[Haskell-cafe] "Write Yourself a Scheme in 48 Hours"

Bryan O'Sullivan bos at serpentine.com
Thu Feb 1 23:22:04 EST 2007

Shannon -jj Behrens wrote:
> I'm going through the "Write Yourself a Scheme in 48 Hours"
> <http://halogen.note.amherst.edu/~jdtang/scheme_in_48/tutorial/overview.html> 
> tutorial.  I like it a lot, but I have some concerns.  Are the
> exercises in the tutorial known to be solvable by mere mortals?

The answer seems to be "yes, iff the mortals in question have grasped 
the basics of monads, so they can fill in the gaps in the exposition."

> For instance:
> "Rewrite parseNumber using...explicit sequencing with the >>= operator"
> http://halogen.note.amherst.edu/~jdtang/scheme_in_48/tutorial/parser.html#symbols 
> There aren't any examples of using >>= previous to this question.

There's a peculiar mixture of assumptions in the article.  He treats 
monads breezily, as if they're a given; but pattern matching (much more 
basic) receives some rather more detailed exposition.  And he glosses 
over ">>", but doesn't mention the rewrite rule from "a<-x" to "x>>=\a->".

So don't beat yourself up.  The tutorial is missing a few bits and pieces.


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