Move contracts DSL related stuff into a dedicated ContractsDSL.kt file, to emphasise that there is one :)

src/ContractsDSL.kt

@@ -2,6 +2,52 @@ import java.math.BigDecimal
 import java.util.*
 import kotlin.math.div
 
+/**
+ * Defines a simple domain specific language for the specificiation of financial contracts. Currently covers:
+ *
+ *  - Code for working with currencies.
+ *  - An Amount type that represents a positive quantity of a specific currency.
+ *  - A simple language extension for specifying requirements in English, along with logic to enforce them.
+ */
+
+// TODO: Look into replacing Currency and Amount with CurrencyUnit and MonetaryAmount from the javax.money API (JSR 354)
+
+// region Currencies
+///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+fun currency(code: String) = Currency.getInstance(code)
+
+val USD = currency("USD")
+val GBP = currency("GBP")
+val CHF = currency("CHF")
+
+val Int.DOLLARS: Amount get() = Amount(this * 100, USD)
+val Int.POUNDS: Amount get() = Amount(this * 100, GBP)
+val Int.SWISS_FRANCS: Amount get() = Amount(this * 100, CHF)
+val Double.DOLLARS: Amount get() = Amount((this * 100).toInt(), USD)
+val Double.POUNDS: Amount get() = Amount((this * 100).toInt(), USD)
+val Double.SWISS_FRANCS: Amount get() = Amount((this * 100).toInt(), USD)
+// endregion
+
+
+// region Requirements
+///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+object Requirements {
+    infix fun String.by(expr: Boolean) {
+        if (!expr) throw IllegalArgumentException("Failed requirement: $this")
+    }
+}
+fun requireThat(body: Requirements.() -> Unit) {
+    Requirements.body()
+}
+
+// endregion
+
+
+
+// region Amounts
+///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
 /**
  * Amount represents a positive quantity of currency, measured in pennies, which are the smallest representable units.
  * Note that "pennies" are not necessarily 1/100ths of a currency unit, but are the actual smallest amount used in
@@ -9,6 +55,9 @@ import kotlin.math.div
  *
  * Amounts of different currencies *do not mix* and attempting to add or subtract two amounts of different currencies
  * will throw [IllegalArgumentException]. Amounts may not be negative.
+ *
+ * It probably makes sense to replace this with convenience extensions over the JSR 354 MonetaryAmount interface, if
+ * that spec doesn't turn out to be too heavy (it looks fairly complicated).
  */
 data class Amount(val pennies: Int, val currency: Currency) : Comparable<Amount> {
     init {
@@ -47,3 +96,4 @@ fun Iterable<Amount>.sum() = reduce { left, right -> left + right }
 fun Iterable<Amount>.sumOrZero(currency: Currency) = if (iterator().hasNext()) sum() else Amount(0, currency)
 
 // TODO: Think about how positive-only vs positive-or-negative amounts can be represented in the type system.
+// endregion

src/TestUtils.kt

@@ -18,7 +18,7 @@ val DUMMY_PUBKEY_2 = DummyPublicKey("x2")
 val MEGA_CORP = Institution("MegaCorp", MEGA_CORP_KEY)
 val MINI_CORP = Institution("MiniCorp", MINI_CORP_KEY)
 
-val keyToCorpMap: Map<PublicKey, Institution> = mapOf(
+val TEST_KEYS_TO_CORP_MAP: Map<PublicKey, Institution> = mapOf(
         MEGA_CORP_KEY to MEGA_CORP,
         MINI_CORP_KEY to MINI_CORP
 )
@@ -52,7 +52,7 @@ data class TransactionForTest(
 ) {
     fun input(s: () -> ContractState) = inStates.add(s())
     fun output(s: () -> ContractState) = outStates.add(s())
-    fun arg(key: PublicKey, c: () -> Command) = args.add(VerifiedSignedCommand(key, keyToCorpMap[key], c()))
+    fun arg(key: PublicKey, c: () -> Command) = args.add(VerifiedSignedCommand(key, TEST_KEYS_TO_CORP_MAP[key], c()))
 
     infix fun Contract.`fails requirement`(msg: String) {
         try {

src/Utils.kt

@@ -17,35 +17,3 @@ open class OpaqueBytes(val bits: ByteArray) {
 
     override fun toString() = "[" + BaseEncoding.base16().encode(bits) + "]"
 }
-
-////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-//
-// REQUIREMENTS
-//
-// To understand how requireThat works, read the section "type safe builders" on the Kotlin website:
-//
-//   https://kotlinlang.org/docs/reference/type-safe-builders.html
-
-object Requirements {
-    infix fun String.by(expr: Boolean) {
-        if (!expr) throw IllegalArgumentException("Failed requirement: $this")
-    }
-}
-fun requireThat(body: Requirements.() -> Unit) {
-    Requirements.body()
-}
-
-////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-//
-// CURRENCIES   (convenience accessors)
-
-val USD = Currency.getInstance("USD")
-val GBP = Currency.getInstance("GBP")
-val CHF = Currency.getInstance("CHF")
-
-val Int.DOLLARS: Amount get() = Amount(this * 100, USD)
-val Int.POUNDS: Amount get() = Amount(this * 100, GBP)
-val Int.SWISS_FRANCS: Amount get() = Amount(this * 100, CHF)
-val Double.DOLLARS: Amount get() = Amount((this * 100).toInt(), USD)
-val Double.POUNDS: Amount get() = Amount((this * 100).toInt(), USD)
-val Double.SWISS_FRANCS: Amount get() = Amount((this * 100).toInt(), USD)