See inferred types in complex OCaml code

Question

I'm a OCaml newbie working with some pretty complex (at least for me) OCaml code I didn't write. It would help a lot to understand it if I could see the inferred types for some of the values, as I can do with F# and Visual Studio by hovering over any value, e.g.:

F# showing inferred type

(screenshot borrowed from http://theburningmonk.com/2010/01/learning-f-part-1/)

I guess I could break down the code and feed it to the toplevel to get the types, but is there any other, simpler way?

score 8 · Accepted Answer · answered May 12 '11 at 17:09

8

First, you must compile your file (foo.ml) with the -annot flag. This generates the annotation file (foo.annot) that contains type information about all identifiers inside. You can include this as part of your makefile or build process.

Then, you need to rely on your IDE to display that information. I do this in Tuareg (the emacs mode) using Ctrl+C, Ctrl+T, which highlights the current expression and displays its type.

answered May 12 '11 at 17:09

Victor Nicollet

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You can also check https://github.com/avsm/ocaml-annot for a simple command line tool. – nimrodm May 12 '11 at 17:10
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ocaml-spotter extends -annot further, http://jun.furuse.info/hacks/ocamlspotter . – nlucaroni May 12 '11 at 17:22
Key sequence for vim with ocaml ftplugin is `t` (usually `,t`) – ygrek May 13 '11 at 06:41
@ygrek: why not add ftplugin as another answer? – Mauricio Scheffer May 13 '11 at 13:05
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real answer is to generate .annot files and editor is merely using them – ygrek May 13 '11 at 15:30

score 7 · Answer 2 · answered May 12 '11 at 17:52

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OcaIDE which is an O'Caml plug-in for Eclipse displays the inferred types on the fly while editing your code.

Example:

enter image description here

answered May 12 '11 at 17:52

0xFF

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score 1 · Answer 3 · answered May 12 '11 at 17:07

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You could enter the code into the ocaml toplevel. Yeah, it's not as pretty, but it'll show the types.

answered May 12 '11 at 17:07

aneccodeal

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yes, I know I could do this, but it's pretty complex code, it would be quite time-consuming to break down the code enough to get to the types I want to see. – Mauricio Scheffer May 12 '11 at 17:29
Toplevel + rlwrap is quite usable, if only there was a way to [save it](http://stackoverflow.com/questions/3966925/saving-my-running-toplevel-for-later)... – Gaius May 18 '11 at 15:16

score 1 · Answer 4 · answered May 12 '11 at 20:59

What works for me when reading OCaml code is to begin with the .mli files to see what the overall structure of the project is. From there, and having an idea of what are the dependencies, you can explore from the toplevel.

Alternatively, you can ocamlc -i the file in question for an overview of all the declared types and values, or use Tuareg mode in Emacs as replied elsewhere, if you are of that persuasion.

See inferred types in complex OCaml code

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