Language: Haskell Source: Rpn [] f = f rpn [h:t] f = rpn t

Question

Language: Haskell Source: Rpn [] f = f rpn [h:t] f = rpn t

(f h)

main = print $ rpn [2, 3] (+)

Errors:
source_file.hs:2:19:
Occurs check: cannot construct the infinite type: t ~ [t]
Expected type: [[t]]
Actual type: [t]
Relevant bindings include
f :: t -> t1
(bound at source_file.hs:2:11)
t :: [t]
(bound at source_file.hs:2:8)
h :: t (bound at source_file.hs:2:6)
rpn :: [[t]] -> (t -> t1) -> t -> t1
(bound at source_file.hs:1:1)
In the first argument of ‘rpn’, namely ‘t’
In the expression: rpn t (f h)

source_file.hs:2:22:
Occurs check: cannot construct the infinite type: t1 ~ t -> t1
Relevant bindings include
f :: t -> t1
(bound at source_file.hs:2:11)
t :: [t]
(bound at source_file.hs:2:8)
h :: t (bound at source_file.hs:2:6)
rpn :: [[t]] -> (t -> t1) -> t -> t1
(bound at source_file.hs:1:1)
In the second argument of ‘rpn’, namely ‘(f h)’
In the expression: rpn t (f h)

source_file.hs:4:8:
No instance for (Show (a0 -> a0 -> a0))
(maybe you haven't applied enough arguments to a function?)
arising from a use of ‘print’
In the expression: print
In the expression: print $ rpn [2, 3] (+)
In an equation for ‘main’: main = print $ rpn [2, 3] (+)

source_file.hs:4:21:
No instance for (Num [a0]) arising from the literal ‘2’
In the expression: 2
In the first argument of ‘rpn’, namely ‘[2, 3]’
In the second argument of ‘($)’, namely ‘rpn [2, 3] (+)’

source_file.hs:4:27:
No instance for (Num a0) arising from a use of ‘+’
The type variable ‘a0’ is ambiguous
Note: there are several potential instances:
instance Num Integer -- Defined in ‘GHC.Num’
instance Num Double -- Defined in ‘GHC.Float’
instance Num Float -- Defined in ‘GHC.Float’
...plus two others
In the second argument of ‘rpn’, namely ‘(+)’
In the second argument of ‘($)’, namely ‘rpn [2, 3] (+)’
In the expression: print $ rpn [2, 3] (+)

0

31.03.2019

5 ответов

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Wojciech Pawlik Автор вопроса

what have I done

0

31.03.2019

Manav | avoid unnecessary messaging me

I suppose [] is the argument list?

0

31.03.2019

Manav | avoid unnecessary messaging me

And t is the tails function?

0

31.03.2019

Manav | avoid unnecessary messaging me

Oh.. Your Base case is wrong.. If I can guess the haskell syntax, rpn [] f = [] rpn [h:t] f = (rpn t f) h f

0

31.03.2019

The Devs Bot · Accepted Answer

The Devs Bot

It looks like you posted long piece of code, consider editing it out and putting it on hastebin.com and pasting link to it instead. Alternatively, send your code in a file.

0

31.03.2019

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Language: Haskell Source: Rpn [] f = f rpn [h:t] f = rpn t

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