As I went through the Wealth Lab Programming Guide I came across some useful functions,
like "PeakBar" and "ThroughBar".

For further details I looked in the WL QuickRef, WL User Guide and the Programming Guide itself.
There I didn't find further details, but finally I found a description on WealthLab Wiki.

But if I wouldn't have known that these functions exist, I wouldn't have looked for them.

Is there a list of all the functions which WL offers for programming ?

QUOTE:
But if I wouldn't have known that these functions exist, I wouldn't have looked for them.

In the Indicators window, click on "More info..." It will take you to the indicator's online help page in the Wiki (usually). This shortcut applies to any indicator from any installed indicator library: standard indicators, TASCIndicators, or Community Indicators.

QUOTE:
Is there a list of all the functions which WL offers for programming ?

Please see this FAQ: Is there a documentation for WealthLab.dll class procedures and methods?

PeakBar/TroughBar are not functions. These are indicators. Almost everything within Wealth-Lab is extendable, that is the modular design, and Wealth-Lab may continue to work even if you remove the Standard Indicators library. It was decided that unlike built-in methods, indicators (DataSeries) will be documented online (in the Wiki).

Thanks a lot.
The indicators lists give a very good overview.