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Example for the use of LPeg.
== Writing a parser with LPeg ==
To parser input files for the use with TeX you could either write Lua macros to convert pass the input to TeX or use LPeg to parse the files in a more simple manner.
=== First version for a sgf parser ===
The code below reads input in sgf syntax and pass the content to TeX macros.
<texcode>
\startluacode
do
thirddata = thirddata or { }
thirddata.sgf = thirddata.sgf or { }
local function command(name,x)
tex.sprint(tex.texcatcodes,string.format("\\csname sgf!%s\\endcsname{%s}",name,x))
end
local nodes = { }
function nodes.B(x) command("black" ,x) end
function nodes.W(x) command("white" ,x) end
local function action(what,data)
local a = nodes[what]
if a then
a(data)
else
print("unknown action: " .. what)
end
end
local function start()
nesting = nesting + 1
command("start",nesting)
end
local function stop()
command("stop",nesting)
nesting = nesting - 1
end
local space = lpeg.S(' \r\n')^1
local lower = lpeg.R("az")
local upper = lpeg.R("AZ")
local letter = lower + upper
local position = letter^2
local left = lpeg.P("(")
local right = lpeg.P(")")
local none = 1- (left + right)
local node = (lpeg.P(";") * lpeg.C(lpeg.S("BW")) * lpeg.P("[") * lpeg.C(position) * lpeg.P("]"))/action
local branch = lpeg.P { left/start * (lpeg.V(1) + node + space)^0 * right/stop }
local parser = (branch + node + space)^0
function thirddata.sgf.parsea(str)
nesting = 0
parser:match(str)
end
local function nest(str)
tex.sprint(tex.ctxcatcodes,string.format("\\parsesgfb{%s}",str))
end
local node = (lpeg.P(";") * lpeg.C(lpeg.S("BW")) * lpeg.P("[") * lpeg.C(position) * lpeg.P("]"))/action
local branch = lpeg.P { left * (lpeg.V(1) + (none^1/nest) + space)^0 * right }
local parser = (branch + node + space)^0
function thirddata.sgf.parseb(str)
nesting = 0
parser:match(str)
end
end
\stopluacode
</texcode>
To work with the output from the parser we need the following TeX macros.
<texcode>
\long\def\parsesgfa#1{\ctxlua{thirddata.sgf.parsea("#1")}}
\long\def\parsesgfb#1{\ctxlua{thirddata.sgf.parseb("#1")}}
\starttexdefinition sgf!start #1
\par \advance\leftskip+2em
\stoptexdefinition
\starttexdefinition sgf!stop #1
\par \advance\leftskip-2em
\stoptexdefinition
\starttexdefinition sgf!node #1
Node: #1\par
\stoptexdefinition
\starttexdefinition sgf!white #1
White: #1\par
\stoptexdefinition
\starttexdefinition sgf!black #1
Black: #1\par
\stoptexdefinition
\protect
\starttext
\parsesgfa{(;B[aa];W[bb](;B[cc](;B[dd];W[ee](;B[ff]);W[gg]));W[hh])}
\blank
\parsesgfb{(;B[aa];W[bb](;B[cc](;B[dd];W[ee](;B[ff]);W[gg]));W[hh])}
\stoptext
</texcode>
=== A extended version ===
The second version of the sgf parser is less restricted to the arguments for the commands in the input and delimits the arguments in a slightly different way than the first version.
<texcode>
\startluacode
do
thirddata = thirddata or { }
thirddata.sgf = thirddata.sgf or { }
local function command(name,x)
tex.sprint(tex.texcatcodes,string.format("\\csname sgf!%s\\endcsname{%s}",name,x))
end
local nodes = { }
function nodes.B (x) command("black" ,x) end
function nodes.W (x) command("white" ,x) end
function nodes.AW(x) command("addwhite" ,x) end
function nodes.C (x) command("comment" ,x) end
local function action(what,data)
local a = nodes[what]
if a then
for w in string.gmatch(data, "%b[]") do
a(string.sub(w,2,-2))
end
else
print("unknown action: " .. what)
end
end
local function nodecontent(str)
tex.sprint(tex.ctxcatcodes,string.format("\\csname sgf!node\\endcsname{%s}",string.sub(str,2)))
end
local space = lpeg.S(' \r\n')^1
local lcletter = lpeg.R("az")
local ucletter = lpeg.R("AZ")
local letter = lcletter + ucletter
local propindent = ucletter^1
local property = lpeg.C(propindent) * lpeg.C{ (lpeg.P("[") * (1 - lpeg.S"[]")^0 * lpeg.P("]"))^1} / action
local function nest(str)
tex.sprint(tex.ctxcatcodes,string.format("\\parsesgf{%s}",string.sub(str,2,-2)))
end
local node = lpeg.P{ ";" * (propindent * (lpeg.P("[") * (1 - lpeg.S"[]")^0 * lpeg.P("]"))^1)^1} / nodecontent
local branch = lpeg.P{ "(" * ((1 - lpeg.S"()") + lpeg.V(1))^0 * ")" } / nest
local parser = (branch + node + property + space)^0
function thirddata.sgf.parse(str)
parser:match(str)
end
end
\stopluacode
</texcode>
The TeX code for the second version is nearly the same as in the first draft, this was the goal for both version because it is more important to keep the interface in TeX and make the modifications in low level TeX or Lua code.
<texcode>
\def\sgfflush#1{\ctxlua{thirddata.sgf.parse("#1")}}
\starttexdefinition parsesgf #1
\par \advance\leftskip+2em
\sgfflush{#1}
\par \advance\leftskip-2em
\stoptexdefinition
\starttexdefinition sgf!node #1
\par \sgfflush{#1}
\stoptexdefinition
\starttexdefinition sgf!white #1
White: #1\quad
\stoptexdefinition
\starttexdefinition sgf!black #1
Black: #1\quad
\stoptexdefinition
\starttexdefinition sgf!addwhite #1
Add White: #1\quad
\stoptexdefinition
\starttexdefinition sgf!comment #1
Comment: #1\quad
\stoptexdefinition
\protect
\starttext
\parsesgf{(;C[First move in game 123]B[aa]AW[aa];W[bb](;B[cc](;B[dd];W[ee][ff](;B[ff]);W[gg]));W[hh])}
\stoptext
</texcode>
== External Links ==
* http://www.inf.puc-rio.br/~roberto/lpeg.html
To parser input files for the use with TeX you could either write Lua macros to convert pass the input to TeX or use LPeg to parse the files in a more simple manner.
=== First version for a sgf parser ===
The code below reads input in sgf syntax and pass the content to TeX macros.
<texcode>
\startluacode
do
thirddata = thirddata or { }
thirddata.sgf = thirddata.sgf or { }
local function command(name,x)
tex.sprint(tex.texcatcodes,string.format("\\csname sgf!%s\\endcsname{%s}",name,x))
end
local nodes = { }
function nodes.B(x) command("black" ,x) end
function nodes.W(x) command("white" ,x) end
local function action(what,data)
local a = nodes[what]
if a then
a(data)
else
print("unknown action: " .. what)
end
end
local function start()
nesting = nesting + 1
command("start",nesting)
end
local function stop()
command("stop",nesting)
nesting = nesting - 1
end
local space = lpeg.S(' \r\n')^1
local lower = lpeg.R("az")
local upper = lpeg.R("AZ")
local letter = lower + upper
local position = letter^2
local left = lpeg.P("(")
local right = lpeg.P(")")
local none = 1- (left + right)
local node = (lpeg.P(";") * lpeg.C(lpeg.S("BW")) * lpeg.P("[") * lpeg.C(position) * lpeg.P("]"))/action
local branch = lpeg.P { left/start * (lpeg.V(1) + node + space)^0 * right/stop }
local parser = (branch + node + space)^0
function thirddata.sgf.parsea(str)
nesting = 0
parser:match(str)
end
local function nest(str)
tex.sprint(tex.ctxcatcodes,string.format("\\parsesgfb{%s}",str))
end
local node = (lpeg.P(";") * lpeg.C(lpeg.S("BW")) * lpeg.P("[") * lpeg.C(position) * lpeg.P("]"))/action
local branch = lpeg.P { left * (lpeg.V(1) + (none^1/nest) + space)^0 * right }
local parser = (branch + node + space)^0
function thirddata.sgf.parseb(str)
nesting = 0
parser:match(str)
end
end
\stopluacode
</texcode>
To work with the output from the parser we need the following TeX macros.
<texcode>
\long\def\parsesgfa#1{\ctxlua{thirddata.sgf.parsea("#1")}}
\long\def\parsesgfb#1{\ctxlua{thirddata.sgf.parseb("#1")}}
\starttexdefinition sgf!start #1
\par \advance\leftskip+2em
\stoptexdefinition
\starttexdefinition sgf!stop #1
\par \advance\leftskip-2em
\stoptexdefinition
\starttexdefinition sgf!node #1
Node: #1\par
\stoptexdefinition
\starttexdefinition sgf!white #1
White: #1\par
\stoptexdefinition
\starttexdefinition sgf!black #1
Black: #1\par
\stoptexdefinition
\protect
\starttext
\parsesgfa{(;B[aa];W[bb](;B[cc](;B[dd];W[ee](;B[ff]);W[gg]));W[hh])}
\blank
\parsesgfb{(;B[aa];W[bb](;B[cc](;B[dd];W[ee](;B[ff]);W[gg]));W[hh])}
\stoptext
</texcode>
=== A extended version ===
The second version of the sgf parser is less restricted to the arguments for the commands in the input and delimits the arguments in a slightly different way than the first version.
<texcode>
\startluacode
do
thirddata = thirddata or { }
thirddata.sgf = thirddata.sgf or { }
local function command(name,x)
tex.sprint(tex.texcatcodes,string.format("\\csname sgf!%s\\endcsname{%s}",name,x))
end
local nodes = { }
function nodes.B (x) command("black" ,x) end
function nodes.W (x) command("white" ,x) end
function nodes.AW(x) command("addwhite" ,x) end
function nodes.C (x) command("comment" ,x) end
local function action(what,data)
local a = nodes[what]
if a then
for w in string.gmatch(data, "%b[]") do
a(string.sub(w,2,-2))
end
else
print("unknown action: " .. what)
end
end
local function nodecontent(str)
tex.sprint(tex.ctxcatcodes,string.format("\\csname sgf!node\\endcsname{%s}",string.sub(str,2)))
end
local space = lpeg.S(' \r\n')^1
local lcletter = lpeg.R("az")
local ucletter = lpeg.R("AZ")
local letter = lcletter + ucletter
local propindent = ucletter^1
local property = lpeg.C(propindent) * lpeg.C{ (lpeg.P("[") * (1 - lpeg.S"[]")^0 * lpeg.P("]"))^1} / action
local function nest(str)
tex.sprint(tex.ctxcatcodes,string.format("\\parsesgf{%s}",string.sub(str,2,-2)))
end
local node = lpeg.P{ ";" * (propindent * (lpeg.P("[") * (1 - lpeg.S"[]")^0 * lpeg.P("]"))^1)^1} / nodecontent
local branch = lpeg.P{ "(" * ((1 - lpeg.S"()") + lpeg.V(1))^0 * ")" } / nest
local parser = (branch + node + property + space)^0
function thirddata.sgf.parse(str)
parser:match(str)
end
end
\stopluacode
</texcode>
The TeX code for the second version is nearly the same as in the first draft, this was the goal for both version because it is more important to keep the interface in TeX and make the modifications in low level TeX or Lua code.
<texcode>
\def\sgfflush#1{\ctxlua{thirddata.sgf.parse("#1")}}
\starttexdefinition parsesgf #1
\par \advance\leftskip+2em
\sgfflush{#1}
\par \advance\leftskip-2em
\stoptexdefinition
\starttexdefinition sgf!node #1
\par \sgfflush{#1}
\stoptexdefinition
\starttexdefinition sgf!white #1
White: #1\quad
\stoptexdefinition
\starttexdefinition sgf!black #1
Black: #1\quad
\stoptexdefinition
\starttexdefinition sgf!addwhite #1
Add White: #1\quad
\stoptexdefinition
\starttexdefinition sgf!comment #1
Comment: #1\quad
\stoptexdefinition
\protect
\starttext
\parsesgf{(;C[First move in game 123]B[aa]AW[aa];W[bb](;B[cc](;B[dd];W[ee][ff](;B[ff]);W[gg]));W[hh])}
\stoptext
</texcode>
== External Links ==
* http://www.inf.puc-rio.br/~roberto/lpeg.html
