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Document how to iterate on changes to template desugaring (#3663)

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Moritz Kiefer 2019-11-28 16:33:24 +01:00 committed by GitHub
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ghc-lib/working-on-ghc-lib.md
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@ -66,6 +66,33 @@ stack build --stack-yaml=hadrian/stack.yaml --only-dependencies
hadrian/build.stack.sh --configure --flavour=quickest -j
```
## Iterating on Template Desugaring
Modifying GHC, building `ghc-lib` and then building `damlc` is quite time
intensive and makes mistakes very costly. Therefore it is usually preferable to
first take a look at the new output from template desugaring before building `ghc-lib`.
The fastest option for that is to build GHC with
```
./hadrian/build.sh -j --flavour=quickest --freeze1
```
You can then run GHC on a DAML file as follows
```
./_build/stage1/bin/ghc ~/tmp/Test.hs -ddump-parsed
```
Note that the file should end with `.hs`, otherwise GHC will think that it is an additional input
for the linking phase and your DAML file should start with:
```
{-# LANGUAGE DamlSyntax #-}
```
You will get compile errors after the parse tree has been emitted since the standard library is missing
but if you just want to see the output from template desugaring, this is sufficient.
## How to build `ghc-lib` from the DA GHC fork
(You don't need to follow the previous step in order to do this.)