Os Welton

Hecl The Mobile Scripting Language David N. Welton [email_address]

Three Things Squishy human factors Hecl programming Hecl internals

Part I – People & Languages Dirty word: MARKETING

What drives adoption? Do more with less (Ruby/Rails) Niche (Tcl/Tk, PHP) Lowers barriers to entry (PHP, VB)

What hinders adoption? Positive network externalities of existing languages Switching costs associated with existing languages

Introducing a new language Productivity gains must be huge Or – dominate a new niche Or – make something far easier to use

Mobile Development Java J2ME Flash Lite HTML/Javascript Other scripting languages

Part II – The Language Hecl - The Mobile Scripting Language

Hecl Features Tiny – MIDP1.0 configuration fits in 64K Extremely flexible Simple Interpreted - Dynamic

Extending Extensions written in Java

Code set mainform [ form label "Hello World" code { stringitem label "Hello" text "World" cmd label "Exit" code exit type exit }] setcurrent $mainform

Commands set variablename value puts ”blah blah blah” list hash + - * / foreach while if

Words, Blocks if { > $reactor_temperature 100 } { send $warning $operators initiate_shutdown }

DSL's, oh my! every 1 minute run { if { updates? } { read_queue [ + $last_update 1] } }

proc test {name code result} { catch $code res if { eq $res $result } { ok $name } else { fail $name $res $result } }

test mytest1 { set foo 10 set foo [ + 10 $foo] } 20

Syntax command word word word word set variable [command results] $variables ”quotes interpolate $variables and [commands]” {literal block of text with ”quotes”, and whatever else you might want to include}

What you have access to textfield choice text screen gauge datefield commands permanent storage sms http

Hecl Browser Dynamic updates of applications are possible!

Part III - The Interpreter Parser Types State/variables Evaluation Exceptions

Parser Simple Hand written Lazy – doesn't care what's inside {blah blah blah ”blocks of text”}

Types Weakly typed Strings Numbers Lists Hash tables

public IntThing(int i) { val = i; } public IntThing(String s) { val = Integer.parseInt(s); } public static int get(Thing thing) throws HeclException { setIntFromAny(thing); IntThing getint = (IntThing)thing.val; return getint.val; }

Strings as middleman string number hash list string number hash list STRING

Variables Simple hash tables Created for new stack levels Some tricks for visibility in other stack levels (global, upeval commands) [set varname] == $varname

The Stack proc one {} { set a 2 puts "one $a" two puts "one $a" } proc two {} { set a 4 puts "two $a" three puts "two $a" } proc three {} { set a 6 puts "three $a" } set a 1 set b 2 puts $a one puts $a 1 one 2 two 4 three 6 two 4 one 2 1

Interp Class Interp.java Holds information about Variables Comands Exceptions

Evaluation Code transformed into a series of commands with arguments (AST) Stanza.java

Exceptions Java exceptions are thrown and caught at the 'eval' level. catch and throw commands handle exceptions at the script level

Embedding Hecl import org.hecl.*; ... Interp interp = new Interp(); new HeclFile().loadModule(interp); new org.hecl.fp.HeclFloat().loadModule(interp); new org.hecl.load.HeclLoad().loadModule(interp); HeclFile.sourceFile(interp, “a_hecl_file.hcl”); ... public void someEventHandler(Event ev) { Eval.eval(eventscript); }

Extending Hecl class IncrCmd implements Command { public void cmdCode(Interp interp, Thing[] argv) throws HeclException { int m = IntThing.get(argv[1]); int n = 1; if (argv.length > 2) { n = IntThing.get(argv[2]); } ((IntThing) argv[1].val).set(m + n); return argv[1]; } }

The Future What does Hecl mean? Very open to ideas and suggestions – few users mean lots of room for innovation

Thanks! / Contact Ilenia Wolfgang Kechel Tcl O'Reilly http://www.hecl.org [email_address]

Os Welton

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Os Welton