From 5471af45fd04169eb184371dcd8f791e507eab6f Mon Sep 17 00:00:00 2001
From: Alasdair Armstrong
Date: Wed, 24 Oct 2018 17:25:47 +0100
Subject: Add constraint synonyms

Currently not enabled by default, the flag -Xconstraint_synonyms
enables them

For generating constraints in ASL parser, we want to be able to give
names to the constraints that we attach to certain variables. It's
slightly awkward right now when constraints get long complicated
because the entire constraint always has to be typed out in full
whenever it appears, and there's no way to abstract away from that.

This adds constraint synonyms, which work much like type synonyms
except for constraints, e.g.

constraint Size('n) = 'n in {1, 2, 4, 8} | 128 <= 'n <= 256

these constraints can then be used instead of the full constraint, e.g.

val f : forall 'n, where Size('n). int('n) -> unit

Unfortunatly we need to have a keyword to 'call' the constraint
synonym otherwise the grammer stops being LR(1). This could be
resolved by parsing all constraints into Parse_ast.atyp and then
de-sugaring them into constraints, which is what happens for
n-expressions already, but that would require quite a bit of work on
the parser.

To avoid this forcing changes to any other parts of Sail, the intended
invariant is that all constraints appearing anywhere in a type-checked
AST have no constraint synonyms, so they don't have to worry about
matching on NC_app, or calling Env.expand_typquant_synonyms (which
isn't even exported for this reason).
---
 language/sail.ott | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

(limited to 'language/sail.ott')

diff --git a/language/sail.ott b/language/sail.ott
index 2edffcbe..59d51d68 100644
--- a/language/sail.ott
+++ b/language/sail.ott
@@ -293,6 +293,7 @@ n_constraint :: 'NC_' ::=
   | kid 'IN' { num1 , ... , numn }              :: :: set
   | n_constraint \/ n_constraint'               :: :: or
   | n_constraint /\ n_constraint'               :: :: and
+  | id ( nexp1 , ... , nexpn )                  :: :: app
   | true                                        :: :: true
   | false                                       :: :: false
 
@@ -1012,29 +1013,30 @@ prec :: '' ::=
 def :: 'DEF_' ::=
   {{ com top-level definition }}
   {{ auxparam 'a }}
-  | kind_def                                         :: :: kind
+  | kind_def                                           :: :: kind
     {{ com definition of named kind identifiers }}
-  | type_def                                         :: :: type
+  | type_def                                           :: :: type
     {{ com type definition }}
-  | fundef                                           :: :: fundef
+  | fundef                                             :: :: fundef
     {{ com function definition }}
-  | mapdef                                           :: :: mapdef
+  | mapdef                                             :: :: mapdef
     {{ com mapping definition }}
-  | letbind                                          :: :: val
+  | letbind                                            :: :: val
     {{ com value definition }}
-  | val_spec                                         :: :: spec
+  | val_spec                                           :: :: spec
     {{ com top-level type constraint }}
-  | fix prec num id                                  :: :: fixity
+  | fix prec num id                                    :: :: fixity
     {{ com fixity declaration }}
-  |  overload id [ id1 ; ... ; idn ]                 :: :: overload
+  |  overload id [ id1 ; ... ; idn ]                   :: :: overload
     {{ com operator overload specification }}
-  | default_spec                                     :: :: default
+  | default_spec                                       :: :: default
     {{ com default kind and type assumptions }}
-  | scattered_def                                    :: :: scattered
+  | scattered_def                                      :: :: scattered
     {{ com scattered function and type definition }}
-  | dec_spec                                         :: :: reg_dec
+  | dec_spec                                           :: :: reg_dec
     {{ com register declaration }}
-  | fundef1 .. fundefn                               :: I :: internal_mutrec
+  | constraint id ( kid1 , ... , kidn ) = n_constraint :: :: constraint
+  | fundef1 .. fundefn                                 :: I :: internal_mutrec
     {{ com internal representation of mutually recursive functions }}
 
 defs :: '' ::=
-- 
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