diff options
Diffstat (limited to 'compiler/GHC/Hs/Expr.hs')
| -rw-r--r-- | compiler/GHC/Hs/Expr.hs | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/compiler/GHC/Hs/Expr.hs b/compiler/GHC/Hs/Expr.hs index 72ac021e45..24b8247b32 100644 --- a/compiler/GHC/Hs/Expr.hs +++ b/compiler/GHC/Hs/Expr.hs @@ -889,8 +889,9 @@ instance Outputable (HsPragE (GhcPass p)) where {- Note [Rebindable syntax and HsExpansion] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We implement rebindable syntax (RS) support by performing a desugaring -in the renamer. We transform GhcPs expressions affected by RS into the -appropriate desugared form, but **annotated with the original expression**. +in the renamer. We transform GhcPs expressions and patterns affected by +RS into the appropriate desugared form, but **annotated with the original +expression/pattern**. Let us consider a piece of code like: @@ -981,18 +982,24 @@ tcl_in_gen_code Bool to False. --- +An overview of the constructs that are desugared in this way is laid out in +Note [Handling overloaded and rebindable constructs] in GHC.Rename.Expr. + A general recipe to follow this approach for new constructs could go as follows: - Remove any GhcRn-time SyntaxExpr extensions to the relevant constructor for your construct, in HsExpr or related syntax data types. - At renaming-time: - take your original node of interest (HsIf above) - - rename its subexpressions (condition, true branch, false branch above) + - rename its subexpressions/subpatterns (condition and true/false + branches above) - construct the suitable "rebound"-and-renamed result (ifThenElse call above), where the 'SrcSpan' attached to any _fabricated node_ (the HsVar/HsApp nodes, above) is set to 'generatedSrcSpan' - take both the original node and that rebound-and-renamed result and wrap - them in an XExpr: XExpr (HsExpanded <original node> <desugared>) + them into an expansion construct: + for expressions, XExpr (HsExpanded <original node> <desugared>) + for patterns, XPat (HsPatExpanded <original node> <desugared>) - At typechecking-time: - remove any logic that was previously dealing with your rebindable construct, typically involving [tc]SyntaxOp, SyntaxExpr and friends. |