fixes #1940; code breakage! stricter template evaluation

tests/template/texponential_eval.nim

@@ -0,0 +1,47 @@
+# bug #1940
+
+discard """
+  nimout: '''===
+merge (A) with (B)
+merge (A B) with (C)
+merge (A B C) with (D)
+merge (A B C D) with (E)
+merge (A B C D E) with (F)
+==='''
+"""
+
+type SqlStmt = tuple
+  sql: string
+  parts: int
+
+proc sql(q: string): SqlStmt =
+  result.sql = q
+  result.parts = 1
+
+template `&%%`(x, y: SqlStmt): SqlStmt =
+  const a = x
+  const b = y
+
+  static:
+    #echo "some merge"
+    echo "merge (", a.sql, ") with (", b.sql, ")"
+
+
+  const newSql = a.sql & " " & b.sql
+  const newParts = a.parts + b.parts
+
+  SqlStmt((sql: newSql, parts: newParts))
+
+static:
+  echo "==="
+
+let c =(sql("A") &%%
+        sql("B")) &%%
+        sql("C")  &%%
+        sql("D") &%%
+        sql("E") &%%
+        sql("F")
+echo c.sql
+
+static:
+  echo "==="