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Haskell

A* Shortest Path in Haskell

• A* Shortest Path in Haskell

Order of parameters and currying

• Type definitions with -> operator is right associative.
• Function calls with parameters separated by space (” “) are left associative.
• Parameters are ordered from left to right both in type definitions and function calls.

For example see the type definition of div.

> :t div
:: (Integral a) => a -> a -> a

• Numbering the parameters, a1 -> a2 -> a3
• Using right associative rule for -> operator, a1 -> (a2 -> a3)

So the type definition roughly translates to:

1. A value of a1 applied to function div evaluates a function
2. A value of type a2 applied to this function evaluates to a value of type a3

Calling divwith parameters 10 and 2 give the result 5.

> div 10 2
=> 5

• Using left associative rule for parameters in function calls, (div 10) 2

This means that the function returned by applying 10 to div translates to 10/x. 2 applied to this function evaluates to 5. 10 is of type a1, 2 of type a2 and 5 of type a3.

The infix operator of div works in the same manner.

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

> (/) 10 2
=> 5.0

> 10 / 2
=> 5.0

> 10 `div`  2
=> 5

References

• http://www.haskell.org
• A Gentle Introduction To Haskell, version 98
• UNIX tools written in Haskell
• Parsing in Haskell
• Haskell Quick Reference
• pandoc
• Functional Flocks
• Gloss
• Haskell Cheat Sheet - Very good but not complete
• Haskell Web Frameworks - Salvia, Scotty and Warp etc.
• Monad is not difficult - I still think this is really hard to grok …
• Understanding Haskell Monads - is very thorough and makes it easier …