ghci

Defining a function signature in Haskell's interpreter GHCi doesn't work. Copying an example from this page : Prelude> square :: Int -> Int <interactive>:60:1: error: • No instance for (Show (Int -> Int)) arising from a use of ‘print’ (maybe you haven't applied a function to enough arguments?) • In a stmt of an interactive GHCi command: print it Prelude> square x = x * x How can I declare a function signature and then give function definition in Haskell interactively? also: why can't I simply evaluate the function and see its type (e.g. Prelude> square ) once it has been defined? You can

I am trying to teach myself Haskell from the book Learn You A Haskell for Great Good. I got up to the last section of chapter 7 (Modules), where it tells how to create your own module. I did a copy and paste of the Geometry module given in the book at the beginning of the section. The name of the file is Geometry.hs, as the book suggested, and the file is in the bin directory for ghci, which is where I previously was able to successfully do a load using :l for another .hs file. When I type the following command in GHCi import Geometry I get the following error: Could not find module 'Geometry'

I have this type definition: data Operace = Op (Int->Int->Int) String (Int->Int->Int) deriving Show I want to print this type into the interactive shell (GHCi). All that should be printed is the String field. I tried this: instance Show Operace where show (Op op str inv) = show str But I still keep getting No instance for (Show (Int -> Int -> Int)) arising from the 'deriving' clause of a data type declaration Possible fix: add an instance declaration for (Show (Int -> Int -> Int)) or use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When

In test.hs, I have: doubleMe x = x + x In ghci, I type: Prelude> :l test [1 of 1] Compiling Main ( test.hs, interpreted ) Ok, modules loaded: Main. *Main> doubleMe 9 <interactive>:1:0: Not in scope: `doubleMe' *Main> Why? How to fix? Are you sure that you're loading the right test.hs? Maybe you're in the wrong directory. Or maybe you didn't save test.hs after adding the definition of doubleMe. My guess is that you have defined a main function in your source file. If you have defined a main function, loading the module with :l test won't import any functions but main . In that case you can load