Introduction
You're a huge fan of geocaching, which combines your love for the outdoors with a love for solving puzzles.
Whilst the local geocaching website lists the GPS coordinates of all caches, it does not support creating an efficient route for gathering them.
It so happens you have pathfinding software installed on your machine, but it uses a different GPS format from the geocaching website.
To feed the data into the pathfinding software, you'll need to parse the degrees and hemisphere for both the latitude and longitude of each GPS coordinate on the website.
Instructions
Your task is to parse GPS coordinates.
Each coordinate is formatted using the Decimal Degrees format variant with explicit hemispheres:
<LATITUDE_DEGREES> <LATITUDE_HEMISPHERE>, <LONGITUDE_DEGREES> <LONGITUDE_HEMISPHERE>
These are the allowed values for each individual component:
-
<LATITUDE_DEGREES>: a floating-point number in the range 0..90 (inclusive)
-
<LATITUDE_HEMISPHERE>: either N or S
-
<LONGITUDE_DEGREES>: a floating-point number in the range 0..180 (inclusive)
-
<LONGITUDE_HEMISPHERE>: either E or W
For example, "48.8584 N, 2.2945 E" parses into:
-
<LATITUDE_DEGREES>: 48.8584
-
<LATITUDE_HEMISPHERE>: N
-
<LONGITUDE_DEGREES>: 2.2945
-
<LONGITUDE_HEMISPHERE>: E
You have 11 tasks, in which you'll incrementally parse GPS coordinates.
You'll be using Prolog's Definite Clause Grammar (DCG) support, which are designed to parse structured text.
To help you get started, the stub file already includes the dcg/basics library via:
:- use_module(library(dcg/basics)).
1. Parse a comma
Implement the comma rule to parse a single comma (","):
?- string_codes(",", Codes), phrase(comma, Codes).
2. Parse a space
Implement the space rule to parse a single space (" "):
?- string_codes(" ", Codes), phrase(space, Codes).
3. Support all whitespace (except newlines)
Modify the space rule to parse all whitespace, except for newlines:
?- string_codes("\t", Codes), phrase(space, Codes).
?- string_codes("\n", Codes), phrase(space, Codes).
false.
4. Parse the latitude's hemisphere
The hemisphere of the latitude can be either "N" or "S", which should be parsed to the north or south atom.
Implement the latitude_hemisphere rule to parse the latitude's hemisphere:
?- string_codes("N", Codes), phrase(latitude_hemisphere(Hemisphere), Codes).
Hemisphere = north.
5. Parse the longitude's hemisphere
The hemisphere of the longitude can be either "E" or "W", which should be parsed to the east or west atom.
Implement the longitude_hemisphere rule to parse the longitude's hemisphere:
?- string_codes("E", Codes), phrase(longitude_hemisphere(Hemisphere), Codes).
Hemisphere = east.
6. Parse degrees
The degrees of a longitude or latitude ire defined as a floating-point number.
Implement the degrees rule to parse floating-point numbers:
?- string_codes("748.012", Codes), phrase(degrees(Degrees), Codes).
Degrees = 748.012.
7. Parse latitude degrees
Latitude degrees are not just floating-point numbers, but floating-point numbers in the range 0..90 (inclusive).
Implement the latitude_degrees rule to parse latitude degrees using the above range:
?- string_codes("48.745", Codes), phrase(latitude_degrees(Degrees), Codes).
Degrees = 48.745.
?- string_codes("117.844", Codes), phrase(latitude_degrees(Degrees), Codes).
false.
8. Parse longitude degrees
Longitude degrees are not just floating-point numbers, but floating-point numbers in the range 0..180 (inclusive).
Implement the longitude_degrees rule to parse longitude degrees using the above range:
?- string_codes("178.773", Codes), phrase(longitude_degrees(Degrees), Codes).
Degrees = 178.773.
?- string_codes("-22.523", Codes), phrase(longitude_degrees(Degrees), Codes).
false.
9. Parse latitude
Latitudes have two parts: their degrees and hemisphere, which are separated by a space.
Implement the latitude rule to parse a latitude:
?- string_codes("56.101 N", Codes), phrase(latitude(Degrees, Hemisphere), Codes).
Degrees = 56.101,
Hemisphere = north.
10. Parse longitude
Latitudes have two parts: their degrees and hemisphere, which are separated by a space.
Implement the latitude rule to parse a latitude:
?- string_codes("143.889 W", Codes), phrase(longitude(Degrees, Hemisphere), Codes).
Degrees = 143.889,
Hemisphere = west.
11. Parse coordinate
Coordinates have two parts: their latitude and longitude, which are separated by a comma followed by a space.
Implement the coordinate rule to parse both the latitude (degrees and hemisphere):
?- string_codes("48.8584 N, 2.2945 E", Codes), phrase(coordinate(Latitude, LatitudeHemisphere, Longitude, LongitudeHemisphere), Codes).
Latitude = 48.8584,
LatitudeHemisphere = north,
Longitude = 2.2945,
LongitudeHemisphere = east.
