shopify_draft_proxy/graphql/lexer

Mirrors graphql-js language/lexer.ts.

The lexer walks a Source.body codepoint-by-codepoint and produces a stream of Token values. The Gleam port differs from graphql-js in three intentional ways:

1. Lexer state is immutable. next_token returns the next token plus a fresh Lexer to thread through the parser, instead of mutating this.line / this.token like graphql-js does.
2. Errors are returned as Result(_, LexError) rather than thrown.
3. Position semantics use Unicode code points, not UTF-16 code units. For ASCII Shopify GraphQL queries (which is all the proxy parses) this is identical to graphql-js; supplementary-plane characters would diverge by one position per surrogate pair.

Block strings ("""...""") are intentionally not implemented in the spike — operation documents under config/parity-requests/** do not contain them. A clear error is raised if one is encountered.

pub type LexError {
  LexError(
    message: String,
    position: Int,
    line: Int,
    column: Int,
  )
}

pub type Lexer {
  Lexer(
    source: source.Source,
    remaining: List(Int),
    position: Int,
    line: Int,
    line_start: Int,
  )
}

pub fn lex(
  source: source.Source,
) -> Result(List(token.Token), LexError)

pub fn new(source: source.Source) -> Lexer

pub fn next_token(
  lexer: Lexer,
) -> Result(#(token.Token, Lexer), LexError)