Concatenation of a list of strings

The concat and sum commands concatenate elements of a list of strings together into a single string.

concat and sum both take L, a list of strings.
concat(L) and sum(L) both return the string obtained by lst concatenating strings from L together in the given order.

The join command concatenates a list of strings after inserting a specified separator string between adjacent elements.

join takes two arguments:
- sep, a string specifying the separator.
- L, a list of strings s₁,s₂,…,s_n.
join(sep,L) returns the string s1+sep+s2+sep+..+sn.

The cumSum command works on strings like it does on expressions by doing partial concatenation (see Section 6.3.26).

cumSum takes L, a list of strings.
cumSum(L) returns a sequence of strings where the element of index k is the concatenation of the strings in L with indices 0 to k.

sum("Hello, ","is ","that ","you?")

“Hello, is that you?”

join(" ",["Hello,","is","that","you?"])

“Hello, is that you?”

cumSum("Hello, ","is ","that ","you?")

“Hello, ”,“Hello, is ”, “Hello, is that ”,“Hello, is that you?”