Concatenation of Closures in Groovy

concat.groovy

// take a boolean evaluating closure, a result for truth and a result for false
def fn_if = { cond, tr, fa, Object... overflow ->
  if( cond() ) [ tr, *overflow ] else [ fa, *overflow ]
}

// take two parameters, and return the result of multiplying these together
def fn_mult = { a, b, Object... overflow ->
  [ a * b, *overflow ]
}

// Our input parameters
params = [ { 3 > 4 }, 'yay', 'boo', 2 ]

// Our concatenated function passes params to fn_if,
// and the result (plus any unused params) to fn_mult
def combinedFn = fn_mult << fn_if

// Call our concatenated closure
println combinedFn( *params )

// prints [ 'booboo' ]