Start with a value.

01 / Values

Change what’s there.

A record holds a few labeled values. This one has a greeting and a count. Each value has its own little editor.

1. 1Not yet completed: Click inside Hello, world! and change the greeting.
2. 2Not yet completed: Change the count from 3 to another number.

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The braces and labels stay in place. You’re editing a value, not a line of source text.

02 / Lists

Make room for something new.

A list keeps values in order. You can edit its items, or change the list itself.

1. 1Not yet completed: Click a comma to open a space between two items.
2. 2Not yet completed: Type "peaches", including the quotes, then press Enter to insert it.
3. 3Not yet completed: Click a square bracket to select the whole list.
4. 4Not yet completed: Click inside an item and erase its text with Backspace. One more Backspace removes the empty item from the list.
5. 5Not yet completed: Press Ctrl + Z to undo the removal and bring the item back.

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You don’t have to balance brackets or repair commas. The list is already a list.

03 / Cells

One value, in two places.

These aren’t two separate copies of 7. Both pairs of parentheses refer to the same cell. A cell holds a value; changing it changes what you see everywhere it’s referenced.

1. 1Not yet completed: Change either 7. Watch the other one change too.
2. 2Not yet completed: Click a comma and type ( to create a new cell. Click the empty box inside it, type 11, then press Enter.
3. 3Not yet completed: Click another comma to open a space. Hold Ctrl and click a parenthesis around your new cell—not the number—to put another reference there.
4. 4Not yet completed: Change either 11. Its new partner changes too; the original pair stays separate.

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Cells can hold lists, records, or any other value—not just numbers. The parentheses select the reference; the inside edits its contents.

04 / Grap

Let a value do some work.

Grap is a programming language built from these same structures. Here, each expression before an arrow is evaluated; its result appears after the arrow. * means multiply.

The three parenthesized 3s refer to one cell: on its own, in an addition, and in a multiplication.

1. 1Not yet completed: Change the 2 after + to 4. The sum becomes 7; the multiplication stays at 6.
2. 2Not yet completed: Change any parenthesized 3 to 5. All three references update. After the first step, the results become 9 and 10.

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Results are read-only; change the numbers in the expressions to change them.

05 / Functions

One recipe, different inputs.

The first line defines scale: it takes a parameter called x and multiplies it by 2. The next two lines call that function with different numbers and show their results.

Unlike the shared number in the previous example, x gets its value separately for each call.

1. 1Not yet completed: Change the first call’s 3 to 4. Its result becomes 8; the other stays at 10.
2. 2Not yet completed: In the function definition, change the multiplier 2 to 3. After the first step, both results update to 12 and 15.
3. 3Not yet completed: Click x inside the definition’s parameter list and rename it to amount. Its uses and the call labels change too; the results stay the same.

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Names make references readable. Renaming a parameter doesn’t break its connections: they use the cell’s identity, not its spelling.