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repl: Introduce :defs and :t <identifier> commands#9755

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lukasjuhrich wants to merge 7 commits into
roc-lang:mainfrom
lukasjuhrich:repl/def-and-t
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repl: Introduce :defs and :t <identifier> commands#9755
lukasjuhrich wants to merge 7 commits into
roc-lang:mainfrom
lukasjuhrich:repl/def-and-t

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@lukasjuhrich

@lukasjuhrich lukasjuhrich commented Jun 22, 2026 •
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This is me elaborating on an idea I had in #ideas > Print type in `roc repl`, so feel free to discuss/reject/defer API decisions.

What was added

The repl can now

  • print the type of top-level definitions by name using :t <identifier>, like ghci can
  • print all definitions using the :defs command

It looks like this:
image

Note that :t is the actual feature I care about and :defs was the way to get me there. but I still think it is useful.
Feel free to reject this PR or parts of it or discuss naming / formatting. I'm happy to start a discussion over at zulip.

What was not added

  • general command dispatching whenever the line starts with :
  • allowing arbitrary expressions to be typed in after :t (which would not be too hard I think)
  • Tests (what should they look like? interpreter state is not changed here so it's a bit different from the rest)

AI usage disclaimer

  • No vibe coding
  • some chat assistance with the zig stdlib and questions about how to write zig code more idiomatically.

All mistakes are my own, so feel free to tell me what I did wrong.

@lukasjuhrich
feat(repl): Add a :defs command
f232a67
@lukasjuhrich
Look up and print inferred types as well
e074209
@lukasjuhrich
refactor(repl): Extract ReplSession.initParsedResources
6cad213
@lukasjuhrich
feat(repl): Add :t type printing command
0659759
@lukasjuhrich
refactor(repl): rename output→out
7db93c6
@lukasjuhrich
feat(repl): Consolidate :defs styling
0ae49db 
This consistently applies two rules:

- user-provided information is normal,
  additional hints dim
- let-bindings are upright, everything else in
  italics  

Also, defs are separated by a newline except for
annotations, because usually they are directly
followed by the let-binding they belong to.
@lukasjuhrich
Include new commands in help text
3721bcb
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@lukasjuhrich