codegen.js

var parser = require('./grammar').parser;

var program = " \
x is 5. \
y is 6. \
z is x + y. \
 \
show z. \
";

function main () {
    var ast = parser.parse(program),
        source = codegen(ast);

    print(source);
}

function codegen (ast) {
    switch (ast[0]) {
        case 'Program':
            return codegenList(ast.slice(2));
        case 'NumberLit':
            return ast[1].val;
        case 'IdentExpr':
            return ast[1].name;
        case 'AddExpr':
            return codegen(ast[2]) + ' + ' + codegen(ast[3]);
        case 'IsStmt':
            return ast[2] + ' = ' + codegen(ast[3]) + ';\n';
        case 'ShowStmt':
            return 'print('+codegen(ast[2])+');\n';
        default:
            throw 'Unknown statement/expression: '+ast[0];
    }
}

function codegenList (list) {
    return list.reduce(function (prev, curr) {
        return prev + codegen(curr);
    }, '');
}

main();