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# Syntax-correctness parser for Tamsin, written in Tamsin.
# Distributed under a BSD-style license; see LICENSE.

# REQUIRES lib/tamsin_scanner.tamsin

# Note that this does not produce any data as a result beyond "yes, it
# parsed" or "no, there was a syntax error".  This exists to provide a
# clean, readable grammar.  For actual use, see lib/tamsin_parser.tamsin,
# which parses a Tamsin program to an AST.

# If there is any discrepancy between the language this grammar accepts,
# and the language lib/tamsin_parser.tamsin accepts, lib/tamsin_parser.tamsin
# takes precedence.

# Note that this may contain support for some features which are not in
# the current released or pre-released version.

main = grammar using tamsin_scanner:scanner.

grammar    = {"@" & pragma & "."} &
             {module | production & "."} & eof & 'ok'.
module     = word & "{" & {production & "."} & "}".
production = word & ["(" & term & {"," & term} & ")"
                    | "[" & expr0 & "]"] & "=" & expr0.
expr0      = expr1 & {("|" | "||") & expr1}.
expr1      = expr2 & {("&" | "&&") & expr2}.
expr2      = expr3 & ["using" & prodref | "@" & texpr].
expr3      = expr4 & [("→" | "->") & variable].
expr4      = expr5 & ["/" & texpr & ["/" & term]].
expr5      = "(" & expr0 & ")"
           | "[" & expr0 & "]"
           | "{" & expr0 & "}"
           | "!" & expr5
           | "set" & variable & "=" & texpr
           | "return" & texpr
           | "fail" & texpr
           | "print" & texpr
           | terminal
           | variable & [("←" | "<-") & texpr]
           | sq_string
           | prodref & ["(" & texpr & {"," & texpr} & ")"].
texpr      = term & {"+" & term}.
term       = atom & ["(" & [term & {"," & term}] & ")"]
           | "[" & [term & {"," & term}] & ["|" & term] & "]"
           | variable.
atom       = word | sq_string.
terminal   = dq_string
           | ("«" | "<<") & texpr & ("»" | ">>").
prodref    = modref & ":" & word
           | ":" & word
           | word.
modref     = "$" | word.
pragma     = "alias" & word & word & "=" & prodref
           | "unalias" & word.

word = $:alnum.
variable = $:upper.
sq_string = $:startswith('\'').
dq_string = $:startswith('"').