List comprehension

syntactic sugar to apply set operations to lists
syntax := “[” output expression “|” variable / binding = input set “,” predicate “]”
e.g. [ 1 / x | x ← [-1, -0.75 .. 1], x /= 0 ]
- creates a list
  - of reciprocal numbers (1 / x)
  - from the set {-1, -0.75, -0.5, -0.25, 0, 0.25, 0.5, 0.75, 1} ([-1,-0.75..1])
  - except 0 (x /= 0)
- code:
```
main :: IO ()
main = print x
 
x = [ 1 / x | x <- [-1,-0.75..1], x /= 0 ]
```
  - excutes, with output:
```
[-1.0,-1.3333333333333333,-2.0,-4.0,4.0,2.0,1.3333333333333333,1.0]
```

binding can be applied to pattern matching to filter out sums

example:

import Prelude hiding (Maybe(..))
 
main :: IO ()
main = print x
 
data Maybe a = Just a | Nothing
 
x = [ch | (Just ch) <- [Just '3', Nothing, Just '4']]

excutes, with output:
```
"34"
```

List comprehension

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