Re: Reading in floats from strings???

My quick&dirty way to parse numeric values in string format is Scanf, using
formats of the kind " %d" (for integers) and " %f" (for floats), with the
space having the meaning of "ignore any space before".

It is easier to do on the standard input directly:

  let read_next_float () = Scanf.scanf " %f" (fun x -> x)

  let () =
    let x = read_next_float () in
    let y = read_next_float () in
    print_float (x +. y)

if your input comes from a string, you have to convert it into a scanning
buffer first:
  http://caml.inria.fr/pub/docs/manual-ocaml/libref/Scanf.html
  http://caml.inria.fr/pub/docs/manual-ocaml/libref/Scanf.Scanning.html

  let read_next_float input = Scanf.bscanf input " %f" (fun x -> x)

  let sum_of_string str =
    let input = Scanf.Scanning.from_string str in
    let x = read_next_float input in
    let y = read_next_float input in
    (x +. y)

Please be aware, however, that Scanf is best used for programs where you
control the input. It does not perform much input validation, and if you
want to provide a convenient user interface to your user and be robust to
formatting errors, you should use a more robust parsing strategy. I have
never personally been in the situation where regexp parsing felt like the
right compromise between expressivity and convenience, I tend to move to
full lexer+parser stacks directly (which are easy to use in OCaml, see
[sedlex] + [menhir]), but that's a question of habits I guess.

 sedlex: https://github.com/alainfrisch/sedlex
 menhir: http://gallium.inria.fr/~fpottier/menhir/
 compiling a project using both:
http://stackoverflow.com/questions/30853159/using-menhir-with-sedlex

On Wed, Jan 27, 2016 at 10:29 AM, Douglas Lewit [email protected]
[ocaml_beginners] <[email protected]> wrote:

>
>
> Hi everyone,
>
> I am new to this list, so I thought I would introduce myself.  Also, I
> have a question about how to read in data of the form "11.3  12.9".
> Obviously a string, but I need to extract the floats contained in the
> string.  I know how to do that in Java and also in Python, but for me Ocaml
> is still pretty much a foreign language.  I appreciate any guidance you can
> offer.
>
> Anyhow, I've got a master's in math from a small state university in
> Chicago, Illinois.  I'm currently working on a second master's in CS at the
> same university.  My work experience is mostly in teaching, although I've
> also done some retail management.  I used to be a high school math teacher
> ( mostly Catholic high schools, but also have some experience in the public
> school system ) and currently I teach part-time at Oakton Community College
> ( near Chicago ).  I'm interested in leaving education within the next
> couple of years to find a new career in the software industry.  My age
> could be a factor that works to my disadvantage, since most of the people
> that I personally know in various startup companies are quite young.  (
> I've been to some Python and Ruby meetups in the Chicago area, and I get
> the distinct impression that the vast majority of attendees are under the
> age of 35. )
>
> Ocaml is appealing to me for a couple of reasons.  Well first off, how can
> I resist a book that has a picture of a lovable camel on its front cover!!!
>   ;-)   But on a more serious note, I like Ocaml because it really forces
> the programmer to get over his fear or hatred of recursion.  I think
> recursion is sort of optional in many other languages, and in fact some
> programmers really hate it because it does require a different way of
> thinking about problems.  But in Ocaml recursion is not optional.  So for
> me it's a really good exercise in thinking recursively about various
> problems.  Although sometimes I think Ocaml goes a little too far with its
> emphasis on recursion.  I mean.... there are times when a nice little for
> loop or while loop would do the job with far greater simplicity!
>
> From the reading I have done on the web it appears that Ocaml is a big hit
> with Jane Street, a very large financial trading company with offices in
> NYC, London and Hong Kong.  Outside of Jane Street, where is Ocaml used?
>
> Take care and thanks for reading my intro message.
>
> Best,
>
> Douglas Lewit
>
> P.S.  Is there any connection between Ocaml and Wolfram Mathematica?  Both
> begin and end comments with (* and *), respectively, and both emphasize the
> functional approach to programming.  I'm a big fan of Mathematica, and
> often incorporate it into math classes that I teach.  I'm just wondering if
> there's a connection between the two software projects.  Thanks.
>
>
>
> 
>