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base repository: pfalcon/python-compiler.old
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compare: for-block-scope
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  • 3 commits
  • 6 files changed
  • 1 contributor

Commits on Nov 29, 2020

  1. symbols: Basic block-level scoping infrastructure. 

    We introduce BlockScope, as a subclass of FunctionScope, to piggyback on
*some* of the scoping processing done for FunctionScope (but we otherwise
going to ignore the rest of it).

What we mostly need BlockScope for is like a container for remappings of
var_name -> var_name.NN (numeric counter). We'd like to apply remapping
"on the fly" (vs a separate pass on AST with explicit variable rewriting).
The mapping is stored in Scope.defs (which previously was set emulated
using dict, i.e. contained 1 as a value).

For the rest of functionality, we try to forward it to the containing
function scope (and for this, we maintain .func_parent pointer in BlockScope,
note that it maybe also module or class scope).
    @pfalcon
    pfalcon committed Nov 29, 2020
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  2. symbols, pycodegen: Prototype of block-level scope for "for" variables. 

    Due to the fact that this package doesn't include tokenizer and AST parser,
this prototype applies block-level scope to all "for" statements, whereas
the original proposal is to apply it only to the loops of new "for const"
syntax. This prototype also explores block-level scope aspect, not the
constness aspect.

The implementation is based on basic block-level scoping support introduced
in the previous commit.

The only interesting part here is that we actually have to walk BlockScope
subtree to (potentially) remap block-scope variable names. The original
inspriring idea was to avoid scope-iteration at all, but we clearly don't
do enough processing in symbols.py for that. And note that to achieve that,
we'd need to duplicate mapping information in different scopes, i.e. would
achieve O(1) lookups, but at the price of additional memory usage (likely,
quadratic). OTOH, due to processing already done by symbols.py, we already
have sparse namespacing info (comparing to the original AST), and in most
cases, the scope tree will be rather shallow (or put it differently, price
of O(n) compile-time lookups will be paid only by the code which (ab)uses
nested scopes too much).
    @pfalcon
    pfalcon committed Nov 29, 2020
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  3. example_for*.py: Example for "for" block-level scope.

    @pfalcon
    pfalcon committed Nov 29, 2020
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