JDriven Blog

Clojure Goodness: Set Default Value For nil Function Argument With fnil

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Hubert Klein Ikkink

The function fnil can be used to create a new function from an existing function where we define default values for arguments that can be nil. Especially when we want to use a function that we didn’t write ourselves this can be helpful to handle nil values in a consistent way. We can prevent for example a NullPointerException by setting a default value. We can define default values for a maximum of three arguments for the original function. When we invoke the function that is returned from the fnil function any extra arguments after the first arguments are simply passed on to the original function.

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Building a Magic Mirror

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Justus Brugman

Now it’s time for something completely different. Lately I’ve been watching some great videos from Matthew Perks, he has a YouTube channel called DIY Perks. This inspired me to pick up my own little project to create our own Magic Mirror.

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Clojure Goodness: Partition Collection Into Sequences

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Hubert Klein Ikkink

Clojure has the partition, partition-all and partition-by functions to transform a collection into a list of sequences with a (fixed) number of items. We can set the number of items in each sequence by providing a number as the first argument of the partition and partition-all functions. Any remainder elements are not in the resulting list of sequences when we use partition, but are when we use partition-all. We can also specify another collection to use values from to fill up the remainder as the third argument of the partition function.
Optionally we can specify an offset step value as a second argument using both functions. This mean a new partition sequence will start based on stepping through the original collection with the given step value.
Finally we can use a function to define when a new partition must start with the partition-by function. Every time the function returns a new value a new partition will begin.

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Awesome Asciidoctor: Image As Link Reference

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Hubert Klein Ikkink

To make an image linkable in Asciidoctor when formatted to HTML we must use the link attribute when we use the image macro. The value of the link attribute is the address where the user goes when clicking on the image. We can also specify extra link attributes like window to specify the target window for the link to open in.

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Clojure Goodness: Check Substring Is Part Of String

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Hubert Klein Ikkink

Sometimes we want to see if a string is part of another string. Or if the string value starts or ends with a certain string. In Clojure we can use the includes? function from the clojure.string namespace to check if a string is part of another string value. To see if a string starts with a certain value we can use the starts-with? function from the clojure.string namespace. And to check if a string ends with a given value we use ends-with? from the same namespace.

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Clojure Goodness: Getting Results From Multiple Functions With Juxt Function

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Hubert Klein Ikkink

The function juxt can be used to get results from multiple functions on the same argument in one go. We pass the functions we want to invoke as arguments to the juxt function. This results in a new function that will return a vector with the results from each original function that is passed to the juxt function. So the first element in the result vector is the result of the first function, the second element is the result of the second function and so on. The documentation of the juxt function shows this clearly as juxt a b c ⇒ [a(x) b(x) c(x)].

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Practical Money in Java

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Peter Steman

While investigating Protobuf I shot from the hip and wrote that: to model money, one should use BigDecimal. That’s the conventional wisdom and it is correct - in a lot of cases. It’s fine when you deal with one single currency and you are most of all concerned with the precision of financial calculations. But what are some other options? let’s find out.

For this exploration, I’ve defined some scenarios to see how the different options stack up to each other.

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Clojure Goodness: Reapply Function With Iterate To Create Infinitive Sequence

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Hubert Klein Ikkink

The iterate function create a lazy, infinitive sequence based on function calls. The iterate function takes a function and an initial value as arguments. The first element in the sequence is the initial value, next the function is invoked with the previous element as argument and this continues for each new element. Suppose we have a function #(+ 2 %) that adds 2 to the input argument. Then if we use this function with iterate and start with value 1 the first elements of the sequence will be 1, (+ 2 1), (+ 2 3), (+ 2 5). So first element is the initial value, next element is the invocation of the function with input argument 1. The result of this function is 3, which is then the input for the function to calculate the next element and so on.

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