24 The Design Philosophy of POP-2 R.J. Popplestone

INTRODUCTION Pop-2 (Burstall & Popplestone, 1968) represents a fairly far-reaching revision, extension and systematization of the author's Pop-1 (Popplestone, 1968). The thoughts expressed here consequently represent a point of view elaborated jointly with my co-designer of Pop-2, Dr R. M. Burstall. AIMS POP-2 is a language to be implemented on real machines, using modest resources of manpower. An implementation of the language must be possible which permits large problems to be tackled. This implementation must not be too inefficient in its use of machine time, or too profligate in its use of store. The language must also take into account such properties of real machines as overwritable store--that is to say it must not be a purely constructive language: it must allow assignment. Pop-2 handles a large range of structures such as list cells (cf. CPO and records (called beads in AED).