Fri Jan 18 06:55:03 PST 2008 [EMAIL PROTECTED]
* Add quasi-quotation, courtesy of Geoffrey Mainland
This patch adds quasi-quotation, as described in
"Nice to be Quoted: Quasiquoting for Haskell"
(Geoffrey Mainland, Haskell Workshop 2007)
Implemented by Geoffrey and polished by Simon.
Overview
~~~~~~~~
The syntax for quasiquotation is very similar to the existing
Template haskell syntax:
[$q| stuff |]
where 'q' is the "quoter". This syntax differs from the paper, by using
a '$' rather than ':', to avoid clashing with parallel array comprehensions.
The "quoter" is a value of type Language.Haskell.TH.Quote.QuasiQuoter, which
contains two functions for quoting expressions and patterns, respectively.
quote = Language.Haskell.TH.Quote.QuasiQuoter quoteExp quotePat
quoteExp :: String -> Language.Haskell.TH.ExpQ
quotePat :: String -> Language.Haskell.TH.PatQ
TEXT is passed unmodified to the quoter. The context of the
quasiquotation statement determines which of the two quoters is
called: if the quasiquotation occurs in an expression context,
quoteExp is called, and if it occurs in a pattern context, quotePat
is called.
The result of running the quoter on its arguments is spliced into
the program using Template Haskell's existing mechanisms for
splicing in code. Note that although Template Haskell does not
support pattern brackets, with this patch binding occurrences of
variables in patterns are supported. Quoters must also obey the same
stage restrictions as Template Haskell; in particular, in this
example quote may not be defined in the module where it is used as a
quasiquoter, but must be imported from another module.
Points to notice
~~~~~~~~~~~~~~~~
* The whole thing is enabled with the flag -XQuasiQuotes
* There is an accompanying patch to the template-haskell library. This
involves one interface change:
currentModule :: Q String
is replaced by
location :: Q Loc
where Loc is a data type defined in TH.Syntax thus:
data Loc
= Loc { loc_filename :: String
, loc_package :: String
, loc_module :: String
, loc_start :: CharPos
, loc_end :: CharPos }
type CharPos = (Int, Int) -- Line and character position
So you get a lot more info from 'location' than from 'currentModule'.
The location you get is the location of the splice.
This works in Template Haskell too of course, and lets a TH program
generate much better error messages.
* There's also a new module in the template-haskell package called
Language.Haskell.TH.Quote, which contains support code for the
quasi-quoting feature.
* Quasi-quote splices are run *in the renamer* because they can build
*patterns* and hence the renamer needs to see the output of running the
splice. This involved a bit of rejigging in the renamer, especially
concerning the reporting of duplicate or shadowed names.
(In fact I found and removed a few calls to checkDupNames in RnSource
that are redundant, becuase top-level duplicate decls are handled in
RnNames.)
M ./compiler/basicTypes/RdrName.lhs -2 +5
M ./compiler/basicTypes/SrcLoc.lhs +5
M ./compiler/deSugar/DsMeta.hs -3 +17
M ./compiler/hsSyn/Convert.lhs -1 +8
M ./compiler/hsSyn/HsExpr.lhs +7
M ./compiler/hsSyn/HsPat.hi-boot-6 +2
M ./compiler/hsSyn/HsPat.lhs +19
M ./compiler/hsSyn/HsPat.lhs-boot -1 +4
M ./compiler/hsSyn/HsUtils.lhs +7
M ./compiler/main/DynFlags.hs +2
M ./compiler/parser/Lexer.x +43
M ./compiler/parser/Parser.y.pp +6
M ./compiler/parser/RdrHsSyn.lhs +1
M ./compiler/rename/RnBinds.lhs -3 +2
M ./compiler/rename/RnEnv.lhs -43 +47
M ./compiler/rename/RnExpr.lhs -2 +16
M ./compiler/rename/RnPat.lhs -13 +54
M ./compiler/rename/RnSource.lhs -21 +36
M ./compiler/typecheck/TcExpr.lhs +2
M ./compiler/typecheck/TcPat.lhs +3
M ./compiler/typecheck/TcRnMonad.lhs +3
M ./compiler/typecheck/TcRnTypes.lhs -2 +2
M ./compiler/typecheck/TcSplice.hi-boot-6 -1 +3
M ./compiler/typecheck/TcSplice.lhs -8 +101
M ./compiler/typecheck/TcSplice.lhs-boot -1 +5
M ./docs/users_guide/flags.xml +6
M ./docs/users_guide/glasgow_exts.xml +138
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