Advanced Exercism • powershell

Bob

Challenge Overview

Bob is a lackadaisical teenager. In conversation, his responses are very limited.

Visit the bob exercise on Exercism to read the full instructions and download the exercise files.

Dig Deeper

regex switch

Using `regular expression`

function Get-BobResponse() {
    [CmdletBinding()]
    Param(
        [string]$HeyBob
    )
    switch -Regex -CaseSensitive ($HeyBob.TrimEnd()) {
        "^[A-Z ]+\?$"           {"Calm down, I know what I'm doing!"; break}
        "^$"                    {"Fine. Be that way!"}
        "\?$"                   {"Sure."}
        "^[^a-z]*[A-Z][^a-z]*$" {"Whoa, chill out!"}
        Default                 {"Whatever."}
    }
}

We begin by trimming the input from the end, then use it as input for the switch statement with -Regex and -CaseSensitive flags to start matching against patterns. By default PowerShell will match insensitively, so the second flag is needed to check for the yelling condition.

    switch -Regex -CaseSensitive ($HeyBob.TrimEnd())

The first case we should consider is the combined conditions of both yelling and question. Which mean we should match for uppercase letter and space with at least one appearance, and a question martk at the end. We break out of the switch statement if this got a match.

    "^[A-Z ]+\?$"           {"Calm down, I know what I'm doing!"; break}

Then we can match individual cases that does not share conditions. silence pattern match nothing from beginning to end, question pattern match for a question mark at the end, and yelling match for uppercase letter. If none of the patterns got a match, then we return the default response.

    "^$"                    {"Fine. Be that way!"}
    "\?$"                   {"Sure."}
    "^[^a-z]*[A-Z][^a-z]*$" {"Whoa, chill out!"}
    Default                 {"Whatever."}

Note : This approach is not recommended for new learners.

Regex.

conditional bools

Using `if` and `boolean` values

function Get-BobResponse() {
    [CmdletBinding()]
    Param(
        [string]$HeyBob
    )
    $Greet = $HeyBob.TrimEnd()

    $IsSilence  = -not $Greet.Length
    $IsQuestion = $Greet[-1] -eq '?'
    $IsYelling  = $Greet.ToUpper() -ceq $Greet -and $Greet -match "[A-Za-z]"

    if ($IsSilence) { return "Fine. Be that way!" }
    if ($IsQuestion) {
        if ($IsYelling) { return "Calm down, I know what I'm doing!" }
        return "Sure."
    }
    if ($IsYelling) {return "Whoa, chill out!" }
    "Whatever."
}

First, we remove all the spaces at the end of the string, this will help further operations easier to perform.

    $Greet = $HeyBob.TrimEnd()

Now, we understand that the logic of the exercise is mainly based on three different conditions : silence, yelling or question. So we created three variable that will return a boolean value after their evaluation.

IsSilence : we test if the string has any length (the previous trim operation helped facilitate this).

IsQuestion : we test if the last character of the string is a question mark (the previous trim operation helped facilitate this).

IsYelling : we test if the string stay the same after turning uppercase, and if the string has any letter inside it. The second part is crucial, because for example “1 2 3 4” to uppercase is still the same however it is not considered as a proper yelling response.

    $IsSilence  = -not $Greet.Length
    $IsQuestion = $Greet.EndsWith('?')
    $IsYelling  = $Greet.ToUpper() -ceq $Greet -and $Greet -match "[A-Za-z]"

Lastly, it is just a matter of using if combine with the conditions based on the rules to return the correct response. Since there are some overlap conditions between some responses, a correct order of if statements and the return values is important. In this case either IsQuestion or IsYelling should be below the combination of IsQuestion and IsYelling.

    if ($IsSilence) { return "Fine. Be that way!" }
    if ($IsQuestion) {
        if ($IsYelling) { return "Calm down, I know what I'm doing!" }
        return "Sure."
    }
    if ($IsYelling) {return "Whoa, chill out!" }
    "Whatever."

If statement.

Boolean.

Source: Exercism powershell/bob