Tangle -- The big output switch

In the previous part we saw that the token stream is turned into an output buffer + some state (basically a queue), by calling three functions send_out, send_val, and send_sign.

In this part we’ll see exactly when those three functions are called respectively (and with what arguments), i.e. the complex rules on what happens if Token X is followed by Token Y are all here.

The cases are:

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• 0: (do nothing)

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• [A-Za-z]: ident, 1

• IDENTIFIER: ident, k

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• [0-9]: scan number, sendval(n), if E goto get_fraction

• CHECK_SUM: sendval

• OCTAL: sendval

• HEX: sendval

• NUMBER: sendval

• .:

  • If followed by another ., then str, 2

  • If followed by [0-9], goto get_fraction

  • Followed by anything else: misc, .

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• +, -: sign

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• AND_SIGN: ident, 3

• NOT_SIGN: ident, 3

• IN: ident, 2

• OR: ident, 2

• LEFT_ARROW: ident, 2

• NOT_EQUAL: ident, 2

• <=

• >=

• ==

• ..

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• ': str, k

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• (other printable chars)

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• BEGIN_COMMENT

• END_COMMENT

• MODULE_NUMBER

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• JOIN

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• VERBATIM

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• FORCE_LINE

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• everything else is an error, as it’s an unprintable character

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The above is incomplete in details (just read the code below), and can probably be better presented as a table of: if you’ve just seen token X, and you see token Y, what should you do.