Writing Compilers
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the reality
has many useful levels of abstraction, and in my opinion it's quite important to have at least passing familiarity with every level below the one you spend most of your time working at, so you get at least some idea where the leaks are going to spring.
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Some people like to call those symbols by other names, such as “characters”, “words”, “numbers”, “identifiers”, etc., but the reality's just symbols.
I'm also quite strongly inclined to put numbers and general symbols at the same abstraction level, rather than conceptually interposing a symbols level between numbers and bits.
