Disclose

or Reveal is a monadic function in nested APLs which reduces the level of nesting of an array. Early experiments in array nesting usually defined a primitive to extract the contents of a nested scalar, but did not always specify how it should behave on an array. Jim Brown's "A Generalization of APL", stated that it "may be undefined" on non-scalar arrays. However, all dialects do define it on non-scalars, but with differing definitions. Some dialects, for example Dyalog APL, have it extract the argument's initial element in ravel order, while others, for example APL2 have it combine the array's elements (requiring conforming shapes or padding with fill elements). Depending on which approach is taken, it is recommended to use the unambiguous names First and Mix for these two functions.

For a discussion of all uses of the glyph, see Right Shoe.