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78 lines
2.1 KiB
Idris
78 lines
2.1 KiB
Idris
module Main
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record Point where
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constructor MkPoint
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x : Double
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y : Double
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-- a record creates two projections:
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--
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-- .x : Point -> Double
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-- .y : Point -> Double
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--
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-- because %prefix_record_projections are on by default, we also get:
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--
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-- x : Point -> Double
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-- y : Point -> Double
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-- to prevent cluttering the ordinary name space with short identifiers
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%prefix_record_projections off
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record Rect where
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constructor MkRect
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topLeft : Point
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bottomRight : Point
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-- .topLeft : Rect -> Point
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-- .bottomRight : Rect -> Point
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--
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-- For Rect, we don't get the prefix projections:
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--
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-- Main> :t topLeft
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-- (interactive):1:4--1:11:Undefined name topLeft
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-- Main> :t .topLeft
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-- \{rec:0} => .topLeft rec : ?_ -> Point
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pt : Point
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pt = MkPoint 4.2 6.6
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rect : Rect
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rect =
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MkRect
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(MkPoint 1.1 2.5)
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(MkPoint 4.3 6.3)
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-- New lexical structure:
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--
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-- Foo.bar.baz with uppercase F is one lexeme: NSIdent ["baz", "bar", "Foo"]
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-- foo.bar.baz with lowercase f is three lexemes: foo, .bar, .baz
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-- .foo.bar.baz is three lexemes: .foo, .bar, .baz
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--
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-- If you want Constructor.field, you have to write (Constructor).field.
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--
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-- New syntax of simpleExpr:
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--
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-- Expressions binding tighter than application (simpleExpr),
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-- such as variables or parenthesised expressions,
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-- have been renamed to simplerExpr,
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-- and an extra layer of syntax has been inserted.
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--
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-- simpleExpr ::= (.field)+ -- parses as PRecordProjection
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-- | simplerExpr (.field)+ -- parses as PRecordFieldAccess
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-- | simplerExpr -- (parses as whatever it used to)
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--
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-- (.foo) is a name, so you can use it to e.g. define a function called .foo (see .squared below)
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-- (.foo.bar) is a parenthesised expression
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--
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-- New desugaring rules
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--
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-- (.field1 .field2 .field3) desugars to (\x => .field3 (.field2 (.field1 x)))
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-- (simpleExpr .field1 .field2 .field3) desugars to ((.field .field2 .field3) simpleExpr).
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--
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-- There are more details such as namespacing; see below.
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-- user-defined projections work, too (should they?)
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(.squared) : Double -> Double
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(.squared) x = x * x
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