CakeML/cakeml

Add word shifts to basis

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#274 opened on May 3, 2017

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 (3 comments) (0 reactions) (1 assignee)Standard ML (98 forks)auto 404
enhancementhelp wanted

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Description

Currently, the basis library doesn't include any shift operations in the Word8 or Word64 modules, and the parser can't generate Opapps with a Shift operation. Thus, the user cannot write programs that shift words in the surface syntax.

Ideally, we'd like to add >> and << as 2 argument CakeML functions, but the Shift op is a unary op with the amount to shift built into the operator. We either need to make Shift a binary op, or we have to add a restricted form of shifting where >> is defined in the basis as a function of two arguments that does a case split on the 2nd to pick out which Shift to actually do.

Contributor guide

Research direction
Investigate the current implementation of shift operators in the basis library and the parser. Examine how Shift op is currently defined as a unary op. Decide between two approaches: (1) Make Shift a binary op, requiring changes to the op definition, parser, and semantics. (2) Add a restricted form of shifting by defining >> and << as functions in the basis that case split on the second argument to select the appropriate Shift operation. Implement the chosen approach and add corresponding tests.
Tech stack
None
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65