haskell.md - #316
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…Hopper Ran the entire documented sequence verbatim on Hopper: module load ghcup -> ghcup install ghc 9.10.1 -> stack new matmul new-template -> edit app/Main.hs and package.yaml exactly as shown -> stack build. Found the real bug the doc had: stack manages its own GHC install, independent of ghcup, chosen by whatever the Stackage LTS snapshot resolver needs (currently ghc-9.10.3 for the snapshot stack new picks by default) - not whatever version was just installed with ghcup. The doc's ghcup step installs 9.10.1 but the sample find output showed ghc-9.6.5, a third, unrelated number. Added a note explaining stack/ghcup are independent here, and updated the find/run example paths to the version actually observed (ghc-9.10.3), noting this number will keep drifting as Stackage's default snapshot updates over time. The build succeeded and produced the exact 4x4 matrix output already documented, unchanged. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Ran the entire documented sequence live on Hopper, verbatim as written:
module load ghcup→ghcup install ghc 9.10.1→stack new matmul new-template→ editapp/Main.hsandpackage.yamlexactly as shown →stack build.Found and fixed the version inconsistency flagged for this file:
stackmanages its own GHC toolchain completely independently ofghcup. It picks whatever GHC the Stackage LTS snapshot resolver needs atstack newtime (currently resolves toghc-9.10.3) — not the version you just installed withghcup(9.10.1per the doc), and not the9.6.5an older revision of this doc showed either. All three numbers are/were real observations from different points in time, just not causally related the way the doc implied. Added an explicit note clarifying stack and ghcup are independent here, and corrected the examplefind/run paths to the version actually observed in this test run.Build succeeded and produced the exact 4×4 matrix output already documented — unchanged, confirmed working:
The
package.yamledit (adding- matrixunder thematmul-exeexecutable'sdependencies:) worked exactly as documented, no changes needed there.Test plan
module load ghcup+ghcup install ghc 9.10.1on Hopper — succeededstack new matmul new-template, editedMain.hs/package.yamlas documentedstack build— succeeded, confirmed actual GHC version used (9.10.3, via Stack's own resolver, independent of the ghcup install)