Emulators and interpreters in Fortran

The early Prolog implementations were bootstrapped using Fortran:

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From June to the end of the year [1973], Gérard Battani, Henri Meloni, and Rent Bazzoli, postgraduate students at the time, wrote the interpreter in FORTRAN and its supervisor in Prolog

Some of the very early Lisp environments were implement in ancient dialects of Fortran:

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This paper concentrates on the development of the basic ideas of LISP and distinguishes two periods - Summer 1956 through Summer 1958 when most of the key ideas were developed (some of which were implemented in the FORTRAN based FLPL), and Fall 1958 through 1962 when the programming language was implemented and applied to problems of artificial intelligence. After 1962, the development of LISP became multi-stranded, and different ideas were pursued in different places.

Slightly related, I see this as my ideal computing environment, with Fortran, C, or C++ being used for performance critical areas.

Marsh, B. D., Williams, T. M., & Mathieson, G. L. (1990). The Use of Mixed Prolog/Fortran for Battle Simulation. The Journal of the Operational Research Society, 41(4), 311–318. The Use of Mixed Prolog/Fortran for Battle Simulation on JSTOR

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A mixed-system architecture is developed, in which Fortran and Prolog are each used to best advantage, and which allows discrete events to be combined with pseudo-continuous processes. The architecture is analysed in terms of a number of performance metrics. The paper concludes that the mixed architecture is feasible, practicable and brings a variety of benefits.