Function calls and other commands can be chained in the helm config by piping (pipelines) one command to the next e.g.
apiVersion: v1
kind: ConfigMap
metadata:
name: {{ .Release.Name }}-configmap
data:
myvalue: "Hello World"
drink: {{ .Values.favorite.drink | quote }}
food: {{ .Values.favorite.food | upper | quote }}
The last line of the example above passes the favorite food field to the upper function, and then in turn to the quote function.