Hello, I am completely new to OCaml, and trying to set up OCaml Platform for VSCode. However, I keep on getting the error:
Failed to start the language server. “ocaml-lsp-server” is not installed in the current sandbox.
even though it appears that it should be installed, based on the extension sidebar. I have attached a screenshot of this, which seems to show that default is the selected sandbox, and that ocaml-lsp-server isinstalled. Whenever I do OCaml: Restart Language Server, I keep on getting the error.
# Packages matching: installed
# Name # Installed # Synopsis
astring 0.8.5 Alternative String module for OCaml
async v0.17.0 Monadic concurrency library
async_kernel v0.17.0 Monadic concurrency library
async_log v0.17.0 Logging library built on top of Async_unix
async_rpc_kernel v0.17.0 Platform-independent core of Async RPC library
async_unix v0.17.0 Monadic concurrency library
base v0.17.3 Full standard library replacement for OCaml
base-bigarray base
base-bytes base Bytes library distributed with the OCaml compiler
base-domains base
base-effects base
base-nnp base Naked pointers prohibited in the OCaml heap
base-threads base
base-unix base
base_bigstring v0.17.0 String type based on [Bigarray], for use in I/O and C-bindings
base_quickcheck v0.17.1 Randomized testing framework, designed for compatibility with Base
bin_prot v0.17.0-1 A binary protocol generator
camlp-streams 5.0.1 The Stream and Genlex libraries for use with Camlp4 and Camlp5
capitalization v0.17.0 Defines case conventions and functions to rename identifiers according to them
chrome-trace 3.20.2 Chrome trace event generation library
cmdliner 2.1.0 Declarative definition of command line interfaces for OCaml
core v0.17.1 Industrial strength alternative to OCaml's standard library
core_bench v0.17.0 Benchmarking library
core_extended v0.17.0 Extra components that are not as closely vetted or as stable as Core
core_kernel v0.17.0 Industrial strength alternative to OCaml's standard library
core_unix v0.17.1 Unix-specific portions of Core
cppo 1.8.0 Code preprocessor like cpp for OCaml
csexp 1.5.2 Parsing and printing of S-expressions in Canonical form
cstruct 6.2.0 Access C-like structures directly from OCaml
delimited_parsing v0.17.0 Parsing of character (e.g., comma) separated and fixed-width values
dune 3.20.2 Fast, portable, and opinionated build system
dune-build-info 3.20.2 Embed build information inside executable
dune-configurator 3.20.2 Helper library for gathering system configuration
dune-rpc 3.20.2 Communicate with dune using rpc
dyn 3.20.2 Dynamic type
either 1.0.0 Compatibility Either module
expect_test_helpers_core v0.17.0 Helpers for writing expectation tests
fiber 3.7.0 Dune's monadic structured concurrency library
fieldslib v0.17.0 Syntax extension to define first class values representing record fields, to g
fix 20250919 Algorithmic building blocks for memoization, recursion, and more
fmt 0.11.0 OCaml Format pretty-printer combinators
fpath 0.7.3 File system paths for OCaml
gel v0.17.0 A library to mark non-record fields global.
int_repr v0.17.0 Integers of various widths
jane-street-headers v0.17.0 Jane Street C header files
jsonrpc 1.25.0 Jsonrpc protocol implementation
jst-config v0.17.0 Compile-time configuration for Jane Street libraries
lambda-term 3.3.2 Terminal manipulation library for OCaml
logs 0.10.0 Logging infrastructure for OCaml
lsp 1.25.0 LSP protocol implementation in OCaml
lwt 5.9.2 Promises and event-driven I/O
lwt_react 1.2.0 Helpers for using React with Lwt
menhir 20250912 An LR(1) parser generator
menhirCST 20250912 Runtime support library for unparsers generated by Menhir
menhirLib 20250912 Runtime support library for parsers generated by Menhir
menhirSdk 20250912 Compile-time library for auxiliary tools related to Menhir
merlin-lib 5.6-504 Merlin's libraries
mew 0.1.0 Modal editing witch
mew_vi 0.5.0 Modal editing witch, VI interpreter
num 1.6 The legacy Num library for arbitrary-precision integer and rational arithmetic
ocaml 5.4.0 The OCaml compiler (virtual package)
ocaml-base-compiler 5.4.0 Official release of OCaml 5.4.0
ocaml-compiler 5.4.0 Official release of OCaml 5.4.0
ocaml-compiler-libs v0.17.0 OCaml compiler libraries repackaged
ocaml-config 3 OCaml Switch Configuration
ocaml-index 5.6-504 A tool that indexes value usages from cmt files
ocaml-lsp-server 1.25.0 pinned to version 1.25.0 at git+https://github.com/ocaml/ocaml-lsp.git
ocaml-options-vanilla 1 Ensure that OCaml is compiled with no special options enabled
ocaml-version 4.0.3 Manipulate, parse and generate OCaml compiler version strings
ocaml_intrinsics_kernel v0.17.1 Intrinsics
ocamlbuild 0.16.1 OCamlbuild is a build system with builtin rules to easily build most OCaml pro
ocamlc-loc 3.20.2 Parse ocaml compiler output into structured form
ocamlfind 1.9.8 A library manager for OCaml
ocamlformat 0.28.1 Auto-formatter for OCaml code
ocamlformat-lib 0.28.1 OCaml Code Formatter
ocamlformat-rpc-lib 0.28.1 Auto-formatter for OCaml code (RPC mode)
ocp-indent 1.9.0 A simple tool to indent OCaml programs
ocplib-endian 1.2 Optimised functions to read and write int16/32/64 from strings and bigarrays
ordering 3.20.2 Element ordering
parsexp v0.17.0 S-expression parsing library
pp 2.0.0 Pretty-printing library
ppx_assert v0.17.0 Assert-like extension nodes that raise useful errors on failure
ppx_base v0.17.0 Base set of ppx rewriters
ppx_bench v0.17.1 Syntax extension for writing in-line benchmarks in ocaml code
ppx_bin_prot v0.17.1 Generation of bin_prot readers and writers from types
ppx_cold v0.17.0 Expands [@cold] into [@inline never][@specialise never][@local never]
ppx_compare v0.17.0 Generation of comparison functions from types
ppx_custom_printf v0.17.0 Printf-style format-strings for user-defined string conversion
ppx_derivers 1.2.1 Shared [@@deriving] plugin registry
ppx_diff v0.17.1 A PPX rewriter that genreates the implementation of [Ldiffable.S].
ppx_disable_unused_warnings v0.17.0 Expands [@disable_unused_warnings] into [@warning "-20-26-32-33-34-35-36-37-38
ppx_enumerate v0.17.0 Generate a list containing all values of a finite type
ppx_expect v0.17.3 Cram like framework for OCaml
ppx_fields_conv v0.17.0 Generation of accessor and iteration functions for ocaml records
ppx_fixed_literal v0.17.0 Simpler notation for fixed point literals
ppx_globalize v0.17.2 A ppx rewriter that generates functions to copy local values to the global hea
ppx_hash v0.17.0 A ppx rewriter that generates hash functions from type expressions and definit
ppx_here v0.17.0 Expands [%here] into its location
ppx_ignore_instrumentation v0.17.0 Ignore Jane Street specific instrumentation extensions
ppx_inline_test v0.17.1 Syntax extension for writing in-line tests in ocaml code
ppx_jane v0.17.0 Standard Jane Street ppx rewriters
ppx_let v0.17.1 Monadic let-bindings
ppx_log v0.17.0 Ppx_sexp_message-like extension nodes for lazily rendering log messages
ppx_module_timer v0.17.0 Ppx rewriter that records top-level module startup times
ppx_optcomp v0.17.1 Optional compilation for OCaml
ppx_optional v0.17.0 Pattern matching on flat options
ppx_pipebang v0.17.0 A ppx rewriter that inlines reverse application operators `|>` and `|!`
ppx_sexp_conv v0.17.1 [@@deriving] plugin to generate S-expression conversion functions
ppx_sexp_message v0.17.0 A ppx rewriter for easy construction of s-expressions
ppx_sexp_value v0.17.0 A ppx rewriter that simplifies building s-expressions from ocaml values
ppx_stable v0.17.1 Stable types conversions generator
ppx_stable_witness v0.17.0 Ppx extension for deriving a witness that a type is intended to be stable. In
ppx_string v0.17.0 Ppx extension for string interpolation
ppx_string_conv v0.17.0 Ppx extension for generating of_string & to_string
ppx_tydi v0.17.1 Let expressions, inferring pattern type from expression.
ppx_typerep_conv v0.17.1 Generation of runtime types from type declarations
ppx_variants_conv v0.17.1 Generation of accessor and iteration functions for ocaml variant types
ppx_yojson_conv_lib v0.17.0 Runtime lib for ppx_yojson_conv
ppxlib 0.37.0 Standard infrastructure for ppx rewriters
ppxlib_jane v0.17.4 Utilities for working with Jane Street AST constructs
protocol_version_header v0.17.0 Protocol versioning
re 1.14.0 RE is a regular expression library for OCaml
react 1.2.2 Declarative events and signals for OCaml
record_builder v0.17.0 A library which provides traversal of records with an applicative
result 1.5 Compatibility Result module
sexp_pretty v0.17.0 S-expression pretty-printer
sexplib v0.17.0 Library for serializing OCaml values to and from S-expressions
sexplib0 v0.17.0 Library containing the definition of S-expressions and some base converters
spawn v0.17.0 Spawning sub-processes
splittable_random v0.17.0 PRNG that can be split into independent streams
stdio v0.17.0 Standard IO library for OCaml
stdlib-shims 0.3.0 Backport some of the new stdlib features to older compiler
stdune 3.20.2 Dune's unstable standard library
textutils v0.17.0 Text output utilities
time_now v0.17.0 Reports the current time
timezone v0.17.0 Time-zone handling
topkg 1.1.1 The transitory OCaml software packager
trie 1.0.0 Strict impure trie tree
typerep v0.17.1 Typerep is a library for runtime types
uchar 0.0.2 Compatibility library for OCaml's Uchar module
uopt v0.17.0 An [option]-like type that incurs no allocation, without requiring a reserved
utop 2.16.0 Universal toplevel for OCaml
uucp 17.0.0 Unicode character properties for OCaml
uuseg 17.0.0 Unicode text segmentation for OCaml
uutf 1.0.4 Non-blocking streaming Unicode codec for OCaml
variantslib v0.17.0 Part of Jane Street's Core library
xdg 3.20.2 XDG Base Directory Specification
yojson 3.0.0 Yojson is an optimized parsing and printing library for the JSON format
zed 3.2.3 Abstract engine for text edition in OCaml
I have installed VSCode to try to reproduce your issue to help you:
1. I can reproduce your issue when VSCode is installed using Flatpak 2. Everything is working fine when I installed VSCode via package manager (or just downloading in my case .deb from VSCode webpage).
Can you confirm if you installed VSCode via Flatpak or similar to narrow possible reasons for your issue?
Thanks everyone for the help, looks like I managed to figure out the issue.
Previously, I had a project open which was simply just a copy of the example in the guided tour in Real World OCaml. It seems like while having this project open, the OCaml Platform extension wasn’t working. However, when starting a new project with dune init proj, looks like it works.
Does anyone know why it wasn’t working before? I’m guessing there was something weird that I did in the previous project that threw off the extension. But this seems more like a bug in the extension than something specifically that I did?
