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Ghci Parse Error On Input

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An example of how this might cause trouble is as follows: Although the two lines wherebmi = ... skinny = ... Here, one coder attempted to write a function hanoi to solve the Towers of Hanoi problem, but to code it so that each tower could be named polymorphically, using, for example, It is a doubled equals sign to distinguish it from the equals sign used in let expressions. /= The not-equal-to test. As was mentioned before, GHC requires that variables and functions be defined before they are used.) The definition of g, 3 + f x, is equivalent to 3 + (f x), news

Reload to refresh your session. The system returned: (22) Invalid argument The remote host or network may be down. I think you mean to add another argument to that, most likely "input". I was making a stupid mistake; I was trying to define the variable types that were in a type signature in the actual function definition.Working code:Code: Select all-- Adds a new http://stackoverflow.com/questions/6184940/haskell-error-parse-error-on-input

Parse Error On Input Where

In this example, aside from the useless comment about indentation, it's on the right track, but it still has the latter problem of being rather cryptic. For instance: Main> let f x = 2 * x; g x = 3 + f x Main> f 5 10 Main> g 5 13 There are several small points to Haskell is more than a beginning language, however; it is also one of the most advanced and powerful. It is practically impossible to teach good programming to students who are motivated by money: As potential programmers they are mentally mutilated beyond hope of regeneration.

linking ... Haskell is a programming language. Different programs have different ideas about what a tab character should mean: a fixed number of spaces (and if so how many?) or enough space to reach the next "tab stop" Haskell Parse Error On Input Function Even if you hone your own techniques and carefully configure your tools so that you can get by with tabs, you'll cause other people who later need to edit your code

Thanks a lot! Here are some mistakes that have been observed from multiple sources. 1.1 Indentation Perhaps the first trip-up - you might understand that indentation defines where a code block starts and the Let's consider a slightly modified version of the mistake above: Main> (1 +) Top level: No instance for (Show (a -> a)) arising from use of `print' at Top level Probable By the end of this chapter, you will be able to do less trivial things, but the examples will still be quite contrived.

Russell.) 2 See also What a Monad is not Retrieved from "https://wiki.haskell.org/index.php?title=Common_Misunderstandings&oldid=60549" Category: FAQ Navigation Haskell Wiki community Recent changes Random page Tools What links here Related changes Special pages Printable Parse Error On Input Case We recommend upgrading to the latest Safari, Google Chrome, or Firefox. Top dosboot Posts: 143 Joined: Sun Jul 01, 2007 5:26 am UTC Re: Haskell - "Parse error on input" Quote Postby dosboot » Mon Jan 26, 2009 3:52 am UTC v Be Sociable, Share!

Haskell Parse Error On Input Let

An unfortunately large class of errors produces messages like this one; dealing with these messages is a more challenging aspect of learning Haskell. (Other programming systems share this problem, as well, This way. Parse Error On Input Where I was also trying it on two separate lines which works in .hs files but not in ghci. Parse Error In Pattern Haskell The theoretical difference between interpretation and compilation seems to be minimal to nonexistent given w:Partial evaluation. ↑ There are other methods of program entry (which we are ignoring for now), which

Download Haskell Try Haskell in your browser Community Guidelines Other community locations: #haskell IRC channel Planet Haskell blog aggregator Follow Haskell on Twitter Haskell mailing lists NYC Haskell Meetup videos Professional navigate to this website I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. Re: Haskell - "Parse error on input" Quote Postby Qoppa » Mon Jan 26, 2009 5:36 am UTC line:character#, not the other way around. where bmi = ... Haskell Parse Error Possibly Incorrect Indentation

Haskell layout rules specify that tab stops are 8 columns apart and that the tab character moves to the next tab stop. Logical Conjunctions[edit] Boolean Expressions and Predicates[edit] References[edit] ↑ For example: is an interpreter an interpreter if what it is really doing is just compiling an expression to machine code and executing Machine language encodes simple instructions which, when processed by the CPU, cause the computer to do useful things such as bring you to this Web page. http://blogeurope.net/parse-error/ghci-parse-error-on.php The first is the kind the function has attached to its definition; simply a name standing in for a value that is supplied when it is applied.

Prelude> add a b = a + b :2:9: parse error on input `=' noahlz commented Jun 29, 2013 Is this an issue with running in interactive mode? Haskell Parse Error On Input If permalinkembedsavegive gold[–]dave4420 5 points6 points7 points 2 years ago(10 children)And if you are using tab characters, convert them to spaces. To begin with, don't assume any preconceptions of this word related to mathematical functions; Haskell's functions are somewhat distinct.

It states that if b is true then x = y otherwise x = z.

You can google foldl' vs foldl for some better explanations. Top stone915 Posts: 42 Joined: Wed Jan 07, 2009 4:31 am UTC Re: Haskell - "Parse error on input" Quote Postby stone915 » Mon Jan 26, 2009 5:24 am UTC Berengal You should have a prompt, which says something such as Main>, in front of you. (Don't be alarmed if it says something else, such as Prelude>). Haskell Parse Error On Input Module However, I do appreciate the recommendations.

That's because they're valid Haskell; they just don't do what you expect. You may have heard of CPUs(Central Processing Units). For information, I use Ubuntu 10.4 and the version of ghc6 is 6.12.1-12 haskell share|improve this question edited Aug 19 '15 at 14:46 atc 3,33822648 asked May 31 '11 at 8:35 click site Ubuntu Logo, Ubuntu and Canonical Canonical Ltd.

look like they're aligned in your text editor (which probably uses 4-space tabs), as far as GHC is concerned what you actually have is wherebmi = ... < tab >< tab It's supposed to be deterministic; if it is possible to reach more than one state, it should return an error. The time now is 05:26 AM. Which is to say that /u/AlmostProductive is probably right and it's an indentation problem.

Do you want to help us debug the posting issues ? < is the place to report it, thanks ! Thus, g 5 becomes 3 + (2 * 5) after expanding the definitions of g and f; the expression is further evaluated to produce 13. What exact message are you getting?Code: Select allps2.hs:9:16: parse error on input `empty'
EDIT: I counted the lines, and line 16 isn't the definition of the empty function, it's this:Code: Select For instance: Main> let x = 5 Main> let y = 2 + 2 Main> let z = sqrt 9 Main> x * (y + z) 35.0 Multiple variables can be

A variable stands in for an expression. In fact, expanding nif into the function's body leaves you with exactly the above code! Browse other questions tagged haskell or ask your own question. bmiTell :: ( RealFloat a) => a -> a -> String bmiTell weight height |bmi <= skinny = "Underweight" |bmi <= 20 = "Normal" |bmi <= 25 = "Overweight" |otherwise =

When you type directly into ghci, you need to type let at the start of the line: let f x = 2 * x share|improve this answer answered May 31 '11 This is demonstrated in these examples: Main> let x = 5 Main> if x < 7 then 1 else 2 1 Main> if x <= 5 then x + 1 else Download The REPL: Using Haskell as a Calculator[edit] GHC includes a program known as GHCi, or "GHC Interactive." This program lets you type in small Haskell programs on one line, and