str implements multiline strings with interpolation.
Interpolating a value of parameter a into the string is done by $a$
and interpolating anything with instance Show is $:a$.
Repetitive patterns can be made by # symbol using the following syntax:
#<var> in <list>: <interpolated string> (|<interpolated string>)#
Where (|<interpolated string>) denotes optional separator for the elements.
#i in myList: this is $i$|--#
Which will evaluate to
1--2--3 given myList of [1,2,3]
Multiline indentation is handled by aligning on smallest un-empty line after the first.
Pattern matching is not supported.