NOTE: For simplicity sake the following explanation is not 100% technically correct.
Each moment in Harlowe’s History represented by a Passage data-map object, and each of those Passage data-map objects has a known set of properties. You can see the names of those properties by looking at the documentation of the
When you supply a lambda as a conditional for the (history:) macro call the its keyword is used to represent each Passage data-map object that will be evaluated.
So if you want to only consider History moments where the Passage’s name equal to “Water” then you would use a lambda like the following…
(history: where its name is "Water")
And if you only wanted to show a link when the Array returned by above
(history:) macro call didn’t contain any elements then you would do something like the following…
(if: (history: where its name is "Water")'s length is 0)[[[* Go drink the water.|Water]]]