如何在 Julia 中解析多行字符串? [英] How to parse multiline string in Julia?

问题描述

如何解析更多行代码?

这是有效的:

julia> eval(parse("""print("O");print("K")"""))
OK

这不起作用:

julia> eval(parse("""print("N");
print("O")"""))
ERROR: ParseError("extra token after end of expression")
Stacktrace:
 [1] #parse#235(::Bool, ::Function, ::String) at ./parse.jl:237
 [2] parse(::String) at ./parse.jl:232

顺便说一句，如果我逐行尝试，我还有其他问题.例如:

BTW if I try line by line I have other problems. For example:

julia> parse("""for i in 1:3""")
:($(Expr(:incomplete, "incomplete: premature end of input")))

虽然:

julia> eval(parse("""for i in 1:2
println(i)
end"""))
1
2

推荐答案

parse 旨在解析单个表达式(至少文档是这么说的:鉴于此，我实际上有点惊讶您的第一个示例有效，不会引发错误...).

parse is designed to parse a single expression (at least that's what the docs say: given this I'm actually a bit surprised your first example works , without throwing an error...).

如果你想解析多个表达式，那么你可以利用以下事实:

If you want to parse mutliple expressions then you can take advantage of the fact that:

1. parse 可以接受第二个参数 start 告诉它在哪里开始解析.
2. 如果您提供此起始参数，则它会返回一个包含表达式的元组，以及表达式完成的位置.

1. parse can take a second argument start that tells it where to start parsing from.
2. If you provide this start argument then it returns a tuple containing the expression, and where the expression finished.

自己定义一个 parseall 函数.曾经有一个在基地，但我不确定是否还有.仍有测试见下文

to define a parseall function yourself. There used to be one in base but I'm not sure there is anymore. there is still in the tests see below

# modified from the julia source ./test/parse.jl
function parseall(str)
    pos = start(str)
    exs = []
    while !done(str, pos)
        ex, pos = parse(str, pos) # returns next starting point as well as expr
        ex.head == :toplevel ? append!(exs, ex.args) : push!(exs, ex) #see comments for info
    end
    if length(exs) == 0
        throw(ParseError("end of input"))
    elseif length(exs) == 1
        return exs[1]
    else
        return Expr(:block, exs...) # convert the array of expressions
                                    # back to a single expression
    end
end

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