▼ |  | Unstable: May Change Without Warning

1 | Guidelines for Developing unstable Libraries
2 | Automata: Compiling State Machines
3 | Bytes
4 | Contracts
5 | Contracts for Macro Subexpressions
6 | Debugging
7 | Definitions
8 | Errors
9 | Futures
10 | Functions
11 | Hash Tables
12 | Interface-Oriented Programming for Classes
13 | Lazy Require
14 | Lists
15 | Logging
16 | Macro Testing
17 | Mark Parameters
18 | Match
19 | Open place expressions
20 | Options
21 | Parameter Groups
22 | Pretty-Printing
23 | Re-Contracting Identifiers
24 | Sandbox
25 | Sequences
26 | Strings
27 | Structs
28 | Struct Printing
29 | Syntax
30 | Temporal Contracts: Explicit Contract Monitors
31 | Unix Domain Sockets
32 | 2D Syntax

► | 32 | 2D Syntax

32.1 | Editing 2D
32.2 | 2D Cond
32.3 | 2D Match
32.4 | 2D Tabular

On this page:

32.1`` Editing 2D
32.2`` 2D Cond
2dcond
32.3`` 2D Match
2dmatch
32.4`` 2D Tabular
2dmatch

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### 32`` 2D Syntax

#lang unstable/2d | package: base

The unstable/2d language installs #2d reader support in the readtable, and then chains to the reader of another language that is specified immediately after unstable/2d.

The #2d syntax extension adds the ability use a two-dimensional grid syntax. That is, you can draw an ASCII-art grid and then treat that as an expression. For example, here is a simple equality function that operates on pairs and numbers, written using a #2d conditional expression:

> #lang unstable/2d racket
> (require unstable/2d/cond)
> (define (same? a b)
> #2dcond
> ╔═════════════╦═══════════════════════╦═════════════╗
> ║ ║ (pair? a) ║ (number? a) ║
> ╠═════════════╬═══════════════════════╬═════════════╣
> ║ (pair? b) ║ (and (same? (car a) ║ #f ║
> ║ ║ (car b)) ║ ║
> ║ ║ (same? (cdr a) ║ ║
> ║ ║ (cdr b))) ║ ║
> ╠═════════════╬═══════════════════════╬═════════════╣
> ║ (number? b) ║ #f ║ (= a b) ║
> ╚═════════════╩═══════════════════════╩═════════════╝)

This notation works in two stages: reading, and parsing (just as in Racket in general). The reading stage converts anything that begins with #2d into a parenthesized expression (possibly signaling errors if the ═ and ║ and ╬ characters do not line up in the right places).

Since the first line contains #2dcond, the reader will produce a sequence whose first position is the identifier 2dcond.

That macro will take over and then expand into ordinary conditional expressions, in this case figuring out whether or not the inputs are pairs or numbers and evaluating the code in the appropriate cell.

At the reader level, the syntax #2d notation checks the number of columns in the first row and uses that as a guide for where subsequent rows may appear. Once that first row is set, it serves as a guide to where the columns may appear in subsequent rows, although following columns may be merged.

This merging can simplify some uses of #2d expressions. For example, consider this expression that captures subtyping relationships between a few of the Typed Racket numeric types, this time using a #2d match expression:

> #lang unstable/2d racket
> (require unstable/2d/match)
> (define (subtype? a b)
> #2dmatch
> ╔══════════╦══════════╦═══════╦══════════╗
> ║ a b ║ 'Integer ║ 'Real ║ 'Complex ║
> ╠══════════╬══════════╩═══════╩══════════╣
> ║ 'Integer ║ #t ║
> ╠══════════╬══════════╗ ║
> ║ 'Real ║ ║ ║
> ╠══════════╣ ╚═══════╗ ║
> ║ 'Complex ║ #f ║ ║
> ╚══════════╩══════════════════╩══════════╝)

There are a number of cell walls missing here, but this is still a well-formed #2d expression. In this case, the 2dmatch treats any of the situations that fall into the larger regions as the same.

In general, a #2d expression, when read, turns into an expression with at least two sub-pieces (not counting the initial name). The first is a sequence of numbers giving the widths of the top row of cells; the second is also a sequence of numbers, this time giving the heights of the leftmost column of cells. The remaining sequence describe the cells content. The first element of each is itself a sequence of coordinates, one for each of the cells that are connected together. The remaining elements are the subexpressions in the given cells.

For example, this:

> #lang unstable/2d racket
> '#2dex
> ╔══════════╦══════════╗
> ║ 0 ║ 1 ║
> ╠══════════╬══════════╣
> ║ 2 ║ 3 ║
> ╚══════════╩══════════╝

evaluates to

> '(2dex (10 10)
> (2 2)
> (((0 0)) 0)
> (((0 1)) 2)
> (((1 0)) 1)
> (((1 1)) 3))

and this

> #lang unstable/2d racket
> '#2dex
> ╔══════════╦══════════╦══════════╗
> ║ 0 ║ 1 2 ║ 3 4 ║
> ╠══════════╬══════════╩══════════╣
> ║ 5 ║ 6 ║
> ╚══════════╩═════════════════════╝

evaluates to

> '(2dex (10 10 10)
> (2 2)
> (((0 0)) 0)
> (((0 1)) 5)
> (((1 0)) 1 2)
> (((1 1) (2 1)) 6)
> (((2 0)) 3 4))

In addition, the cells coordinates pairs have source locations of the first character that is inside the corresponding cell. (Currently the span is always 1, but that may change.)

#### 32.1`` Editing 2D

DrRacket provides a number of keybindings to help editing #2d expressions. See DrRacket’s keyboard shortcuts.

#### 32.2`` 2D Cond

(require unstable/2d/cond) | package: unstable-2d

> syntax (2dcond cond-content)
> cond-content |  | = |  |
> question-row
> body-row
> ⋮
> question-row
> body-row
> ⋮
> else-row
> question-row |  | = |  | empty-cell question-cell ⋯
> |  | | |  | empty-cell question-cell ⋯ else-cell
> body-row |  | = |  | question-cell exprs-cell ⋯
> else-row |  | = |  | question-cell exprs-cell ⋯ else-cell
> question-cell |  | = |  |
> ╔═════════════╗
> ║question-expr║
> ╚═════════════╝
> empty-cell |  | = |  |
> ╔═══╗
> ║ ║
> ╚═══╝
> exprs-cell |  | = |  |
> ╔═════════════╗
> ║expr expr ...║
> ╚═════════════╝
> else-cell |  | = |  |
> ╔══════╗
> ║ else ║
> ╚══════╝

Evaluates the first row of question expressions until one of them returns a true value (signaling an error if none do), then evaluates the first column of question expressions until one of them returns a true value (signaling an error if none do), and then evaluates the cell in the middle where both point to, returning the result of the last expression in that cell.

#### 32.3`` 2D Match

(require unstable/2d/match) | package: unstable-2d

> syntax (2dmatch match-content)
> match-content |  | = |  |
> match-first-row
> match-row
> ⋮
> match-first-row |  | = |  | two-expr-cell match-pat-cell ⋯
> match-row |  | = |  | match-pat-cell exprs-cell ⋯
> two-expr-cell |  | = |  |
> ╔═════════════════╗
> ║col-expr row-expr║
> ╚═════════════════╝
> match-pat-cell |  | = |  |
> ╔═════╗
> ║ pat ║
> ╚═════╝
> exprs-cell |  | = |  |
> ╔═════════════╗
> ║expr expr ...║
> ╚═════════════╝

Matches col-expr against each of patterns in the first column of the table and matches row-expr against each of the patterns in the row row, and then evaluates the corresponding exprs-cell, returning the value of the last expression in that cell.

#### 32.4`` 2D Tabular

(require unstable/2d/tabular) | package: unstable-2d

> syntax (2dmatch tabular-content)
> tabular-content |  | = |  |
> tabular-row
> ⋮
> tabular-row
> ⋮
> style-cell
> tabular-row |  | = |  | tabular-cell ⋯
> tabular-cell |  | = |  |
> ╔════════════════╗
> ║tabular-expr ...║
> ╚════════════════╝
> style-cell |  | = |  |
> ╔═════════════════╗
> ║style-content ...║
> ╚═════════════════╝
> style-content |  | = |  | #:style style-expr
> |  | | |  | #:sep sep-expr
> |  | | |  | #:ignore-first-row
> > | style-expr |  | : |  | style?
> > | sep-expr |  | : |  | (or/c block? content? #f)
> > | tabular-expr |  | : |  | (or/c block? content?)

Constructs a tabular matching the given cells.

If a cell spans multiple columns, then the resulting tabular has 'cont in the corresponding list element. No cells may span rows.

The #:style and #:sep arguments are just passed to tabular.

If the #:ignore-first-row keyword is provided, then the first row of the 2dtabular expression is ignored. This can be used in case the first row of the rendered table should not have all of the columns (as #2d syntax requires that the first row contain a cell for each column that appears in the table).

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