我正在努力让我的头脑围绕着LPEG.我已经设法制作了一个符合我想要的语法,但是我一直在反对这个语法并且没有走远.我们的想法是解析一个简化形式的TeX文档.我想将文档分成:
\begin{cmd}和\end{cmd}成对的.\foo{bar}或者可以是裸的:\foo.\command[color=green,background=blue]{content}.我还想跟踪行号信息以便进行错误处理.这是我到目前为止所拥有的:
lpeg = require("lpeg")
lpeg.locale(lpeg)
-- Assume a lot of "X = lpeg.X" here.
-- Line number handling from http://lua-users.org/lists/lua-l/2011-05/msg00607.html
-- with additional print statements to check they are working.
local newline = P"\r"^-1 * "\n" / function (a) print("New"); end
local incrementline = Cg( Cb"linenum" )/ function ( a ) print("NL"); return a + 1 end , "linenum"
local setup = Cg ( Cc ( 1) , "linenum" )
nl = newline * incrementline
space = nl + lpeg.space
-- Taken from "Name-value lists" in http://www.inf.puc-rio.br/~roberto/lpeg/
local identifier = (R("AZ") + R("az") + P("_") + R("09"))^1
local sep = lpeg.S(",;") * space^0
local value = (1-lpeg.S(",;]"))^1
local pair = lpeg.Cg(C(identifier) * space ^0 * "=" * space ^0 * C(value)) * sep^-1
local list = lpeg.Cf(lpeg.Ct("") * pair^0, rawset)
local parameters = (P("[") * list * P("]")) ^-1
-- And the rest is mine
anything = C( (space^1 + (1-lpeg.S("\\{}")) )^1) * Cb("linenum") / function (a,b) return { text = a, line = b } end
begin_environment = P("\\begin") * Ct(parameters) * P("{") * Cg(identifier, "environment") * Cb("environment") * P("}") / function (a,b) return { params = a[1], environment = b } end
end_environment = P("\\end{") * Cg(identifier) * P("}")
texlike = lpeg.P{
"document";
document = setup * V("stuff") * -1,
stuff = Cg(V"environment" + anything + V"bracketed_stuff" + V"command_with" + V"command_without")^0,
bracketed_stuff = P"{" * V"stuff" * P"}" / function (a) return a end,
command_with =((P("\\") * Cg(identifier) * Ct(parameters) * Ct(V"bracketed_stuff"))-P("\\end{")) / function (i,p,n) return { command = i, parameters = p, nodes = n } end,
command_without = (( P("\\") * Cg(identifier) * Ct(parameters) )-P("\\end{")) / function (i,p) return { command = i, parameters = p } end,
environment = Cg(begin_environment * Ct(V("stuff")) * end_environment) / function (b,stuff, e) return { b = b, stuff = stuff, e = e} end
}
它几乎可以工作!
> texlike:match("\\foo[one=two]thing\\bar")
{
command = "foo",
parameters = {
{
one = "two",
},
},
}
{
line = 1,
text = "thing",
}
{
command = "bar",
parameters = {
},
}
但!首先,我无法让行号处理部分工作.内部函数incrementline永远不会被触发.
我也不太工作了捕获如何嵌套的信息传递给处理函数(这就是为什么我有散在的Cg,C和Ct半随机在语法).这意味着只有一个项目从以下内容返回command_with:
> texlike:match("\\foo{text \\command moretext}")
{
command = "foo",
nodes = {
{
line = 1,
text = "text ",
},
},
parameters = {
},
}
我也希望能够检查环境的开始和结束是否匹配,但是当我尝试这样做的时候,"开始"的后面引用在我"结束"时不在范围内.我不知道从哪里开始.
迟到的答案,但希望如果您仍在寻找解决方案或想知道问题是什么,它会提供一些见解.
你的语法有几个问题,其中一些可能很难发现.
此处的行增量看起来不正确:
local incrementline = Cg( Cb"linenum" ) /
function ( a ) print("NL"); return a + 1 end,
"linenum"
看起来您打算创建一个命名的捕获组而不是匿名组.后捕获linenum基本上像变量一样使用.问题是因为这是在匿名捕获中,linenum不会正确更新 - function(a)在调用时总是会收到1.你需要将结束移动到最后),所以"linenum"包括:
local incrementline = Cg( Cb"linenum" /
function ( a ) print("NL"); return a + 1 end,
"linenum")
用于捕获的相关LPeg文档Cg.
第二个问题是你的anything非终端规则:
anything = C( (space^1 + (1-lpeg.S("\\{}")) )^1) * Cb("linenum") ...
这里有几件事需要注意.首先,一个命名的 Cg捕获(从incrementline规则一旦它被修复)除非它在一个表中或你反向它,否则不会产生任何东西.第二个主要的是它有一个像变量这样的特殊范围.更确切地说,一旦你在外部捕获中关闭它,它的范围就会结束 - 就像你在这里所做的那样:
C( (space^1 + (...) )^1)
这意味着当你引用它的后备时* Cb("linenum"),那已经太晚了 - linenum你真的想要已经关闭了它的范围.
我总是发现LPeg的re语法更容易理解,所以我用它重写了语法:
local grammar_cb =
{
fold = pairfold,
resetlinenum = resetlinenum,
incrementlinenum = incrementlinenum, getlinenum = getlinenum,
error = error
}
local texlike_grammar = re.compile(
[[
document <- '' -> resetlinenum {| docpiece* |} !.
docpiece <- {| envcmd |} / {| cmd |} / multiline
beginslash <- cmdslash 'begin'
endslash <- cmdslash 'end'
envcmd <- beginslash paramblock? {:beginenv: envblock :} (!endslash docpiece)*
endslash openbrace {:endenv: =beginenv :} closebrace / &beginslash {} -> error .
envblock <- openbrace key closebrace
cmd <- cmdslash {:command: identifier :} (paramblock? cmdblock)?
cmdblock <- openbrace {:nodes: {| docpiece* |} :} closebrace
paramblock <- opensq ( {:parameters: {| parampairs |} -> fold :} / whitesp) closesq
parampairs <- parampair (sep parampair)*
parampair <- key assign value
key <- whitesp { identifier }
value <- whitesp { [^],;%s]+ }
multiline <- (nl? text)+
text <- {| {:text: (!cmd !closebrace !%nl [_%w%p%s])+ :} {:line: '' -> getlinenum :} |}
identifier <- [_%w]+
cmdslash <- whitesp '\'
assign <- whitesp '='
sep <- whitesp ','
openbrace <- whitesp '{'
closebrace <- whitesp '}'
opensq <- whitesp '['
closesq <- whitesp ']'
nl <- {%nl+} -> incrementlinenum
whitesp <- (nl / %s)*
]], grammar_cb)
回调函数直接定义为:
local function pairfold(...)
local t, kv = {}, ...
if #kv % 2 == 1 then return ... end
for i = #kv, 2, -2 do
t[ kv[i - 1] ] = kv[i]
end
return t
end
local incrementlinenum, getlinenum, resetlinenum do
local line = 1
function incrementlinenum(nl)
assert(not nl:match "%S")
line = line + #nl
end
function getlinenum() return line end
function resetlinenum() line = 1 end
end
使用具有多行的非平凡的tex-like str测试语法:
local test1 = [[\foo{text \bar[color = red, background = black]{
moretext \baz{
even
more text} }
this time skipping multiple
lines even, such wow!}]]
以lua-table格式生成以下AST:
{
command = "foo",
nodes = {
{
text = "text",
line = 1
},
{
parameters = {
color = "red",
background = "black"
},
command = "bar",
nodes = {
{
text = " moretext",
line = 2
},
{
command = "baz",
nodes = {
{
text = "even ",
line = 3
},
{
text = "more text",
line = 4
}
}
}
}
},
{
text = "this time skipping multiple",
line = 7
},
{
text = "lines even, such wow!",
line = 9
}
}
}
对开始/结束环境进行第二次测试:
local test2 = [[\begin[p1
=apple,
p2=blue]{scope} scope foobar
\end{scope} global foobar]]
这似乎给出了你正在寻找的东西:
{
{
{
text = " scope foobar",
line = 3
},
parameters = {
p1 = "apple",
p2 = "blue"
},
beginenv = "scope",
endenv = "scope"
},
{
text = " global foobar",
line = 4
}
}