Lesson 06 · Scanning a basic string

Scanning a basic string

Strings are where JSON stops being pure punctuation and starts carrying data. Today you scan a quoted string with no escapes into a token that holds its decoded text.

The goal

Scan a double-quoted run of plain characters into a String token carrying its contents.

Start here - the target

TO DO

Scenario: Reading a plain quoted string

Giventhe input consisting of the three characters quote, a, b, c, quote

Whenit is scanned

Thenit yields a String token whose value is abc, followed by EOF

Andan empty quoted string yields a String token whose value is the empty string

Background

A JSON string is a run of characters wrapped in double quotes. The opening quote tells the scanner “a string starts here”; it then reads forward until the closing quote, and the bytes in between are the string’s value. The quotes themselves are delimiters, not part of the value, so "abc" carries abc and "" carries the empty string.

Today deliberately handles only the simple case: no backslash escapes, and a closing quote that is really there. That keeps the lesson to one idea - delimit and capture the contents - and gives you a Str field on the token to hold the decoded text. The next lessons layer in escapes, Unicode, and the error when the closing quote never comes. Assume a well-formed simple string for now.

Make it work

// add String to Kind; give Token a Str field for the decoded value
// on seeing '"', consume characters until the closing '"'
// for now assume no backslashes and a closing quote is present
//   start := i+1; scan to next '"'; Str = input[start:i]

CheckpointDONE

The scanner reads plain double-quoted strings into String tokens. Commit and stop here.