22.03.16 - Interactive Programming

So far seen how Haskell can be used to write batch programs. Today, will see how to do interactive programs

Problem: Haskell programs have no side effects However interactive programs have side effects

Solution: Can be written in Haskell by using types to distinguish pure expressions from impure actions that may involve side effects IO a - returns the value of type a

Basic Actions

getCharAdjugate - reads a character from the keyboard, echos it to the screen and returns the character as a result putChar c - writes the character c to the screen and returns no result value return v - returns the value v without performing any interaction

Sequencing

Sequence of actions can be combined as a single composite action using the keyword do

Derived Primitives

getLine - reads an entire string. Haskell reads each character one by one, then returns it as a list. Need to have an action in the do block putStr - Writes a string to the screen putStrLn - Writes a string and moving to a new line

Evaluating an action executes its side effects, with the final result value being discarded