B-Lang-org/bsc

Syntax for enum encodings in BH/Classic

Open

#292 opened on Jan 14, 2021

View on GitHub
 (0 comments) (0 reactions) (0 assignees)Haskell (1,108 stars) (178 forks)batch import
good first issue

Description

BSV allows the user to specify a custom encoding for the derived Bits of an enum. For example, from bsc.bluetcl/commands/Test.bsv in the testsuite:

typedef enum { Red2 = 1, Yellow2, Blue2 } BarSet deriving(Bits);

This is handled by pEnumTag in Parser/BSV/CVParser.lhs (where it fills in the fields like cos_tag_encoding). In the BH/Classic parser (Parser/Classic/CParser.hs) the function pDataB just fills in integers starting from zero ([0..]).

It might be worth creating a BH/Classic syntax for specifying a custom encoding. (It could perhaps be an attribute, if that's easier.) This is part of the larger issue that BSV was the only supported syntax for a long time, so there are some things that can be specified in that syntax but not in BH/Classic. See, for example, issue #224. I don't personally have a need for custom encodings in BH/Classic, but I thought it was worth recording the difference in the Issues database. (Should we have an open Issue for listing all of the known differences? or perhaps this a good use for the new Discussions area?)

Implementing the syntax should be simple, so I'm tagging this as a "good first issue", but we'd need to decide on the syntax first.

Contributor guide

Tech stack
None
Domain
tooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Knowledge of BH/Classic syntaxFamiliarity with BSC parser
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
The issue is about adding custom enum encoding syntax to the BH/Classic parser. The implementation would likely involve modifying the `pDataB` function in `Parser/Classic/CParser.hs` to support user specified tag encodings, similar to how it is done in `pEnumTag` in `Parser/BSV/CVParser.lhs`. Before implementing, the community needs to decide on the syntax, possibly using an attribute. The issue is open and available for contribution.