Of Monads and Men

module Temperature (tempToC, tempToF) where

{- Implement the function `tempToC` to convert
`  Fahrenheit to Celsius                    -}

tempToC x=(x- 32) / 1.8.

{- Implement the function `tempToF` to convert
`  Celsius to Fahrenheit                    -}

tempToF x=x* 1.8 + 32.

oh i know

why is this bad also?

module Temperature (tempToC, tempToF) where
tempToC x=ceiling ((x- 32) / 1.8)
tempToF x=x* 1.8 + 32

@UnrelatedString

Wheat Wizard

11:58 AM

@NumberBasher That compiles fine for me.

Number Basher

[1 of 2] Compiling Paths_temperature
[2 of 2] Compiling Temperature

/mnt/exercism-iteration/src/Temperature.hs:2:1: warning: [-Wmissing-signatures]
Top-level binding with no type signature:
tempToC :: (RealFrac a, Integral b) => a -> b
|
2 | tempToC x=ceiling ((x- 32) / 1.8)
| ^^^^^^^

/mnt/exercism-iteration/src/Temperature.hs:3:1: warning: [-Wmissing-signatures]
Top-level binding with no type signature:
tempToF :: Fractional a => a -> a
|
3 | tempToF x=x* 1.8 + 32
| ^^^^^^^
Preprocessing test suite 'test' for temperature-1.0.0.0..

exercism.org/tracks/haskell/exercises/temperature/edit

> >>> 12894712893012**1294871209382
> Infinity

That's not as good as Python

;-)

> >>> 2**10
> 1024.0

This took me by surprise -- Why the .0?

Wheat Wizard

The problem is in your test not the code you posted.

There are also some warnings, which you probably want to resolve but that don't actually block development.

Number Basher

what problem is there? thnx

Wheat Wizard

If you resolve the types the error in your tests should probably present itself.

The warnings are because the functions tempToC and tempToF don't have type signatures.

The compiler can figure things out when things are good, but if you tell the compiler what types you expect then it gives more useful errors when things go wrong.

Number Basher

how do i go back to the script exercium gave me?

Oh I got it

h m m

module Temperature (tempToC, tempToF) where

{- Implement the function `tempToC` to convert
`  Fahrenheit to Celsius                    -}

tempToC :: Integer -> Float
tempToC x = ((x- 32) / 1.8)


{- Implement the function `tempToF` to convert
`  Celsius to Fahrenheit                    -}

tempToF :: Float -> Integer
tempToF x = ceiling((x* 1.8 + 32))

[1 of 2] Compiling Paths_temperature
[2 of 2] Compiling Temperature

/mnt/exercism-iteration/src/Temperature.hs:7:14: error:
    • Couldn't match expected type ‘Float’ with actual type ‘Integer’
    • In the expression: ((x - 32) / 1.8)
      In an equation for ‘tempToC’: tempToC x = ((x - 32) / 1.8)
  |
7 | tempToC x = ((x- 32) / 1.8)
  |              ^^^^^^^^^^^^^

--  While building package temperature-1.0.0.0 (scroll up to its section to see the error) using:
      /opt/test-runner/.stack/setup-exe-cache/x86_64-linux-tinfo6/Cabal-simple_mPHDZzAJ_3.0.1.0_ghc-8.8.4 --builddir=.stack-work/…

Don't understand...

(make sure you ping me in your reply thnx

Wheat Wizard

12:10 PM

(-) :: Num a => a -> a -> a
(/) :: Fractional a => a -> a -> a

@NumberBasher These are the two functions you use. Do you know how to read their types?

Number Basher

erm well no

Wheat Wizard

Ok no problem let me explain them.

Number Basher

what did i lose in the tutorial

Wheat Wizard

(-) takes two numbers of the same type and produces another number of that type (by subtracting). (/) takes two fractionals of the same type and produces another fractional of that type.

Number Basher

yah

that's true for most langs...

even tho i don't why
(-) :: Num a => a -> a -> a
(/) :: Fractional a => a -> a -> a
means that

Wheat Wizard

12:13 PM

So you say your code takes an integer and produces a float, but both (-) and (/) produce results with the same type as their input.

Number Basher

so i need to float it?

Wheat Wizard

Yes.

Don't worry too much about being able to read the types right now, you will learn.

Number Basher

7 | tempToC x = ((x- 32.0) / 1.8)
  |              ^^^^^^^^^^^^^^^

Why?

Wheat Wizard

The x is still an Integer, since your type signature says so 32 was not the issue.

 tempToC x = (fromInteger x - 32) / 1.8

Number Basher

oh

why does this not work

((x- 32.0) / 1.8)

still an int?

Wheat Wizard

12:17 PM

It does work.

It just doesn't work with your type signature.

Number Basher

Hmm...

Golfing must be hard

Wheat Wizard

Golfing is fun and not very hard.

But dealing with floats is often a bit annoying.

Number Basher

is there a shorter way

fromIntegral will else take about 20% of the answer

Wheat Wizard

Yeah, fromInteger is 1 byte shorter but not all that much better.

The solution would be try to take a float instead since that's the type we want to output.

But it's not always possible.

Number Basher

i just typed this

isLeapYear x = not x%4and x%100or not x%400

i'm so stupid

hahaha

Wheat Wizard

12:22 PM

Modulo is the mod function. And there are no implicit type conversions.

Number Basher

oh no

let's hope this ugly rubbish works

isLeapYear x = not fromIntegral mod x 4 && fromIntegral mod x 100 || not fromIntegral mod x 400

Wheat Wizard

Definitely not.

Your operator precedence is pretty messed up, and fromIntegral is not going to cast to Bool.

Number Basher

oh no

[1 of 2] Compiling LeapYear

/mnt/exercism-iteration/src/LeapYear.hs:4:16: error:
• Couldn't match expected type ‘(Integer -> Integer -> Integer)
-> Integer -> Integer -> Bool’
with actual type ‘Bool’
• The function ‘not’ is applied to four arguments,
but its type ‘Bool -> Bool’ has only one
In the first argument of ‘(&&)’, namely ‘not fromIntegral mod x 4’
In the first argument of ‘(||)’, namely
‘not fromIntegral mod x 4 && fromIntegral mod x 100’
|
4 | isLeapYear x = not fromIntegral mod x 4 && fromIntegral mod x 100 || not fromIntegral mod x 400

Given a year, report if it is a leap year.

The tricky thing here is that a leap year in the Gregorian calendar occurs:

on every year that is evenly divisible by 4
except every year that is evenly divisible by 100
unless the year is also evenly divisible by 400

Wheat Wizard

Instead just say what you want without any dirty hacks. mod x 4 == 0

Number Basher

How do I do this?

Wheat Wizard

12:25 PM

isLeapYear x = (mod x 4 == 0) && (mod x 100 /= 0) || (mod x 400 == 0)

Number Basher

ghci> 5 /= 5
False

both works?

/=, !

!=

Wheat Wizard

No just /=

Number Basher

i would much rather not it

Wheat Wizard

Ok, I'm not sure why but you can do that.

Number Basher

because != /= everything confusing

i suppose you don't have += like in Pyothon?

Wheat Wizard

12:29 PM

Thank god no.

in The Nineteenth Byte, Mar 12, 2017 at 19:06, by Wheat Wizard

CMC: Without running it, guess what this python snippet prints.
a=[1,2,3]
a[-1]+=a.pop()
print a

Haskell doesn't have mutable state so it avoids stuff like +=.

Number Basher

@WheatWizard i suppose that is python2?

Wheat Wizard

Yes, but you can add parentheses and it does the same thing in Python 3 as well.

Number Basher

>>> a=[1,2,3]
>>> a[-1]+=a.pop()
>>> print a
[1, 6]

why?

i think i understand

based on this

>>> a=[1,2,3]
>>> a[-1]=a[-1]+a.pop()
>>> a
[1, 6]
>>>
>>> a=[1,2,3]
>>> a[-1]=a.pop()+a[-1]
>>> a
[1, 5]

Wheat Wizard

Yeah.

Number Basher

> Given an age in seconds, calculate how old someone would be on:

Mercury: orbital period 0.2408467 Earth years
Venus: orbital period 0.61519726 Earth years
Earth: orbital period 1.0 Earth years, 365.25 Earth days, or 31557600 seconds
Mars: orbital period 1.8808158 Earth years
Jupiter: orbital period 11.862615 Earth years
Saturn: orbital period 29.447498 Earth years
Uranus: orbital period 84.016846 Earth years
Neptune: orbital period 164.79132 Earth years

I don't understand the input method

Wheat Wizard

12:38 PM

hm. Hard to tell, maybe it's an integer.

Number Basher

so it gets a[-1] which is 3 and then pops it which is 3 again, adds it to get 6, and then now a is [1,2] and now we set a[-1]=6 which makes it [1,6] ok makes sense

> Instructions
Given an age in seconds, calculate how old someone would be on:

Mercury: orbital period 0.2408467 Earth years
Venus: orbital period 0.61519726 Earth years
Earth: orbital period 1.0 Earth years, 365.25 Earth days, or 31557600 seconds
Mars: orbital period 1.8808158 Earth years
Jupiter: orbital period 11.862615 Earth years
Saturn: orbital period 29.447498 Earth years
Uranus: orbital period 84.016846 Earth years
Neptune: orbital period 164.79132 Earth years
So if you were told someone were 1,000,000,000 seconds old, you should be able to say that they're 31.69 Earth-years old.

module SpaceAge (Planet(..), ageOn) where

data Planet = Mercury
            | Venus
            | Earth
            | Mars
            | Jupiter
            | Saturn
            | Uranus
            | Neptune

ageOn :: Planet -> Float -> Float
ageOn planet seconds = error "You need to implement this function."

Wheat Wizard

Ok so it's a number years maybe?

Number Basher

ageOn planet seconds = planet * seconds?

• Couldn't match expected type ‘Planet’ with actual type ‘Float’
• In the second argument of ‘(*)’, namely ‘seconds’
In the expression: planet * seconds
In an equation for ‘ageOn’: ageOn planet seconds = planet * seconds
|
13 | ageOn planet seconds = planet * seconds
| ^^^^^^^

-- While building package space-age-1.2.0.6 (scroll up to its section to see the error) using:
/opt/test-runner/.stack/setup-exe-cache/x86_64-linux-tinfo6/Cabal-simple_mPHDZzAJ_3.0.1.0_ghc-8.8.4 --builddir=.stack-work/dist/x86_64-linux-tinfo6/Cabal-3.0.1.0 build lib:space-age test:tes…

ohh great. sarcasm

i mean

Wheat Wizard

Do you understand the error?

Number Basher

no

but i think it tells me he can't * a planet

Wheat Wizard

12:44 PM

Yes, you can only multiply two things of the same type (they also have to be numbers).

Planets are not numbers so you can't use (*) on them.

Do you know how to do pattern matching?

Number Basher

then how?

no...?

Wheat Wizard

ageOn :: Planet -> Float -> Float
ageOn Jupiter earthAge = 2.3 * earthAge
ageOn Mars earthAge = 4.3 * earthAge
ageOn Venus earthAge = 9.5 * earthAge
...

You can define different cases of your function each on their own line.

Number Basher

ok thanks

why?

wieuhiehjdisjowhuiewhiwco$ ghci
-bash: ghci: command not found

i just installed it, it works

and then i restart the terminal

why

sudo: apt-get: command not found

what

Wheat Wizard

hmmm

Number Basher

i have a macos fyi

Wheat Wizard

12:51 PM

Ah.

why are you running apt-get?

Number Basher

when i first installed if i used

curl --proto '=https' --tlsv1.2 -sSf get-ghcup.haskell.org | sh

Wheat Wizard

Ah well yeah that shell script is probably for linux.

Number Basher

brew install might work *praying

Wheat Wizard

It should.

Number Basher

@WheatWizard yep

not working is the whole point of programming

(not)

@WheatWizard 25% now

50%...

75%...

pouring...

c u tmr (my tmr is in china

now it works!!! @WheatWizard

Wheat Wizard

1:07 PM

Nice.

Number Basher

1:50 PM

back

i wrote this

ageOn Mercury Earthyears=0.2408467 * Earthyears
ageOn Venus Earthyears=0.61519726 * Earthyears
ageOn Earth Earthyears=1.0 * Earthyears
ageOn Mars Earthyears=1.8808158 * Earthyears
ageOn Jupiter Earthyears=11.862615 * Earthyears
ageOn Saturn Earthyears=29.447498 * Earthyears
ageOn Uranus Earthyears=84.016846 * Earthyears
ageOn Neptune Earthyears=164.79132 * Earthyears

i think it is unallowed to use Earthyears as the variable name

wrote this

ageOn :: Planet -> Float -> Float
ageOn Mercury years=0.2408467 * years
ageOn Venus years=0.61519726 * years
ageOn Earth years=years
ageOn Mars years=1.8808158 * years
ageOn Jupiter years=11.862615 * years
ageOn Saturn years=29.447498 * years
ageOn Uranus years=84.016846 * years
ageOn Neptune years=164.79132 * years

told me this

space-age> test (suite: test)


ageOn
  Earth FAILED [1]

Failures:

  test/Tests.hs:27:26:
  1) ageOn Earth
       expected: 31.69
        but got: 1.0e9

  To rerun use: --match "/ageOn/Earth/"

Randomized with seed 585517182

Finished in 0.0003 seconds
1 example, 1 failure

space-age> Test suite test failed
Completed 2 action(s).
Test suite failure for package space-age-1.2.0.6
    test:  exited with: ExitFailure 1
Logs printed to console

why?

@WheatWizard

oh

> Given an age in seconds

ageOn :: Planet -> Float -> Float
ageOn Mercury years= years/0.2408467           /60/60/24/365.25
ageOn Venus years=1/0.61519726 * years        /60/60/24/365.25
ageOn Earth years=years                      /60/60/24/365.25
ageOn Mars years=1/1.8808158 * years        /60/60/24/365.25
ageOn Jupiter years=1/11.862615 * years    /60/60/24/365.25
ageOn Saturn years=1/29.447498 * years    /60/60/24/365.25
ageOn Uranus years=1/84.016846 * years   /60/60/24/365.25
ageOn Neptune years=1/164.79132 * years /60/60/24/365.25

This did it

yay

I just found this

ageOn :: Planet -> Float -> Float
13
ageOn p s = s / (31557600.0 * planetMultiplier)
14
  where
15
    planetMultiplier = case p of
16
      Earth   ->   1.0
17
      Mercury ->   0.2408467
18
      Venus   ->   0.61519726
19
      Mars    ->   1.8808158
20
      Jupiter ->  11.862615
21
      Saturn  ->  29.447498
22
      Uranus  ->  84.016846
23
      Neptune -> 164.79132

condiserably better

chat.stackexchange.com/rooms/info/136370/haskell?tab=general

let's put this there actually

bye for now

This Might Be a Room

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