[Haskell] build an interpreter on top of GHCi?

Hi All, Does anybody has the experience to built an interpreter on top of GHCi? What I want is to defined a my own interpreter as a Haskell module and load it into GHCi. So this new interpreter will be running on top of GHCi which accepts syntax extension of Haskell. For example: Prelude> :l myI

[Haskell] parser for "Typing Haskell in Haskell"

Hi All, Does anybody know what parser "Typing Haskell in Haskell" use? I am tring to use the code for some type checking. But I cannot find a parser in the distribution. -W-M- @ @ | \_/ ___ Haskell mailing list [EMAIL PROTECTED] http://www.hask

constrained datatype

Hi All, Anybody knows why the following code does not work? > class Foo n > data Erk n = Foo n => Erk test.hs:53: All of the type variables in the constraint `Foo n' are already in scope (at least one must be universally quantified here) When checking the existential context of

import modules from a different directory

Hi All, Anybody has the experience of importing a module from a different directory?In my code, i need to import a module that is not in the current directory. How can I do that in GHC? -W-M- @ @ | \_/ ___ Haskell mailing list [EMAIL PROTECTED

Re: *safe* coerce, for regular and existential types

I admire the elegancy of your code which makes the changes to add new data types minimum. There is one question I want to ask: Does this technique extend to polymophic types? Let's say we have the following type: > data D a = C | D a Is it possible to index the type D a? Or there is some fundmen

dynamics on polymorphic datatype

Hi All, I am trying to perform dynamic casting on polymorphic types. Let's say I have a data type like: > data Foo a = Foo a Is there any way to use dynamics to convert a value of type Foo a to a type reprentation? I try to use the toDyn in the dynamic libray, it complains for ambigours a. Is th

polymorphic type in state of state monad

Hi All, Any one of your have the experience of defining a state of a state monad as a polymorphic type? I want to have: > type State = Term a => [a] > data M a = M (State -> IO(State,a)) GHC yields a error message "Illegal polymorphic type". How to resolve this? Thank you very much. -W-M-

overload lift function

Hi All, I have a data type defined as > data D a = D1 Int | D2 a Follow this definition, I have D2 Int,D2 Bool and D2 [D2 Int] as instances of type D. I want to write an overloaded function lift which lifts an atom type to D. It is easily done for D2 Int and D2 Bool using type classes.I can h

Re: int to float problem

Try intToFloat :: Int -> Float intToFloat n = fromInteger (toInteger n) -W-M- @ @ | \_/ On Fri, 28 Feb 2003, Mike T. Machenry wrote: > Hello, > > I am having a problem. I recently desided I wanted a bunch function to return > float instead of Int. I changed their type and wro

escape from existential quantification

I understand that existentially bound types cannot escape. For example, say we have data Foo = forall a. Foo Int a Then we cannot define a function extract (Foo i a) = a However,this limitation makes it extremly difficult to program with local quantifications.Is there any way to by pass this?