Let's do this: here it is, as it is

Author: jawher

.gitignore

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+.idea
+*.iml
+target/

pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>litil</groupId>
+    <artifactId>litil</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+
+    <name>litil</name>
+    <url>http://maven.apache.org</url>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.8.2</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.ow2.asm</groupId>
+            <artifactId>asm-all</artifactId>
+            <version>4.0</version>
+        </dependency>
+
+    </dependencies>
+</project>

src/main/java/litil/TypeScope.java

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+package litil;
+
+import litil.ast.Type;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class TypeScope {
+
+    private final Map<String, Type> scope;
+    private final TypeScope parent;
+
+    private TypeScope(TypeScope parent, Map<String, Type> scope) {
+        this.parent = parent;
+        this.scope = scope;
+    }
+
+    public TypeScope(TypeScope parent) {
+        this(parent, new HashMap<String, Type>());
+    }
+
+    public TypeScope() {
+        this(null, new HashMap<String, Type>());
+    }
+
+    public void define(String name, Type type) {
+        scope.put(name, type);
+    }
+
+    public Type get(String name) {
+        Type res = scope.get(name);
+        if (res == null && parent != null) {
+            res = parent.get(name);
+        }
+        return res;
+    }
+
+    public TypeScope child() {
+        return new TypeScope(this);
+    }
+
+    @Override
+    public String toString() {
+        return scope + (parent == null ? "-|" : "->" + parent);
+    }
+}

src/main/java/litil/Utils.java

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+package litil;
+
+import java.io.PrintStream;
+
+public class Utils {
+    public static String tab(int depth) {
+        StringBuilder res = new StringBuilder("");
+        for (int i = 0; i < depth; i++) {
+            res.append("\t");
+        }
+
+        return res.toString();
+    }
+
+    public static PrintStream indenting(String pkg) {
+        return new PrintStream(System.out) {
+            @Override
+            public void println(String s) {
+                super.println(s);
+            }
+        };
+    }
+}

src/main/java/litil/ast/AstNode.java

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+package litil.ast;
+
+import litil.TypeScope;
+
+public abstract class AstNode {
+    public TypeScope scope;
+    public abstract String repr(int indent);
+
+    @Override
+    public String toString() {
+        return repr(0);
+    }
+}

src/main/java/litil/ast/DataDecl.java

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+package litil.ast;
+
+import litil.Utils;
+
+import java.util.Collections;
+import java.util.List;
+
+public class DataDecl extends Instruction {
+    public static final class TypeConstructor {
+        public final String name;
+        public final List<Type> types;
+
+        public TypeConstructor(String name, List<Type> types) {
+            this.name = name;
+            this.types = types;
+        }
+
+        public TypeConstructor(String name) {
+            this.name = name;
+            this.types = Collections.emptyList();
+        }
+    }
+
+    public final String name;
+    public final Type type;
+    public final List<Type.Variable> typesVariables;
+    public final List<TypeConstructor> typeConstructors;
+
+    public DataDecl(String name, Type type, List<Type.Variable> typesVariables, List<TypeConstructor> typeConstructors) {
+        this.name = name;
+        this.type = type;
+        this.typesVariables = typesVariables;
+        this.typeConstructors = typeConstructors;
+    }
+
+    @Override
+    public String repr(int indent) {
+        StringBuilder res = new StringBuilder(Utils.tab(indent));
+        res.append("data ").append(name);
+        for (Type.Variable typesVariable : typesVariables) {
+            res.append(typesVariable).append(" ");
+        }
+        res.append(" = ");
+        boolean first = true;
+        for (TypeConstructor typeConstructor : typeConstructors) {
+            if (first) {
+                first = false;
+            } else {
+                res.append(" | ");
+            }
+            res.append(typeConstructor.name);
+            for (Type type : typeConstructor.types) {
+                res.append(" ").append(type);
+            }
+        }
+        return res.toString();
+    }
+}

src/main/java/litil/ast/DestructuringLetBinding.java

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+package litil.ast;
+
+import litil.Utils;
+
+import java.util.List;
+
+public class DestructuringLetBinding extends Instruction {
+    public final Pattern main;
+    public final List<Pattern> args;
+    public final List<Instruction> instructions;
+
+    public DestructuringLetBinding(Pattern main, List<Pattern> args, List<Instruction> instructions) {
+        this.main = main;
+        this.args = args;
+        this.instructions = instructions;
+    }
+
+    @Override
+    public String repr(int indent) {
+        StringBuilder res = new StringBuilder(Utils.tab(indent));
+        res.append("let ");
+        res.append(main);
+
+        for (Pattern arg : args) {
+            res.append(" ").append(arg);
+        }
+        res.append(" = \n");
+        for (Instruction instruction : instructions) {
+            res.append(instruction.repr(indent + 1)).append("\n");
+        }
+        return res.toString();
+    }
+
+    @Override
+    public String toString() {
+        return repr(0);
+    }
+}

src/main/java/litil/ast/ExceptionDecl.java

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+package litil.ast;
+
+import litil.Utils;
+
+import java.util.Collections;
+import java.util.List;
+
+public class ExceptionDecl extends Instruction {
+    public final String name;
+    public final List<Type> types;
+
+    public ExceptionDecl(String name, List<Type> types) {
+        this.name = name;
+        this.types = types;
+    }
+
+    @Override
+    public String repr(int indent) {
+        StringBuilder res = new StringBuilder(Utils.tab(indent));
+        res.append("exception ").append(name);
+        for (Type t : types) {
+            res.append(" ").append(t);
+        }
+        return res.toString();
+    }
+}