PURPOSE:To attain a fast execution of a prolog processing system of an instruction system which operates exclusively a variable by using a sorting means that decides whether the variable should be allocated to a register or a memory. CONSTITUTION:For a prolog program A10, a sentence structure is analyzed through the sentence structure analysis A20 of a prolog compiler A and an intermediate word IA30 is outputted. The word IA30 is supplied to a logic variable sorting means A40. This means A40 contains a detecting means A410 for continuous execution part of clause and an identifying means A420 which identifies the variable emerging at the continuous execution part only in order to sort and set the register variables based on the gathering of incorporated predicates having a high emerging frequency and small processing load. The means A40 outputs an intermediate word IIA50 in response to the sorted variables. For such a word IIA50, an object program A70 containing a train of instruction codes is produced and outputted through the code production A60.
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