While and when

[F.K]

Hi,
I read, In my English course and on the net, that we can use "When" to join two sentences one of them is in the past simple tense and the other is in the past continuous tense, and "When" takes the short action. like this:
I was walking to school.
I saw Sally.
I was walking to school when I saw Sally.

Please tell me what is wrong with:" When I was walking to school I saw sally". When here is taking the long action.

And as a completion of the rule, we can also use "While", but it takes always the long action. Like: "While I was walking I saw Sally." I don't complain this, but could this long action be in simple tense like the past simple tense" I changed while she cooked"?

Thanks :)

[Tdol]

You can use 'when' with the progressive form. I think it's not so much a rule- while gives more emphasis to the duration, but your example works for me. 'I was walking to school while I saw Sally' doesn't, however. When youhave two actions of equal duration, you can link them with 'while' in both the past simple and progressive forms.