datalog
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fogfish
simplified query engine based on logic programming paradigm
`datalog:p/1` and `datalog:c/1` are pure functions that returns either data type. Existed implementation is mixed. Error returned as `{error, ...}` but success is not packages to either container. `datalog:c/1` exists.
consider the use-case: ``` t(Urn,L) :- f(Urn, "urn:rdfs:label", L), L = "Lomonosov Russia". ``` predicate `f` bind second variable to `"urn:refs:label"` but variable name unknown. The parser builds ``` #{t...
Guards supports only literals. ``` h(a,b,c,x,y) :- f(a,b,c),f(x,b,y), a != 1. ``` ``` h(a,b,c,x,y) :- f(a,b,c),f(x,b,y), a != x. ** exception error: {badmap,{error,{1,datalog_yeec, ["syntax error before: ",["x"]]}}} ```