[NTG-context] the other blog (chemical stuff)

6 Mar 2009

      Hi aditya,

some comments on the other bog item ... (others may wikify it)

you can do a quick and dirty solution as well (tested in mkiv):

\def\MoleculeC#1{$\enablesupersub\tf#1$}

now, concerning the lua solution, it looks pretty clean and ok, but 
there is some room for improvement ... the following version supports 
nested braces and numbers (we can let this evolve in a proper chemical
subsystem if needed since eventually i will replace ppchtex anyway)

\startluacode
local molecule = { }

local format, sprint = string.format, tex.sprint

function commands.justtext(one)
     sprint(tex.ctxcatcodes,one)
end

function commands.low(str)
     sprint(tex.ctxcatcodes,format("\\low{%s}",str))
end

function commands.high(str)
     sprint(tex.ctxcatcodes,format("\\high{%s}",str))
end

function commands.lowhigh(one,two)
     sprint(tex.ctxcatcodes,format("\\lohi{%s}{%s}",one,two))
end

function commands.highlow(one,two)
     sprint(tex.ctxcatcodes,format("\\hilo{%s}{%s}",one,two))
end

local lowercase   = lpeg.R("az")
local uppercase   = lpeg.R("AZ")

local plus        = lpeg.P("+")
local minus       = lpeg.P("-")
local digit       = lpeg.R("09")
local sign        = plus + minus
local cardinal    = digit^1
local integer     = sign^0 * cardinal

local leftbrace   = lpeg.P("{")
local rightbrace  = lpeg.P("}")
local nobrace     = 1 - (leftbrace + rightbrace)
local nested      = lpeg.P { leftbrace * (nobrace + lpeg.V(1))^0 * 
rightbrace }
local any         = lpeg.P(1)

local subscript   = lpeg.P("_")
local superscript = lpeg.P("^")

local content     = lpeg.C(nested + integer + any)

-- could be made more efficient

local lowhigh  = subscript   * content * superscript * content / 
commands.lowhigh
local highlow  = superscript * content * subscript   * content / 
commands.highlow
local low      = subscript   * content                         / 
commands.low
local high     = superscript * content                         / 
commands.high
local justtext = lpeg.C((1 - somescript)^1)                    / 
commands.justtext

local parser = (sometext + lowhigh + highlow + low + high)^0

function commands.molecule(string)
     parser:match(string)
end
\stopluacode

\def\molecule#1{\ctxlua{commands.molecule("#1")}}

\molecule{H_2SO_4^-2}
\molecule{H_2SO_4^{-2}}
\molecule{H_2SO_4^{-2{x}}}

Hans

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