Eggsy

A simple and uniform toy programming language written in JavaScript that I've been working on to help me understand how parsers work.

Eggsy is based on the Egg programming language project from Eloquent JavaScript, 3rd Edition

Syntax

Everything in Eggsy is an expression - the name of a variable, a number, a string, or an application (applications are used for function calls as well as for if or while statements).

Strings, Numbers and Variable Names

A string is a sequence of characters wrapped in double quotes, where characters in that sequence are anything but double quotes. Examples: "A string", "Mulan (1998)"

A number is a sequence of digits. Examples: 01, 114

Parentheses are not valid in a variable name. Neither are commas (,) or hashes (#). Other than these, variable names can consist of any non-whitespace characters that do not have a special meaning in the syntax. Examples: total, 4get

Applications

Applications are written by putting parentheses after an expression and having comma-separated arguments between those parentheses. (The number of arguments allowed depends on the construct being used.) Examples:

# define a variable named total and assign it a value of 10
define(total, 10)

if (==(exp, 0),
  1,
  *(base, pow(base, -(exp, 1))))

do

The do construct is used to represent doing multiple things in sequence.

do(define(total, 0),
  print("This is a string."),

  define(count, 1),

  # This is a comment

  while(<(count, 11),
    do(define(total, +(total, count)),
      define(count, +(count, 1)))),

  print(total)
)

Functions

A function construct treats its last argument as the function’s body and all arguments before that as the function’s parameters.

# create a function named subtractOne which subtracts one from the argument it is called with
do(define(subtractOne, fun(a, -(a, 1))),
    # print the result of calling subtractOne with an argument of 12
    print(subtractOne(12)))

Comments

As you must have guessed from the code examples above, comments are preceded with the # character. Everything from the # character to the end of a line is considered a comment and will be ignored.

# One more comment for the road
print("There's a comment above me.") # Another comment here

Operators

+(4, 1)   # 5

-(6, 2)   # 4

*(3, 3)   # 9

/(6, 2)   # 3

==(7, 7)   # true

<(7, 5)   # true

>(5, 7)   # true

Arrays

# create a new array
array(0, 1, 2, 3, 4)

# get the length of an array
length(array(0, 1, 2, 3, 4))

# return the nth element of an array
element(array(0, 1, 2, 3, 4), n)

Usage

Call the run function in main.js on a valid piece of code to evaluate it.

run(`
  do( print(element(array(0, 1, 2, 3, 4), 2)),
    print("Done."))
`);

Wryhder / Eggsy