tonykuttai / BuildingEvaInterpreter

Building an Interpreter for the Language Eva in Javascript

BuildingEvaInterpreter

Building an Interpreter for the Language 'Eva' in Javascript

Design Goals

• Simple syntax: S-expression
• Everything is an expression
• No explicit return, last evaluated expression is the result
• First-class functions
  • assign to variables
  • Pass as arguments
  • return as values
• Static Scope: all functions are closures
• Lambda functions, Immediately Invoked Lambda Expressions (IILE)
• Functional programming
• Imperative programming
• Namespaces and modules
• OOP
  • Class-based
  • prototype based

Functions

Native functions

• +, -, *, /, %
  • Natively supported operations
  • They are defined in the global enviroment
  • Example Usages:
    • (+ 1 5)
    • (* 3 4)
    • (+ 1 (* 4 6))

User defined Functions

• Functions can be declared as: (def square (x) (* x x))
• Invoked by: (square 4)

Lambda expression

• Create an anonymous function
• Lambda function:

  •  (def onClick (callback)
         (begin
             (var x 10)
             (var y 20)
             (callback (+ x y))
         )
     )            
     (onClick (lambda (data) (* data 10)))
    

• Immediately Invoked Lambda Expressions :

  • ((lambda (x) (* x x)) 2)
    

  • call lambda with an input argument and return the value
• Save lambda to a variable

  • (var square (lambda (x) (* x x)))
    (square 2)
    

Dependencies

syntax-cli

Install it from npm

sudo npm install -g syntax-cli
syntax-cli --help

References

Use Syntax-cli to test the grammar

syntax-cli --grammar parser/eva-grammer.bnf --mode LALR1 --parse '42'
syntax-cli --grammar parser/eva-grammer.bnf --mode LALR1 --parse '42' --tokenize
syntax-cli --grammar parser/eva-grammer.bnf --mode LALR1 --parse '(+ 5 foo)'

Generate the eva Parser

syntax-cli --grammar parser/eva-grammer.bnf --mode LALR1 --output parser/evaParser.js

All credits to the original author of this course: Dmitry Soshikinov