JSONYAMLJSON SchemaIntermediate~4h

JSON & YAML

Say what the parser returns

These two formats look like the easiest thing in computing, and both are parsed by machines that disagree with the person reading them. Here is the whole of it, exactly: which documents are legal, what every value becomes, where the two YAML versions differ, and how to decide a document against a schema.

Start this project See the modules

Modules: 5
Drills: 12
Build steps: 2
Time: ~4h

Walk out able to

Hand someone a document and tell them what their parser will return — the structure, the type of every scalar, and whether it is accepted at all.

Prediction, not familiarity.

What you will be able to predict

Legal, and what it became

The six rules that refuse a document, and what it becomes.

Numbers and round trips

Where integers stop being exact, and what round trips lose.

Escapes, quotes, code points

What a string holds, and which quotes process escapes.

YAML surprises, and schemas

Typing by version, indentation as structure, and a verdict.

The pitch

What you practise, and what you leave with

A JSON Schema you write for a real configuration, which accepts it and refuses six corruptions of it — each on a different keyword.

You will practise

Legal documents, and the rule that refused one
Numbers, round trips and parsed string lengths
YAML typing, quoting, blocks and indentation
Schema verdicts, and the keyword behind each

Afterwards you can

Name the rule that refused a document
Say what a YAML scalar is, and under which version
Count what a parsed string actually holds
Decide a document against a schema exactly

Modules

5 modules, 23 items

Lessons explain one idea. Drills repeat it until it sticks. Build steps make something that exists afterwards.

1
What the parser accepts
~39 min
Say whether a document parses, name the rule that refused it, and read the value out.
- LessonWhy these two formats together5 min
- LessonPredict what the parser refuses10 min
- LessonSee what a repeated key does4 min
- DrillName the rule that refused it10 min
- DrillWalk a document to a value10 min
2
What the value is
~32 min
Predict the number that comes back, and name what a round trip quietly removed.
- DrillRead the integer back10 min
- LessonFind where the number changes12 min
- DrillSay what the round trip dropped10 min
3
Escapes, quotes and code points
~42 min
Count what a parsed string holds, and pick a quoting style knowing what it processes.
- LessonNine escapes, and nothing else5 min
- LessonCount what the string really holds8 min
- DrillMeasure the parsed string10 min
- DrillSpot the escape that is refused9 min
- DrillSay what each quoting style holds10 min
4
Where YAML disagrees with you
~48 min
Type any scalar the way a named parser will, and read an indented block exactly.
- LessonMeet the value you did not write11 min
- LessonReuse a block with an anchor6 min
- DrillType the scalar as the parser will11 min
- DrillRead a block scalar exactly10 min
- DrillRead the indentation as structure10 min
5
Decide it against a schema
~59 min
Give a verdict, name the keyword behind it, then write the schema yourself.
- LessonRead a schema as a claim13 min
- DrillGive the verdict, name the keyword11 min
- DrillCount what survives the schema10 min
- Build stepWrite the schema that accepts it12 min
- Build stepBreak it seven ways, and count13 min