Too many languages

There are thousands of programming languages.

The purpose of a programming language is to express programs. The
purpose of learning programming languages is to build up a toolbox for
reasoning about and synthesizing programs in any one given language.

There are diminishing returns on learning programming languages, and
time is scarce.

Therefore one must select between programming languages to study.

A good selection of languages has both
+ breadth
  + satisfies a number of real world economic needs.
+ focus
  + exploits similarity between languages and incremental learning.
  + some unifying basis

A good member of a particular selection meets a number of the
following criteria:
+ Satisfies one particular school of thought on programming languages.
+ Significant difference from predecessors
+ Significant influence on successors
+ Economically significant
+ Advanced i.e. no direct, established and proven heir.
+ A good language.
  + Easy to express programs with
  + Easy to read programs expressed with
  + Easy to reason about programms expressed with

No one of these criteria are sufficient or even necessary conditions.

A bad member satisfies the opposite criteria.

>>69
Which word do you not understand? http://en.wikipedia.org/wiki/Universal_function

In layman's terms, a program written for some abstract machine (which is to say, an index in some particular Goedel numbering) can't possibly tell if it's executing on said machine "directly", like implemented in hardware or something, or inside an arbitrary number of evaluation (interpretation or compilation) layers in arbitrary abstract machines. Maybe even infinite number of such layers.

This is one of the most fundamental results in Computer Science. Why would people reject the eternal mathematical purity of an abstract machine and fetishize irrelevant transient hardware implementation details? Pig disgusting!

(maybe they never did low-level programming themselves and mistakenly believe it to be some sort of lost Eden? I did, it's dirty and exhausting, there's nothing magical about it)