A programming language and computer system adapted to receive and execute f-programs written in a programming language that provides a mechanism to sequence and check the correctness of the execution of a plurality of code segments. The method provides for sequencing the execution of p-segments by a computer processor, where each p-segment is a sequence of one or more executable statements. The p-segments may be part of a manipulation program. An f-program includes a number of f-segments. The manipulation program is configured so that after the completion of execution of each p-segment, control is passed to a specific f-segment associated with the completed p-segment, and at least one variable identifier and value of the variable computed by the completed p-segment is passed to the f-segment so that the f-segment either causes execution to terminate or passes control to one of the p-segments.