ExpressionPatterns Examples

macromethod-examples.jl

ematch(:(a+b = c), :(a+b = c))
ematch(:(a+b = c), :(1+2 = 3), variable=:?)
ematch(:(a+b = c), :(1+2 = 3))
ematch(:(a,b), :(b,a))
ematch(:(a::!,b), :(b,a))
ematch(:(a::!,b), :(a,a))
ematch(:(a::?+b = c::?), :(1+b = 3), variable=:?)
ematch(:(a::?+b = c::?), :(1+d = 3), variable=:?)
ematch(:(x,x), :(1,2))
ematch(:((x::&),x), :(1,2), consistency=true)
ematch(:((x::&),x), :(1,1), consistency=true)
ematch(:(1...), :(1,1,1,1))
ematch(:([1,2]...), :(1,2,1,2,1,2))
ematch(:((1,2)...), :((1,2),(1,2),(1,2)))
ematch(:(a...), :(1,2,3,4,5,6,7))
ematch(:((a::&)...), :(1,2,3,4,5,6,7), consistency=true)
ematch(:((a::&)...), :(1,1,1,1,1,1,1), consistency=true)

#same as @destruct let
@elet (x,y) = :(1,2) begin
  x + y
end
    
@elet (f(x,y)) = :(a+b) begin
  (f,x,y)
end

let ex = :(for (x,y) in [[1,2],[3,4]]
               println(x)
               println(y)
           end)

  @elet (for el in coll body... end) = ex begin
    (el, coll, body)
  end
end

let ex = :(x -> 2x + 10)
  (@destruct (x -> a*x + b) -> a)(ex)
end

name(x::Symbol) = x
@destruct name(M.m) = name(m)

@destruct function applyall((fs,xss...)...)
    map((f,xs)->:($f($(xs...))), fs, xss)
end

@destruct macro reverse_operands(f(x,y)) 
  :($f($y,$x))
end

@destruct macro for_to_map(for x in coll body... end)
    :(map($coll) do $x; $(body...) end)
end

@macromethod derivate(x -> a + b)  esc(:($x -> ($x -> $a)($x) + ($x -> $b)($x)))
@macromethod derivate(x -> a - b)  esc(:($x -> ($x -> $a)($x) - ($x -> $b)($x)))
#...
@macromethod derivate((x::&) -> x) esc(:($x -> 1))
@macromethod derivate((x::&) -> c) esc(:($x -> 0))

@macromethod polynomial_terms(a::$Symbol) [[:constant=>1, :exponent=>1]]
@macromethod polynomial_terms(a::$Number) [[:constant=>a, :exponent=>0]]
@macromethod polynomial_terms(c*(a^e))    [[:constant=>c, :exponent=>e]]
@macromethod polynomial_terms(a^e)        [[:constant=>1, :exponent=>e]]
@macromethod polynomial_terms(c*a)        [[:constant=>c, :exponent=>1]]
@macromethod polynomial_terms(a + b)      :[@polynomial_terms($a)..., @polynomial_terms($b)...]
@macromethod polynomial_terms(+(a,b...))  :[@polynomial_terms($a)..., @polynomial_terms(+($(b...)))...]
@macromethod polynomial_terms(a - b) quote
  let polyb = @polynomial_terms($b)
      for pb in polyb; pb[:constant] = -(pb[:constant])
      [@polynomial_terms($a)..., polyb...]
  end
end
@macromethod polynomial_terms(f()) []


# switch statement

function makeifs(value, casevalues, expressions)
  map(casevalues,expressions) do casevalue, expression
    :(if $value == $casevalue; $expression end)
  end
end

function applyifs(default, ifs)
  foldr(default, ifs) do ifexpr, elsexpr
    push!(ifexpr.args, quote $elsexpr end)
    ifexpr
  end
end

getdefault(maybe_default) = isempty(maybe_default)?
    :(error("no matching case in switch!")) :
     (first(maybe_default))
    
@destruct macro switch(value, begin ((case::!)(casevalues) => expressions)...
                                    ((default::!) => default)...; end)
  applyifs(getdefault(default), makeifs(value, casevalues, expressions))
end

#= usage
@switch x begin
  case(c1) => expr1
  case(c2) => expr2
  ...
  default  => defaultexpr
end
=#

reflection-examples.jl

@macromethod mm(x)[any]    1
@macromethod mm(x+y)[+]    2
@macromethod mm(x-y)[-]    3
@macromethod mm(f(x,y))[f] 4

macromethods(:mm) #=>
4-element Array{MacroMethod,1}:
 @mm(x,)[P=0, L=any]
 @mm(x + y,)[P=10, L=+]
 @mm(x - y,)[P=20, L=-]
 @mm(f(x,y),)[P=30, L=f]
=#

@mm x      #> 1
@mm x+y    #> 1
@mm x-y    #> 1
@mm f(x,y) #> 1

@prefer @mm(x+y) over @mm(x)
@mm x+y #> 2
@mm x-y #> 1

@prefer any over @mm(x)
@mm x-y    #> 3
@mm f(x,y) #> 4

@prefer f over + in (@mm)
@mm x-y #> 4

@remove_method @mm(x+y)
@mm x+y #> 4

@remove_method f from (@mm)
@mm x+y #> 1