#1800: Template Haskell support for running functions defined in the same
module
---------------------------------+------------------------------------------
Reporter: simonpj | Owner:
Type: feature request | Status: new
Priority: normal | Milestone: _|_
Component: Template Haskell | Version: 6.6.1
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Os: Unknown | Testcase:
Architecture: Unknown |
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Comment (by guest):
It would be interesting to note how the template-haskell end user copes
with this problem to illustrate why the proposed feature is useful.
I myself have had to face this problem when designing an embedded compiler
for system design.
Doe to the mentioned limitation I'm normally forced to "push" the
arguments out of the splice.
As a (simplified) example, in my System Modelling DSL I have to create
system definition. That is done by providing the function Name together
with the identifiers of its inputs and outputs.
{{{
inputs = ["in1", "in2"]
outputs = ["out1", "out2"]
f :: Signal Int -> Signal Int -> (Signal Int, Signal Int)
f = ...
}}}
Since it is not possible to do
{{{
system :: SysDef
system = $(mkSysDef 'f inputs outputs)
}}}
due to the limitation explained in this ticket. I'm forced to do:
{{{
system :: SysDef
system = $(mkSysDef 'f) inputs outputs
-- where mkSysDef :: Name -> ExpQ
}}}
My solution does not solve the problem. It rather bypasses it.
Furthermore, mkSysDef unfortunately cannot do static checking (for
example, it cannot make sure that all the inputs and outputs have
different identifiers). However, that's better than asking the user to
create the system definitions and identifiers in different modules.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1800#comment:2>
GHC <http://www.haskell.org/ghc/>
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