This file tries to summarize known incompatibilities between Elpi and Teyjus.

Semantics

• ; is not a built-in and behaves differently wrt !
• unification problems outside the pattern fragment are not delayed unless one passes the (deprecated) -delay-problems-outside-pattern-fragment flag to elpi
• integers are 31 bits (25 bits in Teyjus); etc for floats ...

Syntax

• Since Elpi 1.15 the default parser does not support the infix directive
• No syntax for negative numbers: ~ 2 is the unary minus applied to 2, not the number -2. If you want to write -2, just write -2 with no space in between.
• No support for \OCTAL \OCTALOCTALOCTAL \xHEX \xHEXHEX
• Strings must not contain newlines; instead \n, \b, \t, \r, \\, \", \', "" are recognized.
• Non-associative infix/prefix/postfix behave like their associative counterparts. In particular, if @@ and @@@ are two prefix operators with precedence @@ > @@@ then (@@ @@@ @@ @@@ a) is parsed nevertheless
• Elements of lists are parsed at level 120, that is the first level used in lp-syntax.elpi after 110, the level of ,.
• i<, r+, etc. are polymorphic
• No support for x :: : type l and x = : type y.
• If a file ends (without eol) inside a comment, the parser ignores the comment (in place of returning an error). The same happens if the query is not . terminated.
• No beta-redexes in the source code.

Modules

• Module signatures are ignored.
• Elpi accumulates each file once; Teyjus does it multiple times, that is always bad (all clauses are duplicated and tried multiple times, that is rarely the expected behavior).
• Elpi understands relative paths as in accumulate "../foo": resolution of relative paths is done according to the path of the accumulating file first or, if it fails, according to the TJPATH.
• No support for import.