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Connor Olding 2016-11-27 21:49:46 -08:00
parent 63ddf558df
commit 635621de0d
1 changed files with 7 additions and 25 deletions
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NOTES.md
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@ -184,14 +184,13 @@ that Dumper can later understand.
the `:check` method
asserts that a token exists and is of a given type (`tt`).
it will defer to the `:lookup` method if the token type mismatches,
which isn't guaranteed to help.
preprocessing is split into three passes:
preprocessing is split into two passes:
### pass 1
resolves variables by substitution, parses expressions,
resolves variables by substitution,
parses and evaluates expressions,
and collects relative labels.
this pass starts by creating a new, empty table of statements to fill.
@ -200,11 +199,11 @@ statements are passed through, possibly modified, or read and left-out.
the reason for the copying is that taking indexes into an array (statements)
that you're removing elements from is A Bad Idea.
variable-declaring statements (`!VAR`) are read to a dictionary table,
for future replacement of their keys with values by the `:lookup` method.
all expression tokens are evaluated,
and all variable tokens are substituted.
note that the variable-parsing code itself calls `:lookup` through `:check`,
so new variables can simply copy the values of previous variables.
variable-declaring statements (`!VAR`) are read to a dictionary table
for future substitution of their keys with values.
labels (`!LABEL`) are checked for RELLABEL tokens to collect
for later replacement in pass 2.
@ -213,35 +212,18 @@ appended and prepended respectively.
the collection tables are arrays of tables containing the keys
`index` and `name`.
every statement that isn't eaten has its tokens looked-up by the
`:lookup` method. at this state, it just handles variable substitution.
### pass 2
resolves relative labels by substitution.
this code enables `self.do_labels` which tells `:lookup` to start
handling relative labels as well, now that they've all been collected.
`:lookup` is run on every token of every statement.
the appending/prepending done in pass 1 ensures
that the appropriate relative labels are found in the proper order.
### pass 3
attempts to parse and evaluate constant expressions.
### room for improvment
pass 3 (expressions) should be an attempt to evaluate constants,
and parsing should be moved to be part of pass 1.
looking back, the `new_statements` ordeal
only seems necessary for the (poor) error handling it provides.
the handling of statement tables could be made better.
## Expander
expands pseudo-instructions, including the inferrence of implied registers.