forked from steger/pr3-sose2026
69 lines
3.0 KiB
Markdown
69 lines
3.0 KiB
Markdown
# Haskell - Expressions
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The following illustrates some haskell basics. It can be reproduced using `ghci`.
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## Types, Literals, and Constants along with Arithmetic and Boolean Operations
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Expression | Type (:t) | Value | Comment
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--- | --- | --- | --------
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`2` | `Num a => a` | `2` |
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`2.03` | `Fractional a => a` | `2.3` |
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`'c'` | `Char` | `'c'`
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`"hallo"` | `String` | `"hallo"` |
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`True` | `Bool` | `True` |
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`x=5` | `Num a => a` | `5` | Constant named `x`
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`2 + 3` | `Num a => a` | `5` | Similar `-,*,^`
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`2 / 3` | `Fractional a => a` | `0.6666666666666666` |
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`1 > 2` | `Bool` | `False` | Similar `<, <=, >=, ==, /=`
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`True && False` | `Bool` | `False` | Similar `\|\|,not`
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`((2+3)*5 > 1) \|\| not (1 > 2)` | `Bool` | `True` | Right part is not evaluated due to lazy evaluation
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## Unary Functions
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Expression | Type (:t) | Value | Comment
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--- | --- | --- | --------
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`sqrt(4)` | `Floating a => a` | `2.0` |
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`sqrt 4` | `Floating a => a` | `2.0` | Similar `abs,negate,signum,recip`
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`sqrt` | `Floating a => a -> a` | |
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`sqrt 3^2 + 4^2` | `Floating a => a` | `19.0` |
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`sqrt (3^2 + 4^2)` | `Floating a => a` | `5.0` |
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`negate(sqrt (3^2 + 4^2))` | `Floating a => a` | `-5.0` |
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`negate $ sqrt (3^2 + 4^2)` | `Floating a => a`| `-5.0` | Function **application** operator `$`
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`(negate . sqrt) (3^2 + 4^2)`| `Floating a => a`| `-5.0` | Function **composition** operator `.` Reads `negate` **after** `negate . sqrt` |
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`(negate . length) "hallo"` | `Int` | `-5` |
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`negatedRoot = negate . sqrt` | `Floating c => c -> c` | | Constant named `negatedRoot`
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## Binary Functions
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Expression | Type (:t) | Value | Comment
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--- | --- | --- | --------
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`div 8 4` | `Integral a => a` | `2` | Similar `mod,gcd,lcm,not`
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``8 `div` 4`` | `Integral a => a` | `2` | **Infix** notation using backticks
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`8 + 4` | `Num a => a` | `12` | `-,*,^,<, <=, >=, ==, /=`
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`(+) 8 4` | `Num a => a` | `12` | **Prefix** notation using parenthesis
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`div` | `Integral a => a -> a -> a` | | **Currying** represents multi-argument functions as a chain of single-argument functions |
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`div 8` | `Integral a => a -> a` | | binds the **first** argument; Similar `(8/),(8*),(8+),(8-)` |
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`div8bySomething = div 8` | `Integral a => a -> a` | |
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`div8bySomething 4` | `Integral a => a` | `2` |
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`uncurry div` | `Integral c => (c, c) -> c` | | accepts a single tuple argument
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`uncurry div (8,4)` | `Integral c => c` | `2` |
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`uncurry` | `(a -> b -> c) -> (a, b) -> c`| |
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`` (`div` 4) `` | `Integral a => a -> a` | | **Sectioning** binds the **second** argument of infix functions; Similar `(/8),(*8),(+8),(-8)` |
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``divSomethingBy4 = (`div` 4)`` | `Integral a => a -> a` | |
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`divSomethingBy4 8` | `Integral a => a` | `2` |
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## Tuples
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Expression | Type (:t) | Value | Comment
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--- | --- | --- | --------
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`(1, 2)` | `(Num a, Num b) => (a, b)` | `(1, 2)` |
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`(1, "hello", True)` | `(Num a => (a, String, Bool)` | `(1, "hello", True)` |
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`fst (1, 2)` | `Num a => a` | `1` |
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`snd (1, 2)` | `Num b => b` | `2` |
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`(,) 1 2` | `Num a => a -> a -> (a, a)` | `(1, 2)` |
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## Strings
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## Control Structures
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## Lists |