pretty-print a map?

adamohern

The above is really hard on the eyes. I find it difficult to read. Is there a way to print out nested maps and arrays with better formatting?

kevin_o_toole_1

In FeatureScript, it's beneficial to define types for the data you're using. This lets you write functions that accept only that type, and overload functions for that type — including toString().

So something like:

// new type
export type MyType typecheck isMyType;
export predicate isMyType(value)
{
    value is map;
    isInteger(value.id);
    isLength(value.length);
    is3dLengthVector(value.endPoint);
    isAngle(value.axialRotation);
    is3dDirection(value.orientation);
}

// constructor
export function myType(id is number, length is ValueWithUnits, endPoint is Vector,
    axialRotation is ValueWithUnits, orientation is Vector) returns MyType
{
    return {"id" : id, "length" : length, "endPoint" : endPoint,
        "axialRotation" : axialRotation, "orientation" : orientation } as MyType;
}

// overloads
export function toString(value is MyType) returns string
{
    var out is string = "MyType:";
    for (var entry in value)
    {
        out ~= "\n" ~ entry.key ~ ": ";
        out ~= toString(entry.value);        
    }
    return out;
}

export function debug(value is MyType)
{
    // call debug() on the relevant data in this type
}

I'm not sure about your exact use case, but for sake of conciseness in the type, it might be nicer to group endPoint, axialRotation, and orientation into a single CoordSystem to start with (personally, I find it mind-numbing trying to do vector math unless I'm starting with a CoordSystem and can call fromWorld() everywhere).

In the future, we'd like to have a nicer way of presenting big chunks of native data by default (even when custom types aren't defined), but today, untyped data is printed as a big long literal.

kevin_o_toole_1

Update: I misinterpreted the state of std. Turns out, we do have a decent toString() method defined on maps. The trick is to actually call toString, before string concatenation.

println("my map is " ~ toString(myMap));
// or simply
println(myMap);

Making a type is still good practice, but for the pretty-printing, calling the preexisting toString() will be much better than what you're seeing above.