OK, then there's also an implicit *in* after the *let* in this code. Must the implicit (or explicit) *in* actually use the calculated value(s)?
And, the monad can "continue on" after the *let* (with or without the *in*) as below, i.e., the *let* needn't be the last statement in the *do*?
main = do
gen <- getStdGen
let code = genCode gen
putStrLn $ "Code is " ++ show code
putStrLn "..."
Michael
--- On Tue, 8/10/10, Job Vranish wrote:
From: Job Vranish
Subject: Re: [Haskell-cafe] Couple of questions about *let* within *do*
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Tuesday, August 10, 2010, 12:52 PM
Yes, and yes :)
For example:
import Data.Char
main = do
let prompt s = do
putStrLn s
getLine
firstName <- prompt "What's your first name?"
lastName <- prompt "What's your last name?"
let bigFirstName = map toUpper firstName
bigLastName = map toUpper lastName
putStrLn $ "hey " ++ bigFirstName ++ " " ++ bigLastName ++ ", how are you?"
- Job
On Tue, Aug 10, 2010 at 12:40 PM, michael rice wrote:
From: Learn You a Haskell
===================
Remember let bindings? If you don't, refresh your memory on them by reading this section. They have to be in the form of let bindings in expression, where bindings are names to be given to expressions and expression is the expression that is to be evaluated that sees them. We also said that in list comprehensions, the in part isn't needed. Well, you can use them in do blocks pretty much like you use them in list comprehensions. Check this out:
import Data.Char
main = do
putStrLn "What's your first name?"
firstName <- getLine
putStrLn "What's your last name?"
lastName <- getLine
let bigFirstName = map toUpper firstName
bigLastName = map toUpper lastName
putStrLn $ "hey " ++ bigFirstName ++ " " ++ bigLastName ++ ", how are you?"
===================
Questions:
1) Is there an implicit *in* before the last line above?
2) Within a do "in" the IO monad (or any other monad), can a *let* do something like this?
let x = do -- in a different monad
Michael
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