Implement %macro flag

A %macro must always be fully applied. Whenever the elaborator
encounters a %macro application (except in a function LHS) it evaluates
the application and sends the result to %runElab. So:

%macro
foo : args -> Elab TT
...
def = foo a b c

is equivalent to

foo : args -> Elab TT
...
def = %runElab foo a b c

CHANGELOG.md

@@ -14,6 +14,9 @@ Language changes:
    + API defined in `Language.Reflection`, including functions for getting types
      of global names, constructors of data types, and adding new top level
      declarations
+   + Implemented `%macro` function flag, to remove the syntactic noise of
+     invoking elaborator scripts. This means the function must always
+     be fully applied, and is run under `%runElab`
 
 Changes since Idris 2 v0.1.0
 ----------------------------

src/TTImp/Elab/Ambiguity.idr

@@ -126,8 +126,13 @@ expandAmbigName mode nest env orig args (IVar fc x) exp
 
     mkTerm : Bool -> EState vars -> Name -> GlobalDef -> RawImp
     mkTerm prim est n def
-        = wrapDot prim est mode n (map (snd . snd) args)
-                  (definition def) (buildAlt (IVar fc n) args)
+        = let tm = wrapDot prim est mode n (map (snd . snd) args)
+                       (definition def) (buildAlt (IVar fc n) args) in
+              if Macro `elem` flags def
+                 then case mode of
+                           InLHS _ => tm
+                           _ => IRunElab fc (ICoerced fc tm)
+                 else tm
 
     mkAlt : Bool -> EState vars -> (Name, Int, GlobalDef) -> RawImp
     mkAlt prim est (fullname, i, gdef)

tests/idris2/reflection002/power.idr

@@ -6,5 +6,9 @@ powerFn : Nat -> TTImp
 powerFn Z = `(const 1)
 powerFn (S k) = `(\x => mult x (~(powerFn k) x))
 
+%macro
+power : Nat -> Elab TT
+power n = check (powerFn n)
+
 cube : Nat -> Nat
-cube = %runElab check (powerFn 3)
+cube = power 3