Expressions-only ECMAScript

script.js

// This gist plays around with a subset of ECMAScript6 (ES2015) that only uses expressions (except for the 'Program' const declaration).

/* Some rules:

 * Arrow functions that evaluate an expression are the only kinds of functions allowed.
 * All variables are declared as function parameters. 
 * If you want to scope variables, use the following format of an arrow function in parentheses:
    ((variables,to,declare,in,function,scope)=>(expressions,within,which,you,will,use,said,variables))()
 * No return statement - the last expression in a list of expressions is what is returned.
 * No Generators :( Or async/await :( 
 * Loops are done with recursive functions!
 * Class expressions aren't allowed - as they use curly braces, they have to contain statements.
 * Where are the semicolons and curly braces? Well, use commas within a set of parentheses.
 * First parameter to Program is a standard library of sorts, usually window or global with FOR, WHILE and DOWHILE.
 */
 
const Program = ({FOR,WHILE,UNTIL,DOWHILE,DOUNTIL,SWITCH,IF,...stdlib}, vars, to, declare, at, run) => (console.log(stdlib));

// This declares expression-only loops/conditionals!
const FOR = (init,test,step,body)=>((init?init:step)(),(test()?FOR(null,test,step,body):null)),
      WHILE = (test,body)=>(test()?(body(),WHILE(test,body)):null),
      UNTIL = (test,body)=>(!test()?(body(),UNTIL(test,body)):null),
      DOWHILE = (test,body)=>(body(),(test()?DOWHILE(test,body):null)),
      DOUNTIL = (test,body)=>(body(),(!test()?DOUNTIL(test,body):null)),
      SWITCH = (disc, tests)=>(tests[disc]?tests[disc]:tests[void 0])(),
      IF = (...tests)=>(tests.length>0?(tests[0][0]?test[0][1]():IF(...tests.slice(1))):null);

// This actually runs the program :)
Program({FOR,WHILE,UNTIL,DOWHILE,DOUNTIL,SWITCH,IF,...(window?window:global)});