First

First ( or   and also called Disclose) is a monadic function in nested APLs which extracts the first element in ravel order from its argument, or, if the argument is empty, returns its prototype. The glyph used varies by dialect. In a nested APL, First reduces the positive depth of an argument other than a simple scalar by at least one; in a flat APL it does not change the depth. A flat array language may also use the Head function to get the first major cell of its argument rather than the first 0-cell. In this case First can be obtained by taking the Head of the Ravel of the argument.

Lessons

 * APL Cultivation

Documentation

 * Dyalog
 * APLX
 * BQN