First Stab at parenthesis
There are two ways in which our tokenizer might encounter parenthesis. The first is to group a lower-precedence operator, as in:
- (3 + 4) * 6
The next is in the use of function calls.:
- f(4)
For now, we want to pull out the () as tokens. We’ll allow something at a higher level to determine the context.
- Create a first test to see what happens when we use (:
@{expression = '(a)'; expected = @('(', 'a', ')')}- Interesting, this works. I’m skeptical that we’ve got it working as needed. Knowing a little bit about the code, I’ll add another test:
@{expression = '(())'; expected = @('(', '(',')', ')')}- There’s the failure I’m expecting:
[-] Should convert (()) to ( ( ) ) 102ms
Expected string length 1 but was 4. Strings differ at index 1.
Expected: {(}
But was: {(())}
------------^
22: $result[$i] | Should be $expected[$i]
at Invoke-LegacyAssertion, C:\Program Files\WindowsPowerShell\Modules\Pester\4.0.8\Functions\Assertions\Should.ps1: line 190
at <ScriptBlock>, C:\Users\Brett\src\shunting_yard_powershell_3\Tokenizer.Tests.ps1: line 22- Now it’s time to update the code just a touch. Rather than changing how to handle operators, I’ll add another match:
if (-not $this.recordIfMatches([ref]$expression, '^([()])', $result)) {
if (-not $this.recordIfMatches([ref]$expression, '^([\d\w]+)', $result)) {
$this.recordIfMatches([ref]$expression, '^([^\d\w\s]+)', $result)
}
}
}- Run your tests, that seems to work.
- Now is a good time to commit your code. After this, it seemed like there was a pattern in the code that I could represent with an array and a loop. Here’s another version that also works. I’m not sure if I like this better or not.
static [Array]$regex = @( '^([()])', '^([\d\w]+)', '^([^\d\w\s]+)' )
[ArrayList]interpret([String]$expression) {
$result = [ArrayList]::new()
while ($expression.Length -ne 0) {
$expression = $expression -replace ('^\s+', '')
foreach ($r in [Tokenizer]::regex) {
if ($this.recordIfMatches([ref]$expression, $r, $result)) {
break
}
}
}
return $result
}
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