Module

Puppy.Runtime.Value

Package: purescript-puppy-runtime
Repository: katsujukou/purescript-puppy-runtime

The box a generated parser keeps its semantic values in.

A parser stack holds values of every type the grammar produces, so the driver cannot be told what is on it. Value is what it is told instead: an opaque type it only ever moves around.

The coercions are unsound on their own, and that is the point of this module -- there are exactly two of them, they sit here, and generated code never mentions Unsafe.Coerce itself. What makes them safe in practice is that a value is only ever unboxed at the position it was boxed at: the grammar fixes which production puts a value on the stack and which one takes it off, and the generator emits both halves from the same place.

#Value Source

data Value

#box Source

box :: forall a. a -> Value

#unbox Source

unbox :: forall a. Value -> a

#slot Source

slot :: Int -> Array Value -> Value

One of the values a production is reducing over.

The driver hands a semantic action exactly as many values as the production has symbols, so an index the generator emitted can only be out of range if the tables and the actions disagree -- which is a bug in the generator, not something a grammar can cause.

#internalError Source

internalError :: forall a. String -> a

Something the generator promised would not happen.

Reserved for broken tables. Nothing a grammar or an input can do should reach one of these; a parse error is an Either, not a crash.

Modules: Puppy.Runtime; Puppy.Runtime.Deps; Puppy.Runtime.Driver; Puppy.Runtime.Source; Puppy.Runtime.Value