Code cleanup in generate stage

[JSAbrahams]

Split up the logic slightly more so the top-level generate function doesn't do too much besides calling other functions.

Some further code style improvements, such as using if guards where applicable in matches.

The following are no longer core constructs, but instead are generated using other constructs:

• Print, which can just be generated as a function call to print: print( ... )
• Dictionary, which is just an index call to a set: { ... }[ ...]
• DefaultDictionary, which is a function call with the default argument and set, and index call to the function call: defaultdict( ..., { ... })[ ...]

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (develop@2014071). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff             @@
##             develop     #291   +/-   ##
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  Coverage           ?   85.46%           
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  Files              ?       99           
  Lines              ?     9841           
  Branches           ?        0           
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  Hits               ?     8411           
  Misses             ?     1430           
  Partials           ?        0           

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