Make :- a valid tack too

src/python/flowmetal/syntax_analyzer.py

@@ -156,12 +156,17 @@ class Analyzer(AnalyzerBase):
     """
     TACK0 = _t('⊢')
     TACK1 = _t('|-')
+    TACK2 = p.KeywordToken(":-", None, None)
     LET = _t('let')
     DO = _t('do')
     FN = _t('fn')
     LIST = _t('list')
     QUOTE = _t('quote')
 
+    @classmethod
+    def _tackp(cls, t):
+        return t in [cls.TACK0, cls.TACK1, cls.TACK2]
+
     @classmethod
     def _nows(cls, tokens):
         return [t for t in tokens if not isinstance(t, p.WhitespaceToken)]
@@ -172,7 +177,7 @@ class Analyzer(AnalyzerBase):
 
         if len(tokens) == 1:
             return cls.analyze(tokens[0]), []
-        elif tokens[1] in [cls.TACK0, cls.TACK1]:
+        elif cls._tackp(tokens[1]):
             if len(tokens) >= 3:
                 return (
                     AscribeExpr(
@@ -269,7 +274,7 @@ class Analyzer(AnalyzerBase):
             if not binding_tokens:
                 raise SyntaxError(f"Analyzing `let` at {let_token.pos}, got binding expression without subsequent value expression!")
 
-            if binding_tokens[0] in [cls.TACK0, cls.TACK1]:
+            if cls._tackp(binding_tokens[0]):
                 if len(binding_tokens) < 2:
                     raise SyntaxError(f"Analyzing `let` at {let_token.pos}, got `⊢` at {binding_tokens[0].pos} without type!")
                 bind_ascription = cls.analyze(binding_tokens[1])
@@ -311,7 +316,7 @@ class Analyzer(AnalyzerBase):
             args.append(argexpr)
 
         ascription = None
-        if tokens[1] in [cls.TACK0, cls.TACK1]:
+        if cls._tackp(tokens[1]):
             ascription = cls.analyze(tokens[2])
             tokens = tokens[2:]
         else:

test/python/flowmetal/test_syntax_analyzer.py

@@ -43,6 +43,7 @@ def test_analyze_constants(txt, exprtype):
     '(fn [] 1)',
     '(fn [] ⊢ integer? x)',
     '(fn [] x |- integer?)',
+    '(fn [] x :- integer?)',
 ])
 def test_analyze(txt):
     """Make sure that do exprs work."""