J vs Common Lisp

3 classes of operators (verbs, adverbs, and conjunctions) with verbs the most basic function that take either 1 or 2 (infix) parameters. Operators allow function composition with a minimum of parentheses.

J also supports multiline functional definitions similar to BASIC/Pascal. Including error handling.

Each built in operator is a C/asm function, and special code further optimizes some operator combinations. Result is optimized C speed from quick parsing. Array orientation parses and compiles a function once, and applies it to all array items.

Still actively developed, but most recent changes have been in libraries and IDE and platform support.
Language is considered "perfected"... though not quite.

Complete core programming functional tools allow writting programs and libraries without imports.

(... within each of the 3 operator classes) makes reading code easier. Very simple parsing rules.

Almost all aspects of the language are designed with interactive/repl use in mind.

SLIME (Superior Lisp Interaction Mode for Emacs).

It is easy to recover from errors. Error resolution can be determined by the user at the REPL.

The state of the program may be saved and reloaded as an image, supporting safer modification of the running program. New code may be compiled into the image as the program runs, while late binding ensures that symbol redefinitions take effect throughout the program.

Some compilers such as SBCL can be faster than C or other low-level languages, and most compilers can generate fast native code.