These are the Java APIs that might implement SLAN.
SLANPP: The SLAN Pull Parser
One might write a Pull Parser to parse SLAN with an interface like this.
public interface SlanPullParser {
public enum SlanEvent {
SYNTAX ERROR,
START_STREAM,
START_LIST,
END_LIST,
SYMBOL,
STRING,
NUMBER,
BOOLEAN_TRUE,
BOOLEAN_FALSE,
EMPTY_LIST,
END_STREAM
}
public boolean hasNext() throws IOException;
public void next() throws IOException;
public SlanEvent getEvent();
public String getString(); // value of SYMBOL or STRING
public boolean isNumber(); // if NUMBER or maybe number-like STRING
public Number getNumber(); // converts string ... if possible
public boolean isTrue(); // not BOOLEAN_FALSE or EMPTY_LIST
}
And here’s one way one might use it:
try {
while (parser.hasNext()) {
parser.next()
switch (parser.getEvent())
case START_STREAM:
...
break;
case START_LIST:
...
break;
case STRING:
String str = parser.getString();
...
break;
case SYMBOL:
String sym = parser.getSymbol();
...
break;
case BOOLEAN_TRUE:
case BOOLEAN_FALSE:
case EMPTY_LIST:
boolean flag = parser.isTrue();
...
break;
case END_LIST:
...
break;
case END_STREAM:
...
break;
default:
// ERROR ERROR ERROR
...
break;
}
}
} finally {
parser.close();
}
SLAN-List: Linked List
A parser could also simply build nested lists, just like John McCarthy used to make. The application would have to walk it just like any other parse tree.
public interface SlanValue {
enum Type { LIST, SYMBOL, STRING, NUMBER, BOOLEAN, EMPTY_LIST }
public Type getType();
public String getSymbol(); // SYMBOL (using String#intern())
public String getString(); // SYMBOL, STRING, NUMBER, BOOLEAN (Java)
public boolean isNumber(); // if NUMBER
public Number getNumber(); // NUMBER
public Boolean isTrue(); // any (true if not `#f` or `()`)
public boolean isList(); // if LIST or EMPTY_LIST
public SlanValue getHead(); // start of LIST (null if `()`)
public SlanValue getTail(); // rest of LIST (null if end of list)
public String toString(); // serializes self as SLAN
}
SLAN-B: The SLAN Builder
This interface allows one to build a SLAN document with methods that (almost) guarantee valid SLAN at the end.
The API providing a Builder assumes responsibility for writing the SLAN out to a file or URL, flushing the connection, and closing it properly.
public interface SlanBuilder {
/**
* Add a String.
* The builder will escape any characters necessary.
* @param value string
* @return this
*/
SlanBuilder addString(String value);
/**
* Add a symbol.
* If value contains characters not allowed in a symbol the
* resulting symbol will substitute '_'.
* @param value symbol
* @return this
*/
SlanBuilder addSymbol(String value);
/**
* Add a number.
* If a Double or Float, a NaN or +/-Infinity value will substitute
* the Empty List.
* @param value number
* @return this
*/
SlanBuilder addNumber(Number value);
/**
* Add a SLAN Boolean, "#t" or "#f".
* @param value boolean value
* @return this
*/
SlanBuilder addBoolean(boolean value);
/**
* Add an Empty List "()".
* @return this
*/
SlanBuilder addEmptyList();
/**
* Begin nested list.
* Subsequent calls until {@link #addListEnd} add to the nested list.
* @return a builder for the new list
*/
SlanBuilder openList();
/**
* End nested list.
* @return the builder for the parent list.
*/
SlanBuilder closeList();
/**
* Calls a procedure that builds a sublist.
* Roughly equivalent to:
* <pre>
* this.openList();
* proc.build(this);
* this.closeList();
* </pre>
*/
default SlanBuilder addList(SlanBuilder.Procedure proc) {
SlanBuilder result = this;
try {
result = this.openList();
proc.build(result);
} finally {
result = closeList();
}
return result;
}
/**
* Interface for Ruby-like method procedures.
*/
@FunctionalInterface
public interface Procedure {
void build(SlanBuilder builder);
}
}
Other Implementations
One could write SLAN parsers and emitters in any other language: C, Go, Python, Ruby, even Scheme. The APIs might vaguely resemble the ones above, adjusted for the capabilities and idioms of the language.
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