Add string interpolation feature for Magic arguments.

src/main/java/io/github/spencerpark/ijava/runtime/Interpolation.java

@@ -0,0 +1,115 @@
+package io.github.spencerpark.ijava.runtime;
+
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Interpolation {
+
+    private String value;
+    private int index;
+
+    public static List<Expression> parse(String value) {
+        return new Interpolation(value).parse();
+    }
+
+    private Interpolation(String stringValue) {
+        value = stringValue;
+    }
+
+    private List<Expression> parse() {
+        List<Expression> list = new ArrayList<>();
+        StringBuilder sb = new StringBuilder();
+        int length = value.length();
+        int offset = 0;
+        for (index = 0; index < length; ++index) {
+            char c = value.charAt(index);
+            if (c == '$') {
+                Expression expr = parseExpr();
+                if (expr != null) {
+                    if (sb.length() > 0) {
+                        list.add(new Expression(sb.toString(), true));
+                        sb.setLength(0);
+                    }
+                    list.add(expr);
+                    continue;
+                }
+            }
+            sb.append(c);
+        }
+
+        if (list.isEmpty() || sb.length() > 0) {
+            list.add(new Expression(sb.toString(), true));
+        }
+        return list;
+    }
+
+    private Expression parseExpr() {
+        if (index + 1 == value.length()) {
+            return null;
+        }
+
+        if (value.charAt(index + 1) == '{') {
+            return parseBraceExpr();
+        }
+        return parseSimpleExpr();
+    }
+
+    private Expression parseBraceExpr() {
+        int length = value.length();
+        StringBuilder sb = new StringBuilder();
+        for (int pos = index + 2; pos < length; ++pos) {
+            char c = value.charAt(pos);
+            if (c != '}') {
+                sb.append(c);
+            } else {
+                if (sb.length() > 0) {
+                    index = pos;
+                    return new Expression(sb.toString(), false);
+                }
+                break;
+            }
+        }
+        return null;
+    }
+
+    private Expression parseSimpleExpr() {
+        int length = value.length();
+        StringBuilder sb = new StringBuilder();
+        for (int pos = index + 1; pos < length; pos++) {
+            char c = value.charAt(pos);
+            if (sb.length() == 0) {
+                if (c != '$' && Character.isJavaIdentifierStart(c)) {
+                    sb.append(c);
+                } else {
+                    return null;
+                }
+            } else if (c != '$' && Character.isJavaIdentifierPart(c)) {
+                sb.append(c);
+            } else {
+                break;
+            }
+            index = pos;
+        }
+        return sb.length() > 0 ? new Expression(sb.toString(), false) : null;
+    }
+
+    public static final class Expression {
+
+        private String expression;
+        private boolean constant;
+
+        Expression(String expression, boolean constant) {
+            this.expression = expression;
+            this.constant = constant;
+        }
+
+        public String getExpression() {
+            return expression;
+        }
+
+        public boolean isConstant() {
+            return constant;
+        }
+    }
+}

src/main/java/io/github/spencerpark/ijava/runtime/Magics.java

@@ -4,6 +4,7 @@
 import io.github.spencerpark.ijava.JavaKernel;
 import io.github.spencerpark.jupyter.kernel.magic.registry.UndefinedMagicException;
 
+import java.util.ArrayList;
 import java.util.List;
 
 public class Magics {
@@ -12,7 +13,11 @@ public static <T> T lineMagic(String name, List<String> args) {
 
         if (kernel != null) {
             try {
-                return kernel.getMagics().applyLineMagic(name, args);
+                List<String> realArgs = new ArrayList<>(args.size());
+                for (String arg : args) {
+                    realArgs.add(kernel.evalRaw(interpolate(arg)).toString());
+                }
+                return kernel.getMagics().applyLineMagic(name, realArgs);
             } catch (UndefinedMagicException e) {
                 throw e;
             } catch (Exception e) {
@@ -28,7 +33,12 @@ public static <T> T cellMagic(String name, List<String> args, String body) {
 
         if (kernel != null) {
             try {
-                return kernel.getMagics().applyCellMagic(name, args, body);
+                List<String> realArgs = new ArrayList<>(args.size());
+                for (String arg : args) {
+                    realArgs.add(kernel.evalRaw(interpolate(arg)).toString());
+                }
+                String realBody = kernel.evalRaw(interpolate(body)).toString();
+                return kernel.getMagics().applyCellMagic(name, realArgs, realBody);
             } catch (UndefinedMagicException e) {
                 throw e;
             } catch (Exception e) {
@@ -38,4 +48,25 @@ public static <T> T cellMagic(String name, List<String> args, String body) {
             throw new RuntimeException("No IJava kernel running");
         }
     }
+
+    private static String interpolate(String input) {
+        List<Interpolation.Expression> expressions = Interpolation.parse(input);
+        StringBuilder sb = new StringBuilder();
+        sb.append("String.format(\"");
+        StringBuilder parameters = new StringBuilder();
+        for (Interpolation.Expression expression : expressions) {
+            if (expression.isConstant()) {
+                sb.append(expression.getExpression().replace("%", "%%").replace("\n", "\\n").replace("\r", "\\r"));
+            } else {
+                if (parameters.length() == 0) {
+                    parameters.append(", ");
+                }
+                parameters.append("String.valueOf(").append(expression.getExpression()).append(')');
+                sb.append("%s");
+            }
+        }
+        sb.append('"');
+        sb.append(parameters).append(");");
+        return sb.toString();
+    }
 }