Update

Author: odow

src/FileFormats/LP/read.jl

@@ -133,6 +133,7 @@ const _KEYWORDS = Dict(
     _TOKEN_LESS_THAN,
     _TOKEN_EQUAL_TO,
     _TOKEN_COLON,
+    _TOKEN_IMPLIES,
     _TOKEN_NEWLINE,
     _TOKEN_UNKNOWN,
 )
@@ -270,8 +271,11 @@ function _peek_inner(state::LexerState)
             end
             return Token(_TOKEN_IDENTIFIER, val)
         elseif (op = get(_OPERATORS, c, nothing)) !== nothing
-            read(state, Char)
-            if c in ('<', '>', '=') && peek(state, Char) == '='
+            read(state, Char) # Skip c
+            if c == '-' && peek(state, Char) == '>'
+                read(state, Char)
+                return Token(_TOKEN_IMPLIES, "->")
+            elseif c in ('<', '>', '=') && peek(state, Char) == '='
                 read(state, Char)  # Allow <=, >=, and ==
             end
             return Token(op, string(c))
@@ -718,14 +722,52 @@ function _is_sos_constraint(state)
        _next_token_is(state, _TOKEN_COLON, 3)
 end
 
+function _is_indicator_constraint(state)
+    return _next_token_is(state, _TOKEN_IDENTIFIER, 1) &&
+       _next_token_is(state, _TOKEN_EQUAL_TO, 2) &&
+       _next_token_is(state, _TOKEN_NUMBER, 3) &&
+       _next_token_is(state, _TOKEN_IMPLIES, 4)
+end
+
+# INDICATOR_CONSTRAINT :=
+#   IDENTIFIER "=" "0" "->" EXPRESSION SET_SUFFIX
+#   | IDENTIFIER "=" "1" "->" EXPRESSION SET_SUFFIX
+function _parse_indicator_constraint(
+    state::LexerState,
+    cache::Cache{T},
+) where {T}
+    z = _parse_variable(state, cache)
+    _expect(read(state, Token), _TOKEN_EQUAL_TO)
+    t = read(state, Token)
+    _expect(t, _TOKEN_NUMBER)
+    indicator = if t.value == "0"
+        MOI.ACTIVATE_ON_ZERO
+    elseif t.value == "1"
+        MOI.ACTIVATE_ON_ONE
+    else
+        throw(UnexpectedToken(t))
+    end
+    _expect(read(state, Token), _TOKEN_IMPLIES)
+    f = _parse_expression(state, cache)
+    set = _parse_set_suffix(state, cache)
+    return MOI.add_constraint(
+        cache.model,
+        MOI.Utilities.operate(vcat, T, z, f),
+        MOI.Indicator{indicator}(set),
+    )
+end
+
 # CONSTRAINT :=
 #   [NAME] EXPRESSION SET_SUFFIX
 #   | [NAME] SOS_CONSTRAINT
+#   | [NAME] INDICATOR_CONSTRAINT
 function _parse_constraint(state::LexerState, cache::Cache)
     name = _parse_optional_name(state, cache)
     # Check if this is an SOS constraint
     c = if _is_sos_constraint(state)
         _parse_sos_constraint(state, cache)
+    elseif _is_indicator_constraint(state)
+        _parse_indicator_constraint(state, cache)
     else
         f = _parse_expression(state, cache)
         set = _parse_set_suffix(state, cache)

test/FileFormats/LP/LP.jl

@@ -1034,41 +1034,40 @@ function test_read_variable_bounds()
     return
 end
 
-# TODO(odow): FIXME
-# function test_read_indicator()
-#     io = IOBuffer("""
-#     minimize
-#     obj: 1 x
-#     subject to
-#     c: z = 1 -> x >= 0
-#     d: z = 0 -> x - y <= 1.2
-#     bounds
-#     x free
-#     z free
-#     binary
-#     z
-#     end
-#     """)
-#     model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_LP)
-#     read!(io, model)
-#     io = IOBuffer()
-#     write(io, model)
-#     seekstart(io)
-#     @test read(io, String) == """
-#     minimize
-#     obj: 1 x
-#     subject to
-#     d:  z = 0 -> 1 x - 1 y <= 1.2
-#     c:  z = 1 -> 1 x >= 0
-#     Bounds
-#     x free
-#     y >= 0
-#     Binary
-#     z
-#     End
-#     """
-#     return
-# end
+function test_read_indicator()
+    io = IOBuffer("""
+    minimize
+    obj: 1 x
+    subject to
+    c: z = 1 -> x >= 0
+    d: z = 0 -> x - y <= 1.2
+    bounds
+    x free
+    z free
+    binary
+    z
+    end
+    """)
+    model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_LP)
+    read!(io, model)
+    io = IOBuffer()
+    write(io, model)
+    seekstart(io)
+    @test read(io, String) == """
+    minimize
+    obj: 1 x
+    subject to
+    d:  z = 0 -> 1 x - 1 y <= 1.2
+    c:  z = 1 -> 1 x >= 0
+    Bounds
+    x free
+    y >= 0
+    Binary
+    z
+    End
+    """
+    return
+end
 
 function test_VectorAffineFunction_SOS()
     model = MOI.FileFormats.LP.Model()