%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%  Dynamic semantics  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% The definitions in this file do *not* strictly correspond to any specific
% code in GHC. They are here to provide a reasonable operational semantic
% interpretation to the typing rules presented in the other ott files. Thus,
% your mileage may vary. In particular, there has been *no* attempt to
% write any formal proofs over these semantics.
%
% With that disclaimer disclaimed, these rules are a reasonable jumping-off
% point for an analysis of FC's operational semantics. If you don't want to
% worry about mutual recursion (and who does?), you can even drop the
% environment S.

grammar

defns
OpSem :: '' ::=

defn S |- e --> e'  ::  :: step :: 'S_' {{ com Single step semantics }}
{{ tex \begin{array}{l} [[S]] \labeledjudge{op} [[e]] [[-->]] [[e']] \end{array} }}
by

S(n) = e
----------------- :: Var
S |- n --> e

S |- e1 --> e1'
------------------- :: App
S |- e1 e2 --> e1' e2

----------------------------- :: Beta
S |- (\n.e1) e2 --> e1[n |-> e2]

g0 = sym (nth 0 g)
g1 = nth 1 g
not e2 is_a_type
not e2 is_a_coercion
----------------------------------------------- :: Push
S |- ((\n.e1) |> g) e2 --> (\n.e1 |> g1) (e2 |> g0)

---------------------------------------- :: TPush
S |- ((\n.e) |> g) t --> (\n.(e |> g n)) t

g0 = nth 1 (nth 0 g)
g1 = sym (nth 2 (nth 0 g))
g2 = nth 1 g
------------------------------- :: CPush
S |- ((\n.e) |> g) g' --> (\n.e |> g2) (g0 ; g' ; g1)

--------------------------------------- :: Trans
S |- (e |> g1) |> g2 --> e |> (g1 ; g2)

S |- e --> e'
------------------------ :: Cast
S |- e |> g --> e' |> g

S |- e --> e'
------------------------------ :: Tick
S |- e { tick } --> e' { tick }

S |- e --> e'
--------------------------------------- :: Case
S |- case e as n return t of </ alti // i /> --> case e' as n return t of </ alti // i />

altj = K </ alphabb_kbb // bb /> </ xcc_tcc // cc /> -> u
u' = u[n |-> e] </ [alphabb_kbb |-> sbb] // bb /> </ [xcc_tcc |-> ecc] // cc />
-------------------------------------------------------------- :: MatchData
S |- case K </ t'aa // aa /> </ sbb // bb /> </ ecc // cc /> as n return t of </ alti // i /> --> u'

altj = lit -> u
---------------------------------------------------------------- :: MatchLit
S |- case lit as n return t of </ alti // i /> --> u[n |-> lit]

altj = _ -> u
no other case matches
------------------------------------------------------------ :: MatchDefault
S |- case e as n return t of </ alti // i /> --> u[n |-> e]

T </ taa // aa /> ~#k T </ t'aa // aa /> = coercionKind g
forall </ alphaaa_kaa // aa />. forall </ betabb_k'bb // bb />. </ t1cc // cc /> @-> T </ alphaaa_kaa // aa /> = dataConRepType K
</ e'cc = ecc |> (t1cc @ </ [alphaaa_kaa |-> nth aa g] // aa /> </ [betabb_k'bb |-> <sbb>_Nom] // bb />) // cc />
--------------------------- :: CasePush
S |- case (K </ taa // aa /> </ sbb // bb /> </ ecc // cc />) |> g as n return t2 of </ alti // i /> --> \\ case K </ t'aa // aa /> </ sbb // bb /> </ e'cc // cc /> as n return t2 of </ alti // i />

----------------- :: LetNonRec
S |- let n = e1 in e2 --> e2[n |-> e1]

S, </ [ni |-> ei] // i /> |- u --> u'
------------------------------------ :: LetRec
S |- let rec </ ni = ei // i /> in u --> let rec </ ni = ei // i /> in u'

--------------- :: LetRecApp
S |- (let rec </ ni = ei // i /> in u) e' --> let rec </ ni = ei // i /> in (u e')

---------------- :: LetRecCast
S |- (let rec </ ni = ei // i /> in u) |> g --> let rec </ ni = ei // i /> in (u |> g)

--------------- :: LetRecCase
S |- case (let rec </ ni = ei // i /> in u) as n0 return t of </ altj // j /> --> \\ let rec </ ni = ei // i /> in (case u as n0 return t of </ altj // j />)

--------------- :: LetRecFlat
S |- let rec </ ni = ei // i /> in (let rec </ nj' = ej' // j /> in u) --> let rec </ ni = ei // i />;; </ nj' = ej' // j /> in u

fv(u) \inter </ ni // i /> = empty
--------------------------------- :: LetRecReturn
S |- let rec </ ni = ei // i /> in u --> u