diff --git a/.idea/kotlinScripting.xml b/.idea/kotlinScripting.xml
deleted file mode 100644
index bc444dead9..0000000000
--- a/.idea/kotlinScripting.xml
+++ /dev/null
@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="KotlinScriptingSettings">
-    <option name="suppressDefinitionsCheck" value="true" />
-  </component>
-</project>
\ No newline at end of file
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/CircuitCodeGenerationBackend.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/CircuitCodeGenerationBackend.kt
index 2d675dc6d3..b503398f6a 100644
--- a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/CircuitCodeGenerationBackend.kt
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/CircuitCodeGenerationBackend.kt
@@ -2,6 +2,7 @@ package io.github.aplcornell.viaduct.backends
 
 import io.github.aplcornell.viaduct.backends.aby.ABYBackend
 import io.github.aplcornell.viaduct.backends.cleartext.CleartextBackend
+import io.github.aplcornell.viaduct.backends.commitment.CommitmentBackend
 
 /** Combines all back ends that support circuit code generation. */
-object CircuitCodeGenerationBackend : Backend by listOf(CleartextBackend, ABYBackend).unions()
+object CircuitCodeGenerationBackend : Backend by listOf(CleartextBackend, ABYBackend, CommitmentBackend).unions()
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/cleartext/CleartextCircuitCodeGenerator.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/cleartext/CleartextCircuitCodeGenerator.kt
index 02ae0f2880..26eb66167f 100644
--- a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/cleartext/CleartextCircuitCodeGenerator.kt
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/cleartext/CleartextCircuitCodeGenerator.kt
@@ -2,12 +2,19 @@ package io.github.aplcornell.viaduct.backends.cleartext
 
 import com.squareup.kotlinpoet.CodeBlock
 import com.squareup.kotlinpoet.MemberName
+import com.squareup.kotlinpoet.ParameterizedTypeName.Companion.parameterizedBy
+import com.squareup.kotlinpoet.asClassName
+import com.squareup.kotlinpoet.asTypeName
 import io.github.aplcornell.viaduct.circuitcodegeneration.AbstractCodeGenerator
 import io.github.aplcornell.viaduct.circuitcodegeneration.Argument
 import io.github.aplcornell.viaduct.circuitcodegeneration.CodeGeneratorContext
 import io.github.aplcornell.viaduct.circuitcodegeneration.UnsupportedCommunicationException
+import io.github.aplcornell.viaduct.circuitcodegeneration.kotlinType
 import io.github.aplcornell.viaduct.circuitcodegeneration.receiveExpected
 import io.github.aplcornell.viaduct.circuitcodegeneration.receiveReplicated
+import io.github.aplcornell.viaduct.circuitcodegeneration.typeTranslator
+import io.github.aplcornell.viaduct.runtime.commitment.Commitment
+import io.github.aplcornell.viaduct.runtime.commitment.Committed
 import io.github.aplcornell.viaduct.syntax.BinaryOperator
 import io.github.aplcornell.viaduct.syntax.Host
 import io.github.aplcornell.viaduct.syntax.Protocol
@@ -15,8 +22,10 @@ import io.github.aplcornell.viaduct.syntax.UnaryOperator
 import io.github.aplcornell.viaduct.syntax.circuit.OperatorNode
 import io.github.aplcornell.viaduct.syntax.operators.Maximum
 import io.github.aplcornell.viaduct.syntax.operators.Minimum
+import io.github.aplcornell.viaduct.backends.commitment.Commitment as CommitmentProtocol
 
 class CleartextCircuitCodeGenerator(context: CodeGeneratorContext) : AbstractCodeGenerator(context) {
+
     override fun operatorApplication(protocol: Protocol, op: OperatorNode, arguments: List<CodeBlock>): CodeBlock =
         when (op.operator) {
             Minimum ->
@@ -112,6 +121,128 @@ class CleartextCircuitCodeGenerator(context: CodeGeneratorContext) : AbstractCod
         }
     }
 
+    private fun createCommitment(
+        source: Protocol,
+        target: Protocol,
+        argument: Argument,
+        builder: CodeBlock.Builder,
+    ): CodeBlock {
+        require(context.host in source.hosts + target.hosts)
+        if (source !is Local) {
+            throw UnsupportedCommunicationException(source, target, argument.sourceLocation)
+        }
+        require(source.hosts.size == 1 && source.host in source.hosts)
+        require(target is CommitmentProtocol)
+        if (target.cleartextHost != source.host || target.cleartextHost in target.hashHosts) {
+            throw UnsupportedCommunicationException(source, target, argument.sourceLocation)
+        }
+
+        val argType = kotlinType(argument.type.shape, typeTranslator(argument.type.elementType.value))
+        val sendingHost = target.cleartextHost
+        val receivingHosts = target.hashHosts
+        return when (context.host) {
+            sendingHost -> {
+                val tempName1 = context.newTemporary("CommitTemp")
+                val tempName2 = context.newTemporary("CommitTemp")
+                builder.addStatement(
+                    "val %N = %T(%L)",
+                    tempName1,
+                    (Committed::class).asTypeName().parameterizedBy(argType),
+                    argument.value,
+                )
+                builder.addStatement(
+                    "val %N = %N.%M()",
+                    tempName2,
+                    tempName1,
+                    MemberName(Committed.Companion::class.asClassName(), "commitment"),
+                )
+                receivingHosts.forEach {
+                    builder.addStatement("%L", context.send(CodeBlock.of("%N", tempName2), it))
+                }
+                CodeBlock.of("%N", tempName1)
+            }
+
+            in receivingHosts -> {
+                val tempName3 = context.newTemporary("CommitTemp")
+                builder.addStatement(
+                    "val %N = %L",
+                    tempName3,
+                    context.receive((Commitment::class).asTypeName().parameterizedBy(argType), source.host),
+                )
+                CodeBlock.of("%N", tempName3)
+            }
+
+            else -> throw IllegalStateException()
+        }
+    }
+
+    private fun openCommitment(
+        source: Protocol,
+        target: Protocol,
+        argument: Argument,
+        builder: CodeBlock.Builder,
+    ): CodeBlock {
+        require(source is CommitmentProtocol)
+        if (target !is Cleartext) {
+            throw UnsupportedCommunicationException(source, target, argument.sourceLocation)
+        }
+        require(context.host in source.hosts + target.hosts)
+        if (source.hashHosts != target.hosts || source.cleartextHost in source.hashHosts) {
+            throw UnsupportedCommunicationException(source, target, argument.sourceLocation)
+        }
+
+        val argType = kotlinType(argument.type.shape, typeTranslator(argument.type.elementType.value))
+        val sendingHost = source.cleartextHost
+        val receivingHosts = target.hosts
+        return when (context.host) {
+            sendingHost -> {
+                receivingHosts.forEach {
+                    builder.addStatement("%L", context.send(argument.value, it))
+                }
+                CodeBlock.of("%L.value", argument.value)
+            }
+            in receivingHosts -> {
+                val tempName1 = context.newTemporary("CommitTemp")
+                builder.addStatement(
+                    "val %N = %L",
+                    tempName1,
+                    context.receive((Committed::class).asTypeName().parameterizedBy(argType), source.cleartextHost),
+                )
+                val tempName2 = context.newTemporary("CommitTemp")
+                builder.addStatement(
+                    "val %N = %L",
+                    tempName2,
+                    argument.value,
+                )
+                val tempName3 = context.newTemporary("CommitTemp")
+                builder.addStatement(
+                    "val %N = %N.%N(%N)",
+                    tempName3,
+                    tempName2,
+                    "open",
+                    tempName1,
+                )
+
+                val peers = receivingHosts.filter { it != context.host }
+                if (peers.isNotEmpty()) {
+                    for (host in peers) builder.addStatement("%L", context.send(CodeBlock.of(tempName3), host))
+                    builder.addStatement(
+                        "%L",
+                        receiveExpected(
+                            CodeBlock.of(tempName3),
+                            context.host,
+                            argType,
+                            peers,
+                            context,
+                        ),
+                    )
+                }
+                CodeBlock.of("%N", tempName3)
+            }
+            else -> throw IllegalStateException()
+        }
+    }
+
     override fun import(
         protocol: Protocol,
         arguments: List<Argument>,
@@ -127,6 +258,13 @@ class CleartextCircuitCodeGenerator(context: CodeGeneratorContext) : AbstractCod
                         CodeBlock.of("")
                     }
                 }
+                is CommitmentProtocol -> {
+                    if (context.host in protocol.hosts + arg.protocol.hosts) {
+                        openCommitment(arg.protocol, protocol, arg, builder)
+                    } else {
+                        CodeBlock.of("")
+                    }
+                }
 
                 else -> throw UnsupportedCommunicationException(arg.protocol, protocol, arg.sourceLocation)
             }
@@ -149,6 +287,13 @@ class CleartextCircuitCodeGenerator(context: CodeGeneratorContext) : AbstractCod
                         CodeBlock.of("")
                     }
                 }
+                is CommitmentProtocol -> {
+                    if (context.host in protocol.hosts + arg.protocol.hosts) {
+                        createCommitment(protocol, arg.protocol, arg, builder)
+                    } else {
+                        CodeBlock.of("")
+                    }
+                }
 
                 else -> throw UnsupportedCommunicationException(protocol, arg.protocol, arg.sourceLocation)
             }
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/commitment/CommitmentBackend.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/commitment/CommitmentBackend.kt
index 02f17c451d..fedd6b5b2e 100644
--- a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/commitment/CommitmentBackend.kt
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/commitment/CommitmentBackend.kt
@@ -26,5 +26,5 @@ object CommitmentBackend : Backend {
 
     override fun codeGenerator(context: CodeGeneratorContext): CodeGenerator = CommitmentDispatchCodeGenerator(context)
 
-    override fun circuitCodeGenerator(context: CircuitCodeGeneratorContext): CircuitCodeGenerator = TODO()
+    override fun circuitCodeGenerator(context: CircuitCodeGeneratorContext): CircuitCodeGenerator = CommitmentCircuitCodeGenerator(context)
 }
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/commitment/CommitmentCircuitCodeGenerator.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/commitment/CommitmentCircuitCodeGenerator.kt
new file mode 100644
index 0000000000..7cc61e184b
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/backends/commitment/CommitmentCircuitCodeGenerator.kt
@@ -0,0 +1,44 @@
+package io.github.aplcornell.viaduct.backends.commitment
+
+import com.squareup.kotlinpoet.CodeBlock
+import com.squareup.kotlinpoet.ParameterizedTypeName.Companion.parameterizedBy
+import com.squareup.kotlinpoet.TypeName
+import com.squareup.kotlinpoet.asTypeName
+import io.github.aplcornell.viaduct.circuitcodegeneration.AbstractCodeGenerator
+import io.github.aplcornell.viaduct.circuitcodegeneration.Argument
+import io.github.aplcornell.viaduct.circuitcodegeneration.CodeGeneratorContext
+import io.github.aplcornell.viaduct.circuitcodegeneration.UnsupportedCommunicationException
+import io.github.aplcornell.viaduct.circuitcodegeneration.typeTranslator
+import io.github.aplcornell.viaduct.runtime.commitment.Committed
+import io.github.aplcornell.viaduct.syntax.Protocol
+import io.github.aplcornell.viaduct.syntax.types.ValueType
+import io.github.aplcornell.viaduct.runtime.commitment.Commitment as CommitmentValue
+
+/**
+ * Backend code generator for the commitment protocol for the circuit IR.
+ *
+ * Throws an UnsupportedCommunicationException when used in an input program as a computation protocol.
+ * This is because the commitment protocol is only a storage format and not a computation protocol.
+ */
+class CommitmentCircuitCodeGenerator(context: CodeGeneratorContext) : AbstractCodeGenerator(context) {
+    override fun paramType(protocol: Protocol, sourceType: ValueType): TypeName {
+        require(protocol is Commitment)
+        return when (context.host) {
+            protocol.cleartextHost -> (Committed::class).asTypeName().parameterizedBy(typeTranslator(sourceType))
+            in protocol.hashHosts -> (CommitmentValue::class).asTypeName().parameterizedBy(typeTranslator(sourceType))
+            else -> throw IllegalStateException()
+        }
+    }
+
+    override fun storageType(protocol: Protocol, sourceType: ValueType): TypeName {
+        return super.storageType(protocol, sourceType)
+    }
+
+    override fun import(protocol: Protocol, arguments: List<Argument>): Pair<CodeBlock, List<CodeBlock>> {
+        throw UnsupportedCommunicationException(arguments.first().protocol, protocol, arguments.first().sourceLocation)
+    }
+
+    override fun export(protocol: Protocol, arguments: List<Argument>): Pair<CodeBlock, List<CodeBlock>> {
+        throw UnsupportedCommunicationException(arguments.first().protocol, protocol, arguments.first().sourceLocation)
+    }
+}
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/ArrayTypeNode.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/ArrayTypeNode.kt
new file mode 100644
index 0000000000..d66e48a18a
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/ArrayTypeNode.kt
@@ -0,0 +1,19 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.prettyprinting.Document
+import io.github.aplcornell.viaduct.prettyprinting.bracketed
+import io.github.aplcornell.viaduct.prettyprinting.plus
+import io.github.aplcornell.viaduct.syntax.Arguments
+import io.github.aplcornell.viaduct.syntax.SourceLocation
+import io.github.aplcornell.viaduct.syntax.ValueTypeNode
+
+class ArrayTypeNode(
+    val elementType: ValueTypeNode,
+    val shape: Arguments<IndexExpressionNode>,
+    override val sourceLocation: SourceLocation,
+) : Node() {
+    override val children: Iterable<Node>
+        get() = shape
+
+    override fun toDocument(): Document = elementType + shape.bracketed()
+}
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Expressions.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Expressions.kt
new file mode 100644
index 0000000000..ea1ab80285
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Expressions.kt
@@ -0,0 +1,89 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.prettyprinting.Document
+import io.github.aplcornell.viaduct.prettyprinting.bracketed
+import io.github.aplcornell.viaduct.prettyprinting.plus
+import io.github.aplcornell.viaduct.prettyprinting.times
+import io.github.aplcornell.viaduct.prettyprinting.tupled
+import io.github.aplcornell.viaduct.syntax.Arguments
+import io.github.aplcornell.viaduct.syntax.Operator
+import io.github.aplcornell.viaduct.syntax.SourceLocation
+import io.github.aplcornell.viaduct.syntax.surface.keyword
+import io.github.aplcornell.viaduct.syntax.values.Value
+
+/** A computation that produces a result. */
+sealed class ExpressionNode : Node()
+sealed class IndexExpressionNode : ExpressionNode()
+
+/** A literal constant. */
+class LiteralNode(
+    val value: Value,
+    override val sourceLocation: SourceLocation,
+) : IndexExpressionNode() {
+    override val children: Iterable<Nothing>
+        get() = listOf()
+
+    override fun toDocument(): Document = value.toDocument()
+}
+
+class ReferenceNode(
+    val name: VariableNode,
+    override val sourceLocation: SourceLocation,
+) : IndexExpressionNode() {
+    override val children: Iterable<Nothing>
+        get() = listOf()
+
+    override fun toDocument(): Document = name.toDocument()
+}
+
+class LookupNode(
+    val variable: VariableNode,
+    val indices: Arguments<IndexExpressionNode>,
+    override val sourceLocation: SourceLocation,
+) : ExpressionNode() {
+    override val children: Iterable<Node>
+        get() = indices
+
+    override fun toDocument(): Document = variable + indices.bracketed()
+}
+
+/** An n-ary operator applied to n arguments. */
+class OperatorApplicationNode(
+    val operator: OperatorNode,
+    val arguments: Arguments<ExpressionNode>,
+    override val sourceLocation: SourceLocation,
+) : ExpressionNode() {
+    override val children: Iterable<Node>
+        get() = listOf(operator) + arguments
+
+    override fun toDocument(): Document = Document("(") + operator.operator.toDocument(arguments) + ")"
+}
+
+class OperatorNode(
+    val operator: Operator,
+    override val sourceLocation: SourceLocation,
+) : Node() {
+    override val children: Iterable<Nothing>
+        get() = listOf()
+
+    override fun toDocument(): Document = Document("::$operator")
+}
+
+/**
+ * @param defaultValue to be used when the list is empty
+ * @param operator must be associative
+ */
+class ReduceNode(
+    val operator: OperatorNode,
+    val defaultValue: ExpressionNode,
+    val indices: IndexParameterNode,
+    val body: ExpressionNode,
+    override val sourceLocation: SourceLocation,
+) : ExpressionNode() {
+    override val children: Iterable<Node>
+        get() = listOf(operator, defaultValue, indices, body)
+
+    override fun toDocument(): Document {
+        return keyword("reduce") + listOf(operator, defaultValue).tupled() * "{" * indices * "->" * body * " }"
+    }
+}
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/IndexParameterNode.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/IndexParameterNode.kt
new file mode 100644
index 0000000000..299bf17dae
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/IndexParameterNode.kt
@@ -0,0 +1,16 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.prettyprinting.Document
+import io.github.aplcornell.viaduct.prettyprinting.times
+import io.github.aplcornell.viaduct.syntax.SourceLocation
+
+class IndexParameterNode(
+    override val name: VariableNode,
+    val bound: IndexExpressionNode,
+    override val sourceLocation: SourceLocation,
+) : Node(), VariableDeclarationNode {
+    override val children: Iterable<Node>
+        get() = listOf(bound)
+
+    override fun toDocument(): Document = name.toDocument() * "<" * bound
+}
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Node.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Node.kt
new file mode 100644
index 0000000000..25e3d468fa
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Node.kt
@@ -0,0 +1,7 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.attributes.TreeNode
+import io.github.aplcornell.viaduct.prettyprinting.PrettyPrintable
+import io.github.aplcornell.viaduct.syntax.HasSourceLocation
+
+sealed class Node : TreeNode<Node>, HasSourceLocation, PrettyPrintable
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Parsing.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Parsing.kt
new file mode 100644
index 0000000000..203fe3da95
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Parsing.kt
@@ -0,0 +1,27 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.parsing.ProtocolParser
+import io.github.aplcornell.viaduct.parsing.SourceFile
+import io.github.aplcornell.viaduct.parsing.defaultProtocolParsers
+import io.github.aplcornell.viaduct.syntax.Protocol
+import io.github.aplcornell.viaduct.syntax.ProtocolName
+import java_cup.runtime.ComplexSymbolFactory
+
+/** Parses [this] string and returns the AST. */
+fun String.parse(
+    path: String = "<string>",
+    protocolParsers: Map<ProtocolName, ProtocolParser<Protocol>> = defaultProtocolParsers,
+): ProgramNode {
+    return SourceFile.from(path, this).parse(protocolParsers)
+}
+
+/** Parses [this] source file to IR and returns the IR. */
+fun SourceFile.parse(
+    protocolParsers: Map<ProtocolName, ProtocolParser<Protocol>> = defaultProtocolParsers,
+): ProgramNode {
+    val symbolFactory = ComplexSymbolFactory()
+    val scanner = SourceLexer(this, symbolFactory)
+    val parser = SourceParser(scanner, symbolFactory)
+    parser.protocolParsers = protocolParsers
+    return parser.parseProgram()
+}
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/ProgramNode.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/ProgramNode.kt
new file mode 100644
index 0000000000..ffdec5516b
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/ProgramNode.kt
@@ -0,0 +1,55 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.attributes.Attribute
+import io.github.aplcornell.viaduct.attributes.Tree
+import io.github.aplcornell.viaduct.attributes.attribute
+import io.github.aplcornell.viaduct.prettyprinting.Document
+import io.github.aplcornell.viaduct.prettyprinting.concatenated
+import io.github.aplcornell.viaduct.prettyprinting.plus
+import io.github.aplcornell.viaduct.syntax.Host
+import io.github.aplcornell.viaduct.syntax.SourceLocation
+import kotlinx.collections.immutable.PersistentList
+import kotlinx.collections.immutable.toPersistentList
+
+/**
+ * The source representation of a program.
+ */
+class ProgramNode(
+    val declarations: PersistentList<TopLevelDeclarationNode>,
+    override val sourceLocation: SourceLocation,
+) : Node(), List<TopLevelDeclarationNode> by declarations {
+    constructor(declarations: List<TopLevelDeclarationNode>, sourceLocation: SourceLocation) :
+        this(declarations.toPersistentList(), sourceLocation)
+
+    override val children: Iterable<Node>
+        get() = declarations
+
+    /** A lazily constructed [Tree] instance for the program. */
+    val tree: Tree<Node, ProgramNode> by lazy { Tree(this) }
+
+    private val functionCache: Attribute<(ProgramNode) -> Any?, Any?> = attribute {
+        this.invoke(this@ProgramNode)
+    }
+
+    /**
+     * Applies [function] to this program and returns the results.
+     * The result is cached, so future calls with the same function do not evaluate [function].
+     */
+    @Suppress("UNCHECKED_CAST")
+    fun <T> cached(function: (ProgramNode) -> T): T =
+        functionCache(function) as T
+
+    val hostDeclarations: Iterable<HostDeclarationNode> =
+        declarations.filterIsInstance<HostDeclarationNode>()
+
+    val hosts: Set<Host> = hostDeclarations.map { it.name.value }.toSet()
+
+//    val circuits: Iterable<CircuitDeclarationNode> =
+//        declarations.filterIsInstance<CircuitDeclarationNode>()
+
+    val functions: Iterable<FunctionDeclarationNode> =
+        declarations.filterIsInstance<FunctionDeclarationNode>()
+
+    override fun toDocument(): Document =
+        declarations.concatenated(Document.forcedLineBreak + Document.forcedLineBreak)
+}
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Statements.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Statements.kt
new file mode 100644
index 0000000000..78c78720a1
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Statements.kt
@@ -0,0 +1,146 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.prettyprinting.Document
+import io.github.aplcornell.viaduct.prettyprinting.braced
+import io.github.aplcornell.viaduct.prettyprinting.bracketed
+import io.github.aplcornell.viaduct.prettyprinting.concatenated
+import io.github.aplcornell.viaduct.prettyprinting.joined
+import io.github.aplcornell.viaduct.prettyprinting.nested
+import io.github.aplcornell.viaduct.prettyprinting.plus
+import io.github.aplcornell.viaduct.prettyprinting.times
+import io.github.aplcornell.viaduct.prettyprinting.tupled
+import io.github.aplcornell.viaduct.syntax.Arguments
+import io.github.aplcornell.viaduct.syntax.FunctionNameNode
+import io.github.aplcornell.viaduct.syntax.HostNode
+import io.github.aplcornell.viaduct.syntax.ProtocolNode
+import io.github.aplcornell.viaduct.syntax.SourceLocation
+import io.github.aplcornell.viaduct.syntax.surface.keyword
+import kotlinx.collections.immutable.PersistentList
+import kotlinx.collections.immutable.toPersistentList
+
+/** A computation with side effects. */
+sealed class StatementNode : Node()
+
+//sealed class CircuitStatementNode : StatementNode()
+
+sealed class CommandNode : Node()
+
+/** A sequence of statements. */
+class BlockNode<Statement : StatementNode>
+private constructor(
+    val statements: PersistentList<Statement>,
+    val returnStatement: ReturnNode,
+    override val sourceLocation: SourceLocation,
+) : Node(), List<Statement> by statements {
+    constructor(statements: List<Statement>, returnStatement: ReturnNode, sourceLocation: SourceLocation) :
+        this(statements.toPersistentList(), returnStatement, sourceLocation)
+
+    override val children: Iterable<Node>
+        get() = statements + listOf(returnStatement)
+
+    override fun toDocument(): Document {
+        val statements: MutableList<Document> = (statements.map { it.toDocument() } as MutableList<Document>)
+        statements.add(returnStatement.toDocument())
+        val body: Document = statements.concatenated(separator = Document.forcedLineBreak)
+        return listOf((Document.forcedLineBreak + body).nested() + Document.forcedLineBreak).braced()
+    }
+}
+
+class ReturnNode(
+    val values: Arguments<ReferenceNode>,
+    override val sourceLocation: SourceLocation,
+) : StatementNode() {
+    override val children: Iterable<Node>
+        get() = values
+
+    override fun toDocument(): Document = keyword("return") * values.joined()
+}
+
+class LetNode(
+    val bindings: Arguments<VariableBindingNode>,
+    val command: CommandNode,
+    override val sourceLocation: SourceLocation,
+) : StatementNode() {
+    override val children: Iterable<Node>
+        get() = bindings + listOf(command)
+
+    override fun toDocument(): Document =
+        keyword("val") * bindings.joined() * "=" * command
+}
+
+class VariableBindingNode(
+    override val name: VariableNode,
+    val protocol: ProtocolNode,
+    val type: ArrayTypeNode,
+    override val sourceLocation: SourceLocation,
+) : Node(), VariableDeclarationNode {
+    override val children: Iterable<Node>
+        get() = listOf(type)
+
+    override fun toDocument(): Document =
+        name + Document("@") + protocol.value.toDocument() + Document(":") * type.toDocument()
+}
+
+class FunctionCallNode(
+    val name: FunctionNameNode,
+    val bounds: Arguments<IndexExpressionNode>,
+    val inputs: Arguments<ReferenceNode>,
+    override val sourceLocation: SourceLocation,
+) : CommandNode() {
+    override val children: Iterable<Node>
+        get() = bounds + inputs
+
+    override fun toDocument(): Document {
+        return name + bounds.joined(
+            prefix = Document("<"),
+            postfix = Document(">"),
+        ) + inputs.tupled()
+    }
+}
+
+/**
+ * An external input.
+ * @param type Type of the value to receive.
+ */
+class InputNode(
+    val type: ArrayTypeNode,
+    val host: HostNode,
+    override val sourceLocation: SourceLocation,
+) : CommandNode() {
+    override val children: Iterable<Node>
+        get() = listOf(type)
+
+    override fun toDocument(): Document = host + "." + keyword("input") + "<" + type + ">()"
+}
+
+/** An external output. */
+class OutputNode(
+    val type: ArrayTypeNode,
+    val message: ReferenceNode,
+    val host: HostNode,
+    override val sourceLocation: SourceLocation,
+) : CommandNode() {
+    override val children: Iterable<Node>
+        get() = listOf(message)
+
+    override fun toDocument(): Document = host + "." + keyword("output") + listOf(message).tupled()
+}
+
+/** A command to create a new array on a computation protocol
+ *  e.g. @Local(host = Alice) for i < 10, j < 20: a[i, j] + b[i, j]
+ *  @param protocol The computation protocol on which the array is created
+ *  @param indices The index variables and expressions to be used to create the array
+ *  @param value The value to be assigned to each element of the array
+ * */
+class ArrayCreationNode(
+    val protocol: ProtocolNode,
+    val indices: Arguments<IndexParameterNode>,
+    val value: ExpressionNode,
+    override val sourceLocation: SourceLocation,
+) : CommandNode() {
+    override val children: Iterable<Node>
+        get() = indices + listOf(value)
+
+    override fun toDocument(): Document =
+        (protocol.value.toDocument() * keyword("for") * indices.joined() + ":") * value
+}
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/TopLevelDeclarations.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/TopLevelDeclarations.kt
new file mode 100644
index 0000000000..67c417819f
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/TopLevelDeclarations.kt
@@ -0,0 +1,72 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.prettyprinting.Document
+import io.github.aplcornell.viaduct.prettyprinting.joined
+import io.github.aplcornell.viaduct.prettyprinting.plus
+import io.github.aplcornell.viaduct.prettyprinting.times
+import io.github.aplcornell.viaduct.prettyprinting.tupled
+import io.github.aplcornell.viaduct.syntax.Arguments
+import io.github.aplcornell.viaduct.syntax.FunctionNameNode
+import io.github.aplcornell.viaduct.syntax.HostNode
+import io.github.aplcornell.viaduct.syntax.ProtocolNode
+import io.github.aplcornell.viaduct.syntax.SourceLocation
+import io.github.aplcornell.viaduct.syntax.surface.keyword
+
+/** A declaration at the top level of a file. */
+sealed class TopLevelDeclarationNode : Node()
+
+/**
+ * Declaration of a participant and their authority.
+ *
+ * @param name Host name.
+ */
+class HostDeclarationNode(
+    val name: HostNode,
+    override val sourceLocation: SourceLocation,
+) : TopLevelDeclarationNode() {
+    override val children: Iterable<Nothing>
+        get() = listOf()
+
+    override fun toDocument(): Document = keyword("host") * name
+}
+
+class SizeParameterNode(
+    override val name: VariableNode,
+    override val sourceLocation: SourceLocation,
+) : Node(), VariableDeclarationNode {
+    override val children: Iterable<Nothing>
+        get() = listOf()
+
+    override fun toDocument(): Document = name.toDocument()
+}
+
+/**
+ * A parameter to a function declaration.
+ */
+class ParameterNode(
+    override val name: VariableNode,
+    val protocol: ProtocolNode,
+    val type: ArrayTypeNode,
+    override val sourceLocation: SourceLocation,
+) : Node(), VariableDeclarationNode {
+    override val children: Iterable<Node>
+        get() = listOf(type)
+
+    override fun toDocument(): Document =
+        name + Document("@") + protocol.value.toDocument() + Document(":") * type.toDocument()
+}
+
+class FunctionDeclarationNode(
+    val name: FunctionNameNode,
+    val sizes: Arguments<SizeParameterNode>,
+    val inputs: Arguments<ParameterNode>,
+    val outputs: Arguments<ArrayTypeNode>,
+    val body: BlockNode<StatementNode>,
+    override val sourceLocation: SourceLocation,
+) : TopLevelDeclarationNode() {
+    override val children: Iterable<Node>
+        get() = sizes + inputs + outputs + listOf(body)
+
+    override fun toDocument(): Document =
+        (keyword("fun") * "<" + sizes.joined() + ">") * name + inputs.tupled() * "->" * outputs.joined() * body
+}
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Variable.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Variable.kt
new file mode 100644
index 0000000000..f7f24082b0
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/Variable.kt
@@ -0,0 +1,17 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+import io.github.aplcornell.viaduct.prettyprinting.Document
+import io.github.aplcornell.viaduct.prettyprinting.styled
+import io.github.aplcornell.viaduct.syntax.Located
+import io.github.aplcornell.viaduct.syntax.Name
+import io.github.aplcornell.viaduct.syntax.VariableStyle
+
+/** A variable is a name that stands for a value or an object instance. */
+data class Variable(override val name: String) : Name {
+    override val nameCategory: String
+        get() = "variable"
+
+    override fun toDocument(): Document = Document(name).styled(VariableStyle)
+}
+
+typealias VariableNode = Located<Variable>
diff --git a/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/VariableDeclarationNode.kt b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/VariableDeclarationNode.kt
new file mode 100644
index 0000000000..e77023227e
--- /dev/null
+++ b/compiler/src/main/kotlin/io/github/aplcornell/viaduct/syntax/source/VariableDeclarationNode.kt
@@ -0,0 +1,7 @@
+package io.github.aplcornell.viaduct.syntax.source
+
+/** A node that declares a [Variable]. */
+sealed interface VariableDeclarationNode {
+    /** The variable declared by this node. */
+    val name: VariableNode
+}
diff --git a/compiler/tests/should-pass/circuit/cleartext/Commitment1.circuit b/compiler/tests/should-pass/circuit/cleartext/Commitment1.circuit
new file mode 100644
index 0000000000..a1f83781b9
--- /dev/null
+++ b/compiler/tests/should-pass/circuit/cleartext/Commitment1.circuit
@@ -0,0 +1,20 @@
+host alice
+host bob
+host chuck
+
+circuit fun <> move@Local(host = alice)(a: int[]) -> b: int[] {
+    return a
+}
+
+circuit fun <> move2@Replication(hosts = {bob, chuck})(a: int[]) -> b: int[] {
+    return a
+}
+
+fun <> main() -> {
+    val a@Local(host = alice) = alice.input<int[]>()
+    val c@Commitment(sender = alice, receivers = {bob, chuck}) = move<>(a)
+    val d@Replication(hosts = {bob, chuck}) = move2<>(c)
+    val = bob.output<int[]>(d)
+    val = chuck.output<int[]>(d)
+    return
+}
diff --git a/compiler/tests/should-pass/circuit/cleartext/Commitment2.circuit b/compiler/tests/should-pass/circuit/cleartext/Commitment2.circuit
new file mode 100644
index 0000000000..8ee265cd9b
--- /dev/null
+++ b/compiler/tests/should-pass/circuit/cleartext/Commitment2.circuit
@@ -0,0 +1,18 @@
+host alice
+host bob
+
+circuit fun <> move@Local(host = alice)(a: int[]) -> b: int[] {
+    return a
+}
+
+circuit fun <> move2@Local(host = bob)(a: int[]) -> b: int[] {
+    return a
+}
+
+fun <> main() -> {
+    val a@Local(host = alice) = alice.input<int[]>()
+    val c@Commitment(sender = alice, receivers = {bob}) = move<>(a)
+    val d@Local(host = bob) = move2<>(c)
+    val = bob.output<int[]>(d)
+    return
+}
diff --git a/examples/inputs/circuit/cleartext/Commitment1-alice.txt b/examples/inputs/circuit/cleartext/Commitment1-alice.txt
new file mode 100644
index 0000000000..7ed6ff82de
--- /dev/null
+++ b/examples/inputs/circuit/cleartext/Commitment1-alice.txt
@@ -0,0 +1 @@
+5
diff --git a/examples/inputs/circuit/cleartext/Commitment1-bob.txt b/examples/inputs/circuit/cleartext/Commitment1-bob.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/examples/inputs/circuit/cleartext/Commitment1-chuck.txt b/examples/inputs/circuit/cleartext/Commitment1-chuck.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/examples/inputs/circuit/cleartext/Commitment2-alice.txt b/examples/inputs/circuit/cleartext/Commitment2-alice.txt
new file mode 100644
index 0000000000..7ed6ff82de
--- /dev/null
+++ b/examples/inputs/circuit/cleartext/Commitment2-alice.txt
@@ -0,0 +1 @@
+5
diff --git a/examples/inputs/circuit/cleartext/Commitment2-bob.txt b/examples/inputs/circuit/cleartext/Commitment2-bob.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/examples/outputs/circuit/cleartext/Commitment1-alice.txt b/examples/outputs/circuit/cleartext/Commitment1-alice.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/examples/outputs/circuit/cleartext/Commitment1-bob.txt b/examples/outputs/circuit/cleartext/Commitment1-bob.txt
new file mode 100644
index 0000000000..7ed6ff82de
--- /dev/null
+++ b/examples/outputs/circuit/cleartext/Commitment1-bob.txt
@@ -0,0 +1 @@
+5
diff --git a/examples/outputs/circuit/cleartext/Commitment1-chuck.txt b/examples/outputs/circuit/cleartext/Commitment1-chuck.txt
new file mode 100644
index 0000000000..7ed6ff82de
--- /dev/null
+++ b/examples/outputs/circuit/cleartext/Commitment1-chuck.txt
@@ -0,0 +1 @@
+5
diff --git a/examples/outputs/circuit/cleartext/Commitment2-alice.txt b/examples/outputs/circuit/cleartext/Commitment2-alice.txt
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/examples/outputs/circuit/cleartext/Commitment2-bob.txt b/examples/outputs/circuit/cleartext/Commitment2-bob.txt
new file mode 100644
index 0000000000..7ed6ff82de
--- /dev/null
+++ b/examples/outputs/circuit/cleartext/Commitment2-bob.txt
@@ -0,0 +1 @@
+5