c-brenn/shapes

DSL for creating SVG shapes

Shapes

A DSL for describing shapes and a web server that renders them as SVGs.

The text box will highlight red on invalid input. The SVG is updated automatically when the input is valid.

Compile & run

$ stack setup && stack build
$ stack exec shapes

About

This is a solution to a college assignment aimed at learning about implementing and using DSLs.

It implements custom Shapes DSL for describing the shapes and their attributes. The web service is implemented using Scotty - a Haskell package that provides a DSL for describing simple web services.

The frontend uses Elm, making use of FRP which we covered earlier in the course.

Shapes DSL

A Drawing is [Object], an Object is a triple: ([Transform], Shape, [Style]).

Transform

The following transforms are available:

data Transform
  = Identity                -- does nothing
  | Translate Double Double -- translates x and y
  | Scale Double Doublie    -- scales x and y
  | Rotate Double           -- rotates by an angle in degrees
  | Skew Double Double      -- skews x and y by angles in degrees
  | Transform :+: Transform -- combines two transformations

In a [Transform] any Translate should come after any Scale, as in the other order, the Scale will also be applied to the translation.

Shape

The following shapes are available:

data Shape = Empty
           | Circle
           | Square

Style

The following styles are available:

data Style = Fill Colour
           | Stroke Colour
           | StrokeWidth Double

Colours

The following colours are available:

data Colour
  = Black
  | Blue
  | Gray
  | Green
  | Navy
  | Purple
  | Red
  | RGB Int Int Int
  | Silver
  | White
  | Yellow