A Haskell JSON parser built in the style of jQuery. Created from specifications provided in the University of Strathclyde's CS316: Functional Programming class.
For the original specification and build instructions, please see here. This new README is created for the purpose of documenting features available in this implementation.
After specifying the JSON file to load from as a command line argument, you will be prompted to enter a query. Queries can use any of these filters in combination.
Returns the input unchanged.
Input: {"a": 1, "b": 2}
Query: .
Output: {"a": 1, "b": 2}
Looks up a field in the object and returns the value associated with that field.
If the key contains disallowed characters, it will need to be surrounded with double quotes like this: .".a" or .[".a"]
Input: {"a": 1, "b": 2}
Query: .a
Output: 1
Input: {"a": {"b": 2}}
Query: .a.b
Output: 2
Input: {"a": {"...": 2}}
Query: .a.["..."]
Output: 2
Returns all the elements of an array.
Input: [1, 2, 3]
Query: .[]
Output:
1
2
3
Runs two filters on the input and concatenates the results in order.
Input: {"a": 1, "b": 2}
Query: .a, .b
Output:
1
2
Combines two filters by feeding the output of the first into the second. If the first filter produces multiple results, the second filter will be run on each of them.
Input: {"a": {"b": 2}}
Query: .a | .b
Output: 2
Strings, Booleans, null & positive Integers are all interpreted as their constant representations.
Takes two filters, applies them to the input, and adds the results together.
- Numbers are added by normal arithmetic.
- Anything added to null is unchanged.
- Arrays are concatenated together.
- Strings are concatenated together.
Input: {"a": 1, "b": 2}
Query: .a + .b
Output: 3
Input: {"a": 1, "b": 2}
Query: .a + null
Output: 1
Input: {"a": [1, 2], "b": [3, 4]}
Query: .a + .b
Output: [1, 2, 3, 4]
Input: {"a": "hello", "b": " world"}
Query: .a + .b
Output: "hello world"
Takes two filters, applies them to the input, and subtracts the result of the second from the first.
- Numbers are subtracted by normal arithmetic.
Input: {"a": 3, "b": 2}
Query: .a - .b
Output: 1
Takes two filters, applies them to the input, and multiplies the results together.
- Numbers are multiplied by normal arithmetic.
- Multiplying a string by a number will repeat the string that many times.
Input: {"a": 3, "b": 2}
Query: .a * .b
Output: 6
Input: {"a": "hi", "b": 3}
Query: .a * .b
Output: "hihihi"
Takes two filters, applies them to the input, and divides the result of the first by the second.
- Numbers are divided by integer division.
Input: {"a": 6, "b": 2}
Query: .a / .b
Output: 3
Takes two filters, applies them to the input, and returns the remainder of the first divided by the second.
- Numbers are divided by normal arithmetic.
Input: {"a": 5, "b": 2}
Query: .a % .b
Output: 1
Produces its input unchanged if the expression evaluates as truthy (anything except false or null), or nothing otherwise.
Input: {"a": 1, "b": 2}
Query: select(true)
Output: {"a": 1, "b": 2}
Takes a filter from either side, applies them to the input, and returns true if the results are equal or not equal respectively, or false otherwise.
Input: {"a": 1, "b": 2}
Query: .a == .b
Output: false
Takes a filter from either side, applies them to the input, and returns whether the first is less than, less than or equal to, greater than, or greater than or equal to the second respectively.
Input: {"a": 1, "b": 2}
Query: .a < .b
Output: true
Takes a filter from either side, applies them to the input, and follows standard boolean logic. Anything except False or null is considered truthy & will satisfy these filters. and has higher precedence than or.
Input: {"a": 1, "b": 2}
Query: .a > 0 and .b > 0
Output: true
Takes a filter, applies it to the input, and inverts the truthy value of the result.
Input: {"a": 1, "b": 2}
Query: not (.a > 0)
Output: false
- Queries that have not been parsed fully will be rejected with an error message.
- The
Transformertype has been altered toJSON -> Result [JSON]and reports appropriate errors on failure. - All functions have provided documentation.
A test suite has been implemented for every function written for this coursework, and can be found in ./src/Spec.hs.
.- Returns the entire JSON file..[]- Returns all the hills separately..[].Name- Returns the names of all the hills..[] | select(.Height > 1000) | .Name- Returns the names of all the hills over 1000m..[] | select(.Height > 1000 && .Country == "S") | .Name, .Height- Returns the names and heights of all the hills over 1000m in Scotland..[] | select(.Height > 1300 or not (.Height >= 50))- Returns all the hills over 1300m or under 50m..[] | select(.Country != "S")- Returns all the hills that are not in Scotland..[] | select(.Height > 1100) | .Name , (.Height | . - 1100)- Returns the names of all the hills over 1100m, and by how much they exceed 1100m.2 * 10 / 2 * (3 - 1) + 5- Returns 25.