Re: Parsing exercise in Forth

From	"WJ" <w_a_x_man@yahoo.com>
Newsgroups	comp.lang.forth
Subject	Re: Parsing exercise in Forth
Date	2015-12-12 17:41 +0000
Organization	A noiseless patient Spider
Message-ID	<n4hm7d$ct7$1@dont-email.me> (permalink)
References	<14a2b0f2-1137-44c5-85ca-e9d52bd7ccac@googlegroups.com> <n4f04t$b66$1@dont-email.me>

Show all headers | View raw

WJ wrote:

> krishna.myneni wrote:
> 
> > PROBLEM: Parse a string specifying the electron configuration
> > of an atom into a array of the number of electrons within each
> > subshell. Validate the string fields.
> > 
> > Example 1: The electron configuration for the lowest energy
> > state of the neutral boron atom may be specified by the
> > following string:
> > 
> > s" 1s(2) 2s(2) 2p(1)"
> > 
> > meaning there are two electrons in the "1s" (sub)shell, two
> > electrons in the "2s" subshell, and one electron in the "2p"
> > subshell. Therefore there are three array entries:
> > 
> >   Array Index  Entry
> >   ------------------
> >     0          2
> >     1          2
> >     2          1
> > 
> > Storage of the electrons numbers into the array depend on the
> > mapping between subshell and array index, as follows:
> > 
> > Index  Subshell
> >   0     "1s"
> >   1     "2s"
> >   2     "2p"
> >   3     "3s"
> >   4     "3p"
> >   5     "3d"
> >   6     "4s"
> >   7     "4p"
> >   8     "4d"
> >   9     "4f"
> > 
> > It's not necessary to go beyond these ten subshells, at this
> > point. Any subshell specifiers not in the above list should
> > return an error, indicating an invalid entry.
> > 
> > Configuration string properties:
> > 
> > 1) The order of entry of the subshells in the string shouldn't
> > matter. Any subshells that are not specified in the string
> > imply that the number of electrons in that subshell is zero,
> > and the array entries should be zeroed (usually by
> > initialization, prior to parsing the configuration string).
> > 
> > 2) Subshells with a different identifier, "spdf", in the
> > second character have a maximum number of electrons, given by
> > 
> >    s  2
> >    p  6
> >    d 10
> >    f 14
> > 
> > Therefore, a subshell entry such as "1s(3)" or "2p(7)" are
> > invalid entries, and should return an error. A negative number
> > of electrons is also not permitted, but zero is a valid count,
> > e.g. "2p(0)", although unnecessary per 1).
> > 
> > 3) Whitespace between the subshell fields is not required,
> > so a string such as s" 1s(1)2p(1)" is valid.
> > 
> > Example 2:  s" 1s(2)2s(1)3p(1)"  valid entry which results in
> > the following array elements:
> > 
> >   Index  Element
> >   ---------------
> >     0     2
> >     1     1
> >     2     0
> >     3     0
> >     4     1
> > (subsequent elements are all zero)
> > 
> > Example 3: s" 1s(2)2s(2)2d(1)"  ** invalid entry, no subshell "2d"
> > 
> > Example 4: s" 1s(2) 2s(2) 3s(4)" ** invalid entry, s subshell
> > can't have 4 electrons.
> 
> 
> Ruby:
> 
> @subshells = %w(1s 2s 2p 3s 3p 3d 4s 4p 4d 4f)
> @limits = Hash['s', 2, 'p', 6, 'd', 10, 'f', 14]
> 
> def parse_config string
>   items = string.gsub(/\s+/,"").scan( %r{([^()]+)\((.*?)\)}).
>     map{|k,v| [k, v.to_i]}
>   result = [0] * @subshells.size
>   items.each{|k,v|
>     fail "Invalid subshell: #{ k }" unless @subshells.include? k
>     fail "Too many electrons in #{ k }" if v > @limits[k[1]]
>     result[ @subshells.index(k) ] = v }
>   result
> end



Shorter:

def parse_config string
  result = [0] * 10
  string.tr(" ","").split(/[()]/).each_slice(2){|k,v|
    v = v.to_i
    i = @subshells.index k
    fail "Invalid subshell: #{k}" unless i
    fail "Too many electrons in #{k}" if v > @limits[k[1]]
    result[i] = v }
  result
end



> 
> parse_config "1s(2)2s(1)3p(1)"
>     ==>[2, 1, 0, 0, 1, 0, 0, 0, 0, 0]
> parse_config " 1s (2) 2    s ( 1  )3   p(1)  "
>     ==>[2, 1, 0, 0, 1, 0, 0, 0, 0, 0]
> 
> parse_config "1s(2)2s(2)2d(1)"
> 
>   RuntimeError: Invalid subshell: 2d
> 
> parse_config " 1s(2) 2s(2) 3s(4)"
> 
>   RuntimeError: Too many electrons in 3s



-- 
I would hesitate to describe America as a nation at all in 1997, because it is
something very different: a polyethnic federation administered by a single
ruling class....  [T]he accumulated rot in America has now reached a point
where the pillars of society itself are failing.  --- Ambrose Evans-Pritchard

Thread

Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-10 21:08 -0800
  Re: Parsing exercise in Forth Raimond Dragomir <raimond.dragomir@gmail.com> - 2015-12-11 00:09 -0800
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-11 08:59 -0800
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-11 09:02 -0800
  Re: Parsing exercise in Forth Gerard Sontag <gerardsontag@gmail.com> - 2015-12-11 02:28 -0800
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-11 09:09 -0800
  Re: Parsing exercise in Forth Pablo Hugo Reda <pabloreda@gmail.com> - 2015-12-11 06:02 -0800
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-11 09:12 -0800
  Re: Parsing exercise in Forth "WJ" <w_a_x_man@yahoo.com> - 2015-12-11 17:12 +0000
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-11 09:24 -0800
    Re: Parsing exercise in Forth "WJ" <w_a_x_man@yahoo.com> - 2015-12-12 17:41 +0000
  Re: Parsing exercise in Forth John Misciagno <jfmisciagno@gmail.com> - 2015-12-11 15:56 -0800
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-11 20:21 -0800
      Re: Parsing exercise in Forth John Misciagno <jfmisciagno@gmail.com> - 2015-12-11 22:21 -0800
  Re: Parsing exercise in Forth Julian Fondren <julian.fondren@gmail.com> - 2015-12-11 19:21 -0800
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-11 20:35 -0800
    Re: Parsing exercise in Forth "WJ" <w_a_x_man@yahoo.com> - 2015-12-12 20:08 +0000
      Re: Parsing exercise in Forth Julian Fondren <julian.fondren@gmail.com> - 2015-12-12 17:32 -0800
      Re: Parsing exercise in Forth Albert van der Horst <albert@spenarnc.xs4all.nl> - 2015-12-13 11:21 +0000
        Re: Parsing exercise in Forth Julian Fondren <julian.fondren@gmail.com> - 2015-12-13 05:14 -0800
          Re: Parsing exercise in Forth Albert van der Horst <albert@spenarnc.xs4all.nl> - 2015-12-13 17:33 +0000
  Re: Parsing exercise in Forth humptydumpty <ouatubi@gmail.com> - 2015-12-12 00:14 -0800
    Re: Parsing exercise in Forth humptydumpty <ouatubi@gmail.com> - 2015-12-12 03:48 -0800
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-12 14:52 -0800
      Re: Parsing exercise in Forth humptydumpty <ouatubi@gmail.com> - 2015-12-13 01:59 -0800
  Re: Parsing exercise in Forth franck.bensusan@gmail.com - 2015-12-12 02:53 -0800
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-12 14:58 -0800
  Re: Parsing exercise in Forth Doug Hoffman <glidedog@gmail.com> - 2015-12-12 10:33 -0500
  Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-12 14:47 -0800
  Re: Parsing exercise in Forth "WJ" <w_a_x_man@yahoo.com> - 2015-12-12 23:13 +0000
  Re: Parsing exercise in Forth humptydumpty <ouatubi@gmail.com> - 2015-12-13 10:28 -0800
  Re: Parsing exercise in Forth Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2015-12-17 17:33 +0000
    Re: Parsing exercise in Forth krishna.myneni@ccreweb.org - 2015-12-23 05:07 -0800
  Re: Parsing exercise in Forth jg <josefg@gmail.com> - 2015-12-29 15:22 -0800

csiph-web