Consider the following PureScript code, which is trying to convert a Number into an Integer.
module Main where
import Prelude (discard, Unit)
import Prelude (($))
import Data.Int ( toStringAs, fromNumber, decimal )
import Data.Maybe ( fromMaybe )
myNumber :: Number
myNumber = 4.762
myInteger :: Int
myInteger = fromMaybe (0 $ (fromNumber myNumber))
However this code produces the following error,
Could not match type
Int
with type
t0 -> t1
Not sure how to use fromMaybe correctly here as this use case doens't seem to be documented yet.
So the question is, What is the correct syntax for converting a number to an integer?
It's not 100% clear what you're trying to do, but it kinda looks like you have an extra set of parens.
myInteger = fromMaybe (0 $ (fromNumber myNumber))
^ ^
| |
these two are detrimental
The expression inside these two parens is:
0 $ (...)
If you look at the definition or the docs for the $ operator, you'll see that its left argument is supposed to be a function.
right argument
|
v
0 $ (...)
^
|
left argument
But PureScript sees a 0 (of type Int) instead of a function.
And so it rightly complains: cannot match type Int with type (function type)
What I'm guessing you actually meant is to (1) try to convert the Number to an Int with fromNumber, and (2) if that fails, substitute zero with fromMaybe.
If you look at the definition of fromMaybe, you'll see that it has two arguments: first argument is the default value and second argument is the Maybe value. So all you need to do is just call fromMaybe with those two arguments:
second argument
|
------------------
/ \
v v
myInteger = fromMaybe 0 (fromNumber myNumber)
^
|
first argument
I really don't understand how you could possibly get the idea of writing 0 $ (...), so I cannot address that particular misunderstanding, sorry.