The Well-Known Text Arithmetic Expression Language (WAEL) is an experimental, domain-specific language for generating and manipulating geometry patterns. The language syntax aims to be a superset of Well-Known Text (WKT) with added support for programming features like variables, basic arithmetic, functions and comments. Geometries can be transformed using array programming features like geometry arithmetic and pipe transformations (see the Syntax section below for details).
Basic support is currently available for the following 2D geometries: POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, GEOMETRYCOLLECTION. Sections with an ⚠ experimental feature label indicate features that could be updated or modified in future versions.
Try out the language at geojsonscript.io with the WAEL code editor option selected.
Install dependency:
npm install wael-lib
Evaluate code using the evaluate() method:
import { Wael } from 'wael-lib';
const result = Wael.evaluate(`Point(1 1) + Point(2 2)`);
See the Terminal Usage section for instructions using the CLI program.
The following examples use language constructs and built-in functions to generate geometry patterns.
Create a 20x10 grid of points with 2-unit spacing starting from coordinates -110, 38:
Point(-110 38) + PointGrid(20, 10, 2)
Create the same grid and introduce random offsets:
Point(-110 38) + PointGrid(20, 10, 2)
|| Function(p => {
xOffset = 1 - Math:random() * 2;
yOffset = 1 - Math:random() * 2;
p + Point(xOffset yOffset)
})
Rotate a 20x10 grid of points around origin by 23 degrees:
PointGrid(20, 10, 4) | Rotate:bind(23, Point(0 0))
Create several nested circle polygons:
numRings = 5;
Generate numRings Function(i => {
ring = numRings - i;
PointCircle((ring * 2), (ring * 10)) | ToPolygon
})
The wael.ts script can be used to evaluate code and output the resulting WKT:
npx ts-node ./scripts/wael.ts --help
Following the build instructions, a wael binary application can be used:
wael --help
To evaluate code and output the resulting WKT, specify one or more input files:
wael ./myScript.wael
To output GeoJSON instead of WKT, add the --geojson flag:
wael ./myScript.wael --geojson
To evaluate expressions interactively in a read-eval-print loop (REPL), use the --interactive (or -i) flag.
wael -i
All evaluated files, including the interactive environment, will share the same scope. This means that any variables defined in a script file will be accessible in following scripts and the interactive environment, if specified. For example, in the following command, myConstants.wael variables will be accessible to myFunctions.wael, and variables in both scripts will be accessible in the interactive environment.
wael ./myConstants.wael ./myFunctions.wael -i
Expressions can be passed in directly with the --evaluate (or -e) flag.
wael -e "Point(1 1) + Point(2 2)"
Any variables defined in the --evaluate script can be used in following script files. For example, the following path.wael script references an undefined start variable:
start ++ GeometryCollection(Point(2 2), Point(3 3), Point(4 4))
When evaluated with the following command:
wael -e "start = Point(1 1)" path.wael
The start variable will be defined in the --evaluate argument and the output will be:
GEOMETRYCOLLECTION (POINT (1 1), POINT (2 2), POINT (3 3), POINT (4 4))
Define geometries using WKT syntax expressions:
GEOMETRYCOLLECTION(
POINT (30 10),
LINESTRING (30 10, 10 30, 40 40),
POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10)),
POLYGON ((35 10, 45 45, 15 40, 10 20, 35 10),
(20 30, 35 35, 30 20, 20 30))
)
Multiple expressions are separated by a semi-colon (;) and the last expression is returned after evaluation. For example, evaluating the code:
POINT (1 2);
LINESTRING (1 2, 3 4)
will result in LINESTRING (1 2, 3 4)
Expressions are white-space insensitive and case-insensitive, so the following syntax is also valid:
LineString (
1 2 ,
3 4
)
Comments begin with the # character:
# Napoli, Italy
Point(14.19 40.828)
Coordinate values can be expressed using basic numeric arithmetic (+ - * / ^ %):
Point((8 * 3) (-12 + 5)) # POINT (24 -7)
Geometries also support basic arithmetic:
Point(1 2) + Point(3 4) # POINT (4 6)
Array-like geometries support array programming operations:
LineString(1 1, 2 2, 3 3) + LineString(10 10, 10 10, 10 10); # LINESTRING (11 11, 12 12, 13 13)
LineString(1 1, 2 2, 3 3) - Point(10 10); # LINESTRING (-9 -9, -8 -8, -7 -7)
⚠ experimental feature
Array-like geometries can be combined using the concatenate (++) operator:
LineString(1 1, 2 2) ++ LineString(3 3, 4 4); # LINESTRING (1 1, 2 2, 3 3, 4 4)
MultiPoint(1 1, 2 2) ++ MultiPoint(3 3, 4 4); # MULTIPOINT (1 1, 2 2, 3 3, 4 4)
GeometryCollection(Point(1 1)) ++ GeometryCollection(Point(2 2)); # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2))
Points can be appended to point array-like geometries:
LineString(1 1, 2 2) ++ Point(3 3); # LINESTRING (1 1, 2 2, 3 3)
MultiPoint(1 1, 2 2) ++ Point(3 3); # MULTIPOINT (1 1, 2 2, 3 3)
GeometryCollection(Point(1 1)) ++ Point(2 2); # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2))
Non array-like geometries are concatenated into a GEOMETRYCOLLECTION:
Point(1 1) ++ Point(2 2); # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2))
Point(1 1) ++ Polygon((2 2, 3 3, 4 4, 2 2)); # GEOMETRYCOLLECTION(POINT (1 1),POLYGON ((2 2, 3 3, 4 4, 2 2)))
Variables are defined using the equal (=) operator. Supported data types include:
- Number
- Boolean:
True,False - Geometry:
Point,MultiPoint,LineString,MultiLineString,Polygon,GeometryCollection - Function
longitude = 2; # number
bool = True; # boolean
p = Point(longitude 3); # geometry
fn = Function(p => p + 1); # function
Functions are first-class and declared using the Function keyword:
getEquatorPoint = Function(longitude => Point(longitude 0));
They can be invoked using parentheses ():
getEquatorPoint(14.19) # POINT (14.19 0)
Functions can also accept multiple parameters and have function bodies spanning multiple lines. Similar to top-level expressions outside of a function, the last expression in the function body is used as the return value.
myFn = Function((x, y, last) => {
first = Point(x y);
LineString(first, last)
});
myFn(1, 2, Point(3 4)) # LINESTRING (1 2, 3 4)
Functions can have parameters bound using the bind() method:
Generate 10 Function(i => { x = Math:random() * 100; Point(x x) })
|| Round:bind(2)
# GEOMETRYCOLLECTION (POINT (18.98 18.98), POINT (14.26 14.26), ...)
Geometry properties and methods can be accessed using the accessor (:) operator:
p = Point(3 4);
p:type; # Point
p:x; # 3
p:y; # 4
g = GeometryCollection(Point(1 2), Point(3 4));
g:type; # GeometryCollection
g:numGeometries; # 2
g:geometryN(1); # POINT (3 4)
l = LineString(1 2, 3 4);
l:type; # LineString
l:numPoints; # 2
l:pointN(1); # POINT (3 4)
Geometry properties can be set by calling a method with an appropriate parameter. Since geometries are immutable, a new geometry instance is returned using the updated value:
p = Point(3 4);
p:x(5); # POINT (5 4)
p:y(6); # POINT (3 6)
p # POINT (3 4)
Boolean values True and False can be used in logical And, Or or negation ! expressions:
a = True;
b = False;
a And b; # False
a Or b; # True
!a; # False
Numeric values can be used in comparison expressions < <= > >= == !=, which return a boolean value:
a = Point(1 2);
b = Point(3 4);
a:x < b:x # true
Control flow can be dictated using If-Then-Else expressions:
result = If (Point(1 2):x < 3)
Then (LineString(1 1, 2 2, 3 3))
Else (Point(0 0));
result # LINESTRING(1 1, 2 2, 3 3)
All three parts of the If-Then-Else expression are required. The Then and Else blocks can contain multiple lines, similar to a function body.
points = GeometryCollection(Point(0 0), Point(0 0), Point(0 0), Point(0 0), Point(0 0));
If (points:numGeometries > 3) Then (
a = Point(1 2);
b = Point(3 4);
a + b
) Else (
a = LineString(1 1, 2 2);
b = LineString(3 3, 4 4);
a + b
) # POINT (4 6)
⚠ experimental feature
Multiple geometries can be generated using the Generate expression by specifying an iteration count and either a geometry or a function that returns a geometry. The set of all geometries returned from a Generate expression are collected into a GEOMETRYCOLLECTION.
Generate 3 Point(0 0); # GEOMETRYCOLLECTION(POINT (0 0),POINT (0 0),POINT (0 0))
Generate 3 Function(x => Point(x x)) # GEOMETRYCOLLECTION(POINT (0 0),POINT (1 1),POINT (2 2))
The iteration count can also be specified as a variable:
count = 3;
Generate count Point(0 0) # GEOMETRYCOLLECTION(POINT (0 0),POINT (0 0),POINT (0 0))
⚠ experimental feature
The output from any expression can be used as the input to another function with the pipe (|) operator:
Point(1 1) | Function(x => LineString(x, 2 2)) # LINESTRING (1 1, 2 2)
Each item in an array-like geometry can be mapped using a function with the double-pipe (||) operator:
LineString(1 1, 2 2, 3 3) || Function(x => x * x) # LINESTRING (1 1, 4 4, 9 9)
The array map index is also available as function parameter:
LineString(1 1, 2 2, 3 3) || Function((x, i) => x * i) # LINESTRING (0 0, 2 2, 6 6)
Each point in a geometry can be transformed using the pipe-all (|*) operator:
LineString(1.4325 1.5325, 2.23525 2.7453, 3.26474 3.34643) |* Round:bind(1) # LINESTRING (1.4 1.5, 2.2 2.7, 3.3 3.3)
⚠ experimental feature
Array-like geometries can be filtered using the filter (|~) operator:
LineString(1 1, 2 2, 3 3) |~ Function((p, i) => p:x <= 2) # LINESTRING (1 1, 2 2)
⚠ experimental feature
Array-like geometries can be reduced using the reduce (|>) operator:
LineString(1 1, 2 2, 3 3) |> Function((total, current, index) => total + current) # Point(6 6)
⚠ experimental feature
Data can be imported using Import expressions. For example, if the file etna.wael contains Point(14.99 37.75), it can be imported using:
data = Import('etna.wael');
data # POINT (14.99 37.75)
Supported data formats include WKT, GeoJSON, and WAEL.
⚠ experimental feature
Several built-in functions are provided to support geometry generation and transformation.
All JavaScript Math static properties and static functions are accessible from the Math variable:
pi = Math:PI; # 3.141592653589793
Math:round(pi) # 3
Flatten(g) - flatten all geometries in a GEOMETRYCOLLECTION
Flatten(GeometryCollection(Point(1 1), GeometryCollection(Point(2 2)))) # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2))
PointGrid(x, y, spacing) - create a grid of points with the given X and Y count, and (optional) spacing
PointGrid(20, 10, 2) # GEOMETRYCOLLECTION(POINT (0 0),POINT (0 2), ... POINT (38 18))
PointCircle(radius, count) - create a circle of points with a given radius and point count
PointCircle(5, 50) # GEOMETRYCOLLECTION(POINT (5 0),POINT (4.9605735065723895 0.6266661678215213), ... )
Rotate(angleDegrees, originPoint, geometry) - rotate a geometry by the specified degrees around an origin point
Rotate(23, Point(0 0), MultiPoint(1 1, 2 2, 3 3)) # MULTIPOINT (1.3112079320509338 0.5297935627181312, ... )
Round(precision, val) - round a number or Point coordinates with a given precision (defaults to 0)
Round(1, 1.255) # 1.3
ToLineString(g), ToMultiPoint(g), ToPolygon(g), ToGeometryCollection(g) - convert an array-like geometry of points to a different geometry type
list = GeometryCollection(Point(1 1), Point(2 2), Point(3 3));
ToLineString(list); # LINESTRING (1 1, 2 2, 3 3)
ToMultiPoint(list); # MULTIPOINT (1 1, 2 2, 3 3)
ToPolygon(list); # POLYGON ((1 1, 2 2, 3 3, 1 1))
ToGeometryCollection(list) # GEOMETRYCOLLECTION(POINT (1 1),POINT (2 2),POINT (3 3))
npm install
npm run build
To build the CLI binary, run:
npm run build-binary
The binary will be available at:
dist/bin/wael
npm test
WAEL is implemented with TypeScript using Ohm. When code is evaluated, geometries are stored in an intermediate representation (IR) as GeoJSON objects, which can then be transformed to either WKT or GeoJSON as output.
This project is made publicly available under the MIT license (see the LICENSE file).