1. In a method of data processing in a processor programmable in a symbolic programming language of the type including LISP and having automatic memory reclamation, wherein the processor repeatedly applies address words to gain memory to write data structures into main memory and read data structures from main memory to perform operations thereon, and the processor allocates previously used portions of main memory for writing data structures by reclaiming same, the improvement wherein the step of reclaiming comprises: a. defining address regions in main memory including a main space and a relatively smaller subsidiary space; b. writing new data structures into subsidiary space until it is full; and c. reclaiming subsidiary space when it is full by i. detecting the writing of a data structure into main space having a pointe into subsidiary space; ii. adding memory locations of pointer detected in step (i) to a given data structure; iii. halting operation of the processor; iv. locating all pointers to subsidiary space by referencing the given data structure; v. locating useful data structures in subsidiary space from the pointers located in step (iv) and; vi. copying the located useful data structures into main space until there are no further pointers into subsidiary space.