EggJs Playground

EggJs Playground is a web based editor for a primitive programming language Egg built using Javascript. Egg is featured as an example project in the book Eloquent Javascript by Marjin Haverbeke.

Screenshots

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Some Things to Remember :

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• Everything is an expression in Egg. Even '+' or '-' which are operators in Javascript are treated as expressions.
• Each expression in Egg would be an object. Thus, it would contain a type property, which would describe the type of the expression.
• Type:- 'value' means strings or numbers.
• Type:- 'word' means names of variables
• Type:- 'apply' means applications, eg. if else blocks, while loops, etc.
• All apply expressions have additional operator and args property.
• Comment lines start with a '#' character

Basic Syntax :

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• print

  • Description :- Prints the given value onto the console
  • Example :- print('Hello World')

• define

  • Description :- Defines a variable with the given name and assigns it a value
  • Example :- define(x,10)

• set

  • Description :- Changes the value of a previously declared variable
  • Example :- set(x,11)

• if

  • Description :- Conditional statement. Takes 3 arguments - condition, expression to execute if true, expression to execute if false
  • Example :- if(<(x,5),print('small'), print('large'))

• array

  • Description :- Creates an array with the specified elements
  • Example :- define(arr, array(1,2,3))

• length

  • Description :- Returns the length of an array
  • Example :- length(arr)

• element

  • Description :- Returns the element at specified index in array. Throws an error if index out of bounds
  • Example :- element(arr, 0)

• do

  • Description :- Defines a block of code.
  • Example :- do(define(arr, array(1,2,3)), print(element(arr, 0)))

• while

  • Description :- Defines a while loop with condition and a loop body
  • Example :- while(>(x,0), do(print(x), set(x, -(x,1))))

• func

  • Description :- Defines a function with arguments and a body. Arguments are separated by commas and the last expression is body
  • Example :- func(a,b,print(+(a,b)))