Use the LETjs frontend interpreter here https://hoenn.github.io/LETjs/
LET is a programming language originally described in Scheme by Daniel P. Friedman and Mitchell Wand in Exploration of Programming Languages.
This is an implementation of LET created in JavaScript using jison to generate the parser.
The LET language is a toy language with a very basic grammar. A program consists of a single expression which may be made up of multiple expressions itself.
let x = 5 in x Result: 5
let a = 3 in let y = 2 in -(x,y) Result: 1
let x = 3 in let y = 3 in if zero?(-(x,y)) then 1 else 0 Result: 1
Clone the repository
$ git clone https://github.com/Hoenn/LETjs.git
Install dependencies (from within LETjs directory)
$ npm install
The LET language can be interpreted using Repl.js. To launch the REPL
$ node Repl.js
Using the REPL
LET> 5
LET> let x = 5 in x
To see the Abstract Syntax Tree of your programs the REPL can be launched with 'AST' as an argument.
$ node Repl.js AST
To disable colors
$ node Repl.js AST --no-color
The LET.jison and LET.jisonlex files are the backbone of the language. If modified they must be recompiled with Jison to generate a new LET.js file. The HTML frontend must also be recompiled if the main.js file is modified. Add jison and browserify to your global node command line tools
$ npm install -g jison
$ npm install -g browserify
To recompile LET.js and bundle.js on bash
$ ./build.sh
This script simply runs the follow commands
$ jison grammar/LET.jison grammar/LET.jisonlex -o grammar/LET.js
$ browserify docs/main.js -o docs/bundle.js
Program :: Expression
Expression :: Number
Expression :: Id
Expression :: "zero?" "(" Expression ")"
Expression :: "-" "(" Expression "," Expression ")"
Expression :: "+" "(" Expression "," Expression ")"
Expression :: "*" "(" Expression "," Expression ")"
Expression :: "let" Id "=" Expression "in" Expression
Expression :: "if" Expression "then" Expression "else" Expression
Expression :: "proc" "(" Id ")" Expression
Expression :: "(" Expression " " Expression ")"
Expression :: "letrec" Id "(" Id ")" "=" Expression "in" Expression
Expression :: "begin" ExprSeq "end"
Expression :: "set" "(" Id "," Expression ")"
ExprSeq :: Expression
ExprSeq :: Expression ";" ExprSeq