vistuleB/vxml_parser

vxml_parser

Intro

VXML looks like this (text & tag nodes only; tag nodes can have attributes):

<> vxmlSample
    attr1 mom
    attr2 dad
    <>
        "this is a text child"
        "with two lines"
    <> html
        <> header
            charset utf-8
        <> body
            <> div
                <>
                    "some text"
                    "more text"
        <> goda
            <> child1
            <> child2
            <>
                "hello I am child3, but the first text child"
            <> child4
<> "yello"

Development

gleam run   # Run the project

What's there

Here is a dumbed-down version of the VXML type:

pub type VXML {
  V(
    tag: String,
    attributes: List(#(String, String)),
    children: List(VXML),
  )
  T(
    contents: List(String)
  )
}

This is gleam syntax for "a VXML is either a V or a T, where V has these fields and T has those fields".

In reality the type is a little more complex every parsed line carries a Blame:

pub type Blame {
  Blame(filename: String, line_no: Int, comments: List(String))
}

The parser doesn't really care about Blame but they are littered everywhere. (They will help us track source across multiple desugarings etc.)

So in fact, the true collection of types, with Blame everywhere, is like so:

pub type Blame {
  Blame(filename: String, line_no: Int, comments: List(String))
}

pub type BlamedContent {
  BlamedContent(blame: Blame, content: String)
}

pub type BlamedAttribute {
  BlamedAttribute(blame: Blame, key: String, value: String)
}

pub type VXML {
  V(
    blame: Blame,
    tag: String,
    attributes: List(BlamedAttribute),
    children: List(VXML),
  )
  T(blame: Blame, contents: List(BlamedContent))
}

We also have a parser error type:

pub type VXMLParseError {
  VXMLParseErrorEmptyTag(Blame)
  VXMLParseErrorIllegalTagCharacter(Blame, String, String)
  VXMLParseErrorIllegalAttributeKeyCharacter(Blame, String, String)
  VXMLParseErrorIndentationTooLarge(Blame, String)
  VXMLParseErrorIndentationNotMultipleOfFour(Blame, String)
  VXMLParseErrorTextMissing(Blame)
  VXMLParseErrorTextOutOfPlace(Blame, String)
  VXMLParseErrorCaretExpected(Blame, String)
  VXMLParseErrorConsecutiveTextNodes(Blame)
}

Homework

You can try gleam run and modifying src/sample.vxml to see what happens when errors are introduced to the file.