Embedded expressions in string literals. (original) (raw)

Howard Lovatt howard.lovatt at iee.org
Wed Mar 18 18:03:51 PDT 2009

Stefan's proposal is for a dynamic binding, in particular:

String message = "You entered \{x}";

is exactly the same as:

String message = "You entered " + x;

Which in turn is the same as:

StringBuilder $message = new StringBuilder( "You entered " );
$message.append( x );
String message = $message.toString();

Therefore each time "You entered {x}" is executed, x will be re-evaluated.

-- Howard.

2009/3/19 <rssh at gradsoft.com.ua>:

I don't see your binding proposal as an improvement over what we have got for many use cases, that is not to say that it isn't valuable as an API. It is an API for string processing and therefore should be a suggested library change; not part of coin. The string literals with expressions and your API proposal would be complementary, particularly if they had similar syntax. Also see a formal proposal for embedding expressions into strings on coin, it is called Proposal: Embedded Expressions for String Statements and is from Stefan Schulz.

For implementing such proposal you need a mapping between names and values. (I. e. our binding). Now, let's think about all entities, which we have: 1. binding. 2. String before process of substituting embedding expression. 3. Process of substituting embedding expression. (I. e. syntax of mini=language inside string). Applying this 3 entities we receive: 4. String after process of substituting embedding expression.  Original Stefan proposal does not specify difference between 2 and 4. Problem, that  if (2) exists only in program text (and transformed to 4 during compilation process), than  - such transformation is possible only in static context, fixed in compile-time. This means that you can't pass such string literal to arguments, and, for example, next code snipset: int x = readX(); System.out.println("You entered {x}"); Will produce result differ, than String message = "You entered {x}"; int x = readX(); System.out.println(message); I belive, that fixing all such transformations in static context is fundamentally wrong. Ok, now let's interpret Stefan proposal (EESL) in dynamic context. But for this we need specify binging (explicit or implicit [in static context ?]) and mark process of interpretation by some function. I. e. receive all the complexity of embedding interpreted language. Fortunelly, this complexity already implemented in JSR223 interface. Embedded expressions proposal in such interpretation - just yet one syntax for embedded language. (We already have near 200 JVM languages, most of them implement javax.scripting interfaces)  Of course, we can choose language of some simple syntax be default for string expression processing - in such case, binding will just a mechanism for implementation of EESL. 2009/3/19  <rssh at gradsoft.com.ua>: Hi All,

2009/3/18  <rssh at gradsoft.com.ua>: [snip]

Complex case: Create special syntax for template processing inside strings - I guess this can be a library issue. We have jsr223. May be good ideaa is adding helper methods, which process string via choosed language interptreter, i.e. ═s.scriptEval("velocity",binding); ═.... but - from other side ═we can't receive binding between names and values automatically for now. Not sure that a library would work, can you give an example of the call you propose?

Example of such call can be: binding = new Binding(); binding.put("x",x); binding.put("y",y); """   A   B   """.evalScript("PHP",binding); If PHP is avaible via JSR223 API, then string will be evaluated to A or B. Or, if you does not like PHP, you can use velocity or java. But creating binding by hands (first 3 strings of test) kill all :( From other side, in principle compiler can generate binding for local variables automatically, so in principle it is possible to create 'magic annotation', to write code like: int someMethod(); { int x=1; int y=2; @GenerateVariableBinding Binding binding; String s = """   A   B   """.evalScript("PHP",binding); System.out.println(); } (I think about formalizing and submitting such proposal, but not sure that it is possible correct define one in short terms.)

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