Uiua

Uiua is a stack-based array language designed by Kai Schmidt. It uses concatenative evaluation (a context-free grammar) with a right-to-left ordering as in Polish notation. Like the SHARP APL family, arrays are flat with a homogeneous type; however, functions in Uiua are first-class values, and instead of boxes, niladic constant-valued functions are used to provide array nesting. The language supports tacit programming using stack manipulation primitives, and all complex functions must be defined this way as there is no explicit function form that allows local variables. Functions have a fixed number of input and output values, meaning the overloading of ambivalent functions is removed. Because of this, Uiua often splits APL primitives into two functions. Its primitives use Unicode glyphs including many not found in other languages. To avoid the need for a keyboard layout containing these, each primitive can also be spelled using a name that consists of lowercase letters (user-defined names must have at least one uppercase letter). By default, the language formats source files when run to convert these names into the corresponding glyphs.