subchars/[4,5]

subchars/[4,5] are identical to substring/[4,5] (lib-txp-sub-substring) except that the second argument, B, is a list of character codes, not a text object.

subchars(+ABC, ?B, ?LenA, ?LenB, ?LenC)

subchars(+ABC, ?B, ?LenA, ?LenB)

are true when

• ABC is a text object,
• B is a list of character codes (it may be empty),
• ABC can be broken into three pieces A, B, and C,
• LenA is the length of A,
• LenB is the length of B, and
• LenC is the length of C.

     | ?- subchars(frederica, Name, 4, 4).
     
     Name = "eric"
     

These predicates avoid constructing an atom that you may have no further use for.