A few simple metaprogramming exercises in julia

macro_exercises_1.jl

# All expressions must evaluate to true

# Swap the first two arguments of a call expression
@swap_arguments(1 - 2) == 2 - 1

# "Invert" the operator of an expression
@invert_op(1 - 2) == 1 + 2
@invert_op(1 + 2) == 1 - 2
@invert_op(1 * 2) == 1 / 2
@invert_op(1 / 2) == 1 * 2

# Count the number of arguments to all function calls
@argcount(1 + 1) == 2
@argcount(1 + 1 - 2) == 3
@argcount((1 + 2) * (2 + 3)) == 4

# Substitute a given name by a value in a call expressions
@subs(x=>1, x+2) == 1+2
@subs(y=>2, (2y + 3y)) == 2*2 + 3*2

# Simple case statement
@case 1 begin
  1 => true
  2 => false
  3 => false
end

let x = 2
  @case x begin
    1 => false
    2 => true
    3 => false
  end
end

let x = 3
  @case x begin
    1 => false
    2 => false
    3 => true
  end
end

# A few differentiation rules:

@derivative((x) -> 1)(3)    == ((x) -> 0)(3)
@derivative((x) -> x)(3)    == ((x) -> 1)(3)
@derivative((x) -> 2x)(3)   == ((x) -> 2*1)(3)
@derivative((x) -> x+2)(3)  == ((x) -> 1+0)(3)
@derivative((x) -> x^2)(3)  == ((x) -> 2x)(3)
@derivative((x) -> 2x^2)(3) == ((x) -> 2*2x)(3)
@derivative((x) -> 2x^3)(3) == ((x) -> 2*3x^2)(3)
let n = 2
  @derivative((y) -> n*y)(3) == ((y) -> n)(3)
end