receive arguments one at a time, which enables partial application and makes functions eaiser to reuse and compose
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Exercise If one didn’t happen to like the fact that function chaining with the $ operator reads right to left, how would one go about creating an operator that chains left to right? (Hint: infixl is a thing and you will need to make a slightly different apply function also).
operator called |>
x |> f === f x
opposite orientation of $
as $ uses apply f x = f x
x |> f becomes applyLeft x f = f x
Ans: infixl 0 applyLeft as |>
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in Haskell, putting the argument after the function left-to-right unless operators change the grouping
replace every $ with brackets main = log $ show $ map fibs $ 1..10 equivalent to main = log (show (map fibs (1..10)))
map fibs (1..10) apply fibs to every number in the list
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pattern matchingA mechanism in functional programming languages to check a value against a pattern and to deconstruct data. ,
fibs 0 = 1 ^ ^ ^ | | | | | result | pattern function
Haskell commonly uses pattern matching instead of writing if/else for cases where the input's structure or value determines what to do.
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edstem.org edstem.org
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cannot till Dirt on an adjacent tile.
only can change the current Dirt that the farmer is stepping on
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The game must then show the Farmer's current HP, SP, and inventory contents, as in the following example:
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cannot fall below zero or exceed the maximum of 20
BaseStatistic helps to do this
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REQ1 Heath points (HP) = hit point which is in Farmer constructor
GameEntity class is used to control the actor's statistic
unconscious(map) removes the Farmer from the map
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At the start of each Farmer turn, the Farmer regenerates 1 SP before the action menu is displayed.
add in tick()
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at 0 HP, they die.
this is check in isConscious() inside farmer's playTurn()
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edstem.org edstem.org
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High-level modules should not depend on low-level modules. Both should depend on abstractions. Abstractions should not depend upon details. Details should depend on abstractions.
Depend on abstractions rather than concrete implementation
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edstem.org edstem.org
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Liskov Substitution Principle
A child/subclass should be able to replace its parent/superclass without breaking the program's expected behaviour.
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