Experimental pattern (quasi)quoting

syndicate/patterns.py

@@ -1,5 +1,6 @@
 from .schema import dataspacePatterns as P
 from . import Symbol, Record
+from preserves import preserve
 
 _dict = dict  ## we're about to shadow the builtin
 
@@ -10,6 +11,30 @@ def bind(p):
 
 CAPTURE = bind(_)
 
+class unquote:
+    def __init__(self, pattern):
+        self.pattern = pattern
+
+# Simple, stupid single-level quasiquotation.
+def quote(p):
+    if isinstance(p, unquote):
+        return p.pattern
+    if p.VARIANT == P.Pattern.DDiscard.VARIANT:
+        return lit(preserve(p))
+    if p.VARIANT == P.Pattern.DBind.VARIANT:
+        return rec('bind', quote(p.value.pattern))
+    if p.VARIANT == P.Pattern.DLit.VARIANT:
+        return lit(preserve(p))
+    if p.VARIANT == P.Pattern.DCompound.VARIANT:
+        p = p.value
+        if p.VARIANT == P.DCompound.rec.VARIANT:
+            return rec('rec', lit(p.label), arr(*map(quote, p.fields)))
+        if p.VARIANT == P.DCompound.arr.VARIANT:
+            return rec('arr', arr(*map(quote, p.items)))
+        if p.VARIANT == P.DCompound.dict.VARIANT:
+            return rec('dict', dict(*map(lambda kv: (kv[0], quote(kv[1])), p.entries.items())))
+    raise Exception(f'Unhandled case in quote: {repr(p)}')
+
 def lit(v):
     if isinstance(v, list) or isinstance(v, tuple):
         return arr(*map(lit, v))