# String

• string_concat(?a, ?b, ?res): Concatenate two strings.

At least two arguments must be grouneded. Resolves if a + b = res. If one of the argument is ungrounded, this predicate constrains it so that the statement is true, by either concating the two strings or removing a prefix or suffix from res.

f-strings act as a syntatic sugar for this predicate: X = f"${a}(content of b)", X = f"(content of a)${b} or X = f"${a}${b}" is equivalent to string_concat(a, b, X).

Due to the limitation of our logic resolution algorithm, this predicate can not be part of a recursion. For example, a(X) :- string_concat("a", Y, X), a(Y) is not allowed.

• string_length(+str, -len): Get the length of a string.