How to use the adaptive-expressions.ReturnType function in adaptive-expressions

switch (pos) {
                case 0:
                    if (typeof val !== 'string') error = `${expr} does not have a path.`
                    break
                case 1:
                    if (typeof val !== 'object') error = `${expr} does not have bindings.`
                    break;
                case 2:
                    if (typeof val !== 'number') error = `${expr} does not have a numeric replication count.`
                    break;
                case 3:
                    if (typeof val !== 'string') error = `${expr} does not have a string random seed.`
            }
            return error
        }),
    expr.ReturnType.String,
    e => expr.FunctionUtils.validateOrder(e,
        [expr.ReturnType.Number, expr.ReturnType.String],
        expr.ReturnType.String,
        expr.ReturnType.Object))

    e => expr.ExpressionFunctions.validateOrder(e, [expr.ReturnType.String], expr.ReturnType.String))

e => expr.FunctionUtils.validateOrder(e,
        [expr.ReturnType.Number, expr.ReturnType.String],
        expr.ReturnType.String,
        expr.ReturnType.Object))

let name = args[0]
            let locale = args.length > 1 ? args[1] : 'en-us'
            return generateWords(name, locale).join(' ')
        },
        (val, expr, pos) => {
            let error
            switch (pos) {
                case 0:
                    if (typeof val !== 'string') error = `${expr} does not have a name string.`
                    break
                case 1:
                    if (typeof val !== 'string') error = `${expr} does not have a locale string.`
            }
            return error
        }),
    expr.ReturnType.String,
    e => expr.ExpressionFunctions.validateOrder(e, [expr.ReturnType.String], expr.ReturnType.String))

export let PhrasesEvaluator = new expr.ExpressionEvaluator('phrases',
    expr.ExpressionFunctions.apply(
        args => {
            let name = args[0]
            let locale = args.length > 1 ? args[1] : 'en-us'
            let min = args.length > 2 ? args[2] : undefined
            let max = args.length > 3 ? args[3] : undefined
            return Array.from(generatePhrases(name, locale, min, max))
        },
        (val, expr, pos) => {
            let error
            switch (pos) {
                case 0:
                    if (typeof val !== 'string') error = `${expr} does not have a name string.`