PLC-lang/rusty

Improved Method/Function value return syntax

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#1,094 opened on Feb 13, 2024

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enhancementgood first issue

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Description

The IEC 61131-3 Syntax for the returned Value from a Method or Function isn't very readable.

The syntax is *functionName* := *Value to Return*

I was actually trying to find the section of IEC 61131-3 that requires this syntax, but I can't seem to find it. I found code examples in the standard that use it, though. Could someone point me to it? I have a copy of the 3rd edition.

My proposal is an alternate syntax that is in line with almost all other modern languages. The system uses "return" as an alias over the function name. This ideal would be an optional syntax to maintain compatibility. return := *value to return*

FUNCTION mySumFunc : DINT
VAR_INPUT
    Blah_Blah1 : DINT;
    Blah_Blah2 : DINT;
VAR_END
return := Blah_Blah1 + Blah_Blah2;
END FUNCTION

This, I think, is much more readable and will also help with implementing Properties. (I will create another feature request for Properties)

Edit:

The new proposed syntax is the following with no := operator

VAR_INPUT
    Blah_Blah1 : DINT;
    Blah_Blah2 : DINT;
VAR_END
  RETURN Blah_Blah1 + Blah_Blah2; 
END FUNCTION```

Contributor guide

Research direction
Review the grammar definition for functions/methods in the parser to understand current return value syntax. Implement an alternative return statement syntax that assigns to 'return' or uses 'RETURN' without the assignment operator. Ensure compatibility with existing syntax. Update lexer, parser, and code generation accordingly.
Tech stack
rust
Domain
compilersbackend
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.
Half day
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Rustcompiler design
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30