'use strict'; 
function evalToString(ast){ 
switch (ast.type){ 
case 'StringLiteral': return ast.value; 
case 'BinaryExpression': if (ast.operator !== '+') { 
throw new Error('Unsupported binary operator ' + ast.operator)
} 
return evalToString(ast.left) + evalToString(ast.right); 
default : { 
throw new Error('Unsupported type ' + ast.type)
} 
} 
} 
module.exports = evalToString;