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    I pointed out the use of the shunting yard algorithm in the original C compilers this post:

    http://www.oilshell.org/blog/2017/04/22.html

    Code:

    http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/source/c/c01.c

    If you compare it to the first c01.c you can see they are related, i.e. build() which is a silly name by modern standards. But the code got way more readable! I guess there was no preprocessor at first, so they did stuff like “case 8: … case 9: … case 36: …”