#4316: Interactive "do" notation in GHCi
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Reporter: mitar | Owner: vivian
Type: feature request | Status: patch
Priority: normal | Milestone: 7.2.1
Component: GHCi | Version: 6.12.3
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by simonmar):
The basic idea is this: when we get a line of input from the user, we call
the lexer in "alternative layout rule mode" to read tokens up to the end
of the line, and then inspect the state of the lexer at that point. The
alternative layout rule tracks layout contexts and brackets, so we can
tell whether the current line is finished or not. Then we read the next
line, start lexing it using the state from the previous line, and so on.
If we get a blank line, finish and parse the input as usual.
I haven't thought through all the details here, but I think the idea is
very cool: GHC will be able to tell automatically whether the input is
complete or not by counting brackets. One disadvantage is, as you point
out, a `let` binding would require a double-return to terminate it. So
perhaps this automatic multi-line input could be optional, but I imagine
people would get used to it pretty quickly.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4316#comment:14>
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