Smalltalk Syntax Cheat Sheet

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A short, one page summary of what beginners need to know about Smalltalk/X syntax and most useful code fragments.
As usual, this is only a tiny fraction of what is really awailable, and you should use the builtin class browser to find many more useful functions in the system.

This page was extracted from the "Smalltalk/X Programmers guide - Smalltalk/X Cheat Sheet".
Smalltalk/X language extensions are marked with (*).

Syntax[Bearbeiten]

Comments[Bearbeiten]

Regular comment " this is a comment " any text between double quotes
EOL-Comment (*) "/ this is an End-of-Line comment text from quote-slash to line end
Token-Comment (*) "<<END
a multiline token-comment up to
a line starting with 'END'
more commented stuff here
...
comment ends here
END 		text up to line beginning with whatever token came
after the initial "<<"

Literal Constants[Bearbeiten]

Integers 12345
-12345
Large integers 1234567890123456789012345… arbitrary number of digits
Integers with radix
(Smalltalk style) 		16rAFFE, 2r010101, 8r0777, 3r012012,
16r-AFFE, 2r-010101 		prepend the radix (base)
any radix from 2..36 is possible (i.e. 3r222 is a ternary number)
Integers with radix
(C style) (*) 		0xFEED
-0xBEAF
0b11011,-0b1100 		C/Java/JavaScript style: prepend radix indicator ('x', 'b', 'o')
One of hex, binary and octal
Floats
(IEEE double; roughly 17 digits) 		12.456
1.234e17
-6.9
-6e-10
Float pi
Float e 		called "Float", but actually hold double precision
Common constants can be referred to "by name".
Short floats
(IEEE single; roughly 8 digits) (*) 		1.234f17
-6f-10 		this is controlled by a ParserFlag (singlePrecisionFloatF), which is currently defaulted to false. Thus, by default, double precision floats are created with the 'f' exponent character.
Long floats
(IEEE quad; roughly 20 digits) (*) 		1.234q17
-6q-10 		actual precision depends on the underlying CPU
(on x86/x86_64: only 80bit)
Quad floats;
roughly 34 digits (*) 		1.234Q17
-6Q-10 		computed in software; therefore slower; this is not yet officially released.
Large floats;
roughly 60 digits (*) 		1.234QL17
-6QL-10 		computed in software; therefore slower; this is not yet officially released.
Fractions (1/3)
(17/2)
ScaledDecimals 1234.53s2 the number after the s specifies the number of digits
Characters $a
Character space
Character nl
Also: "null", "tab", "return", "bell"... 		traditionally, Smalltalk does not support any escape sequence
Common constants can be referred to "by name".
Strings 'hello' traditionally, Smalltalk does not support any escape sequence inside
Strings
(C Style) (*) 		c'hello\nworld' supports the common escape sequences, such as "\n", "\t", "\xHH"
Symbols #'hello'
#foo 		without quotes, if only alphaNumeric characters
Arrays
 #( el1 el2 ... elN ) each element is a literal constant
Byte Arrays #[ b1 b2 ... bN ] each byte-element an integer constant in 0..255
Special Number Arrays (*) #XX( v1 v2 ... vN ) XX: is one of
 'u8', 's8', 'u16', 's16', 'u32', 's32', 'u64', 's64', 'f32', 'f64'
 and each element being an integer or float constant
Immediate Inline Objects (*) #{ foo: fooValue . bar: barValue } fooValue and barValue: are constants

Lambda Blocks (Closures)[Bearbeiten]

Without argument [ expr1 . expr2 ... exprN ] multiple expressions sep'd by period.
When evaluated, the value is the value
from the last expression, exprN
One argument [ :arg |
    expr1 . expr2 ... exprN
]
Multiple arguments [ :a1 :a2 ... :aN |
    expr1 . expr2 ... exprN
]

Expressions[Bearbeiten]

Unary Expression
(without argument) 		receiver messageName receiver is itself either a constant, a lambda-block, a unary expression
or a parenthesized expression
Keyword Expression
(1 arg) 		receiver messageNamePart:argExpression whitespace between the colon and the argExpression is optional.
Keyword Expression
(any number of args) 		receiver
    messageNamePart1:argExpression1
    messageNamePart2:argExpression2
    ...
    messageNamePartN:argExpressionN
Binary Expression receiver binOP arg with binOP being any combination of special characters:
* , + , - , % , & , / , \ , | , = , < , > , ? and ,


I.e. "foo ==> 123" is the binary message "==>" sent to foo with 123 as argument.
And "foo ? 123" is the binary message "?" sent to foo with 123 as argument.

Cascade Expression
(multiple messages to the same receiver) 		receiver
    message1 ;
    message2 ;
    ...
    messageN		 the receiver expression is evaluated,
then multiple messages (separated by ";") are sent to this receiver.
Parentheses for grouping ( any expression )
Assignment variable := expression can be used as expression.
Computed Array (Brace Construct) (*) { expr1 . expr2 . ... . exprN } instantiates a new Array object with elements from the expressions.
Computed Inline Object (*) { foo: fooExpr . bar: barExpr } fooExpr and barExpr: expressions
Inline string expressions (*) e'p1{e1}p2{e2}...pN{eN}pM' syntactic sugar for:
('p1%1p2%2...pN%NpM' bindWith:e1 with:e2 ... with:eN)
where each pI is a string with possible C-escapes
and each eI is a Smalltalk expression
Array Indexing (*) coll[idx]
coll[idx1][idx2]
coll[idx1][idx2][idx3] 		syntactic sugar for:
(coll at:idx)
where coll must be an indexable collection,
and idx of compatible index type.
I.e. integer for array-like collections, hash-key for dictionaries, etc.
Up to 4 dimensions are (currently supported)
Collection instantiation (*) someClass[sz]
someClass[sz][sz]
... 		syntactic sugar for:
(someClass new:sz)
where someClass must be a collection class
I.e. Array[10] creates an empty array with 10 slots.
1, 2, 3 and 4 dimensions are supported

Remaining Syntax[Bearbeiten]

Local variables (in block or method) | var1 var2 ... varN | variable declarations must be at the beginning, before any expression.
Separating multiple expressions (sequence) expr1 . expr2 . ... exprN expressions (statements) are separated by fullstop (period) characters.
The last expression may or may not be followed by a fullstop;
if there is one, this is treated like a followup empty statement.
Return from method ^ expression returns from the enclosing method (also if inside a block-closure)

Wellknown (Common) Messages[Bearbeiten]

Conditional Execution boolExpr1 ifTrue:[ ... ] ifFalse:[ ... ] variations without true-part, without false part
and with the order reversed are available.
While-Loop
(test at top) 		[ boolExpr1 ] whileTrue:[ ... ] notice the receiver being a block.
A whileFalse: variant is also available.
Do-Loop
(test at bottom) 		[ ... ] doWhile:[ boolExpr1 ] notice the test being a block.
A doUntil: variant is also available.
For-Loop start to:stop do:[:iterVar | ... ] evaluates the block (lambda) for each value in start..stop.
Enumerating Collections collection do:[:elementVar | ... ] evaluates the block (i.e. lambda) for each element in the collection.
Evaluating a Lambda Block
  without arguments:

  with arguments:


aBlock value

aBlock value:expr1 ... value:exprN

the number of arguments must match the number expected by the lambda
(although varArg lambdas are also available)
Exception Handling [ ... ] on:Error do:[:ex | ... ] evaluates the first block;
if an error is encountered, evaluate the handler

Special 'Control Structures'[Bearbeiten]

Starting another Thread p := [ ... ] fork the code inside the block will execute in a separate thread
Creating, configuring and starting another Thread p := [ ... ]
  newProcess;
  name:'my worker';
  priority:5;
  resume 		the code inside the block will execute in a separate thread
Terminating a Thread p terminate with p referring to the thread as created by newProcess or fork
Interrupting a Thread p interruptWith:[ ... ] interrupt the thread and let it execute the given code (in its interrupt seervice)
Exception Handling [ ... ]
  on:Error do:[:ex |
    ...
  ] 		the handler will get an exception argument (ex), which contains additional information, and can be told how to deal with the error
Exception Handling - proceeding [ ... ]
  on:Error do:[:ex |
    ...
    ex proceed
  ] 		proceed, as if the error did not happen
Exception Handling - restarting [ ... ]
  on:Error do:[:ex |
    ...
    ex restart
  ] 		restart the code from the beginning (usually after the handler did some cleanup, such as lazy loading a missing file...)
Exception Handling - printing [ ... ]
  on:Error do:[:ex |
    ...
    ex description
    ...
  ] 		contains a human readable description of the error
Ensure/Unwind Protect [ ... ]
  ensure:[
  ...
  ] 		the ensure block will be evaluated in any case
Ensure/Unwind Protect [ ... ]
  ifCurtailed:[
  ...
  ] 		the ifCurtailed block will be evaluated only on a non-regular exit
(i.e. when an exception was raised, or the operation was aborted or the thread terminated)
Early exit from Loops [:exit |
  ...
  code with loop
  ...
  exit value
  ...
] valueWithExit 		the block will be left, when exit is evaluated. Often used as argument of ifTrue:, as in
cond ifTrue: exit
Queries Query
  answer:something
  do:[
    ...
    Query query
    ...
  ] 		to provide answers way down to whoever is interested.
Queries answer nil if no one is there to answer.
Queries are usually more specifically used as subclasses of Query
Notifications Notification
  handle:[
    ...
  ]
  do:[
    ...
    Notification notify:someArg
    ...
  ] 		to provide information way up to whoever is interested
Notifications are usually more specifically used as subclasses of Notification
Observers 1 foo onChange:#bla evaluate:[...].
...
foo changed:#bla 		observer with generic block to evaluate
Observers 2 foo onChangeSend:#xyz to:someone.
...
foo changed 		observer with message send
Observers 3 foo addDependent:someone.
...
foo changed 		observer with send to update method of target

Queries and Notifications can be seen as observers within the calling hierarchy (i.e. information flows up or down the calling hierarchy), whereas the dependency and anChange mechanisms are independent of the control flow (even between different threads)

Synchronization and Timers[Bearbeiten]

Timed Delay Delay waitForSeconds:n self explaining
Timed Delay Delay waitUntil:(Timestamp now + 10 seconds) self explaining
Sempaphore wait s := Semaphore new.
...
s wait.
...
s signal 		obviously, the signalling must be evaluated by another thread
Sempaphore wait with timeout s := Semaphore new.
...
s waitWithTimeout:(5 seconds).
...
s signal 		obviously, the signalling must be evaluated by another thread
Multi Sempaphore wait s1 := Semaphore new.
s2 := Semaphore new.
...
which := (s1 , s2) wait.
...
s2 signal 		wait for any of multiple semaphores
Synchronized Collections a := OrderedCollection new asSharedCollection will wrap the collection so that add/remove operations are atomic

Wellknown Globals[Bearbeiten]

Logging and Messaging Transcript - the console window
Stdout - standard output
Stderr - standard error
Stdin - standard input
Logger - redefinable logger (defaults to standard error)
Common Useful Dialogs Dialog - provides many useful utility functions for standard dialogs
eg.
Dialog warn:'message'
Dialog confirm:'question'
Dialog request:'question'
Dialog requestFilename:'question'
...

Most Wellknown Classes[Bearbeiten]

Numbers Number(abstract superclass)
Integer(integral numbers)
Float(inexact)
Fraction(exact)
Complex
Collections Array (fixed size array)
OrderedCollection, List (variable size)
SortedCollection
Set, Bag (unordered)
Dictionary (mapped collections)
BinaryTree, AVLTree
SharedQueue (shared, synchronized)
many more...
Process Handling Process (lightweight thread)
OSProcess (heavyweight OS process)
Semaphore, RecursionLock (synchronization)
Monitor, BoltLock
Delay (time delays)
Files & Streams Filename (file naming, directory access, mime type)
Stream (basic stream framework)


ReadStream,WriteStream,EncodedStream
ExternalStream, FileStream, Socket, PipeStream (OS-cmd streams)

Low Level Access OperatingSystem (OS API calls)
Smalltalk(startup, shutdown and globals)
ObjectMemory(VM access)

Examples[Bearbeiten]

exampleMethod1
    |v1 v2|

    v1 := 42.
    v2 := v1 sqrt.
    Transcript showCR: 'the root of the answer to all questions is: %1' with: v2.

using expanded strings, this can be written as: 

exampleMethod1_alternative
    |v1|

    v1 := 42.
    Transcript showCR: e'the root of the answer to all questions is: {v1 sqrt}'.

enumerating elements of an array: 

exampleMethod2
    |arr|

    arr := #( 1 2.0 'three' (4 4 4 4) ).
    arr do:[:el |
        Transcript showCR: el
    ]

enumerating elements of an array with additional index: 

exampleMethod3
    |arr|

    arr := #( 1 2.0 'three' (4 4 4 4) ).
    arr doWithIndex:[:el :idx |
        Transcript showCR: e'array element at {idx} is {el} and its class is {el class name}\n'
    ]

dialogs, string-to-number conversion, error handling: 

exampleMethod4
    |s1 nr1 s2 nr2 rslt|

    s1 := Dialog request:'Enter the first number' initialAnswer:1.
    s1 isNil ifTrue:[ ^ self ].   "/ cancelled - return from method
    s2 := Dialog request:'Enter the second number' initialAnswer:2.
    s2 isNil ifTrue:[ ^ self ].   "/ cancelled - return from method

    "/ convert; on error return from method
    nr1 := Number readFrom:s1 onError:[^ self].
    nr2 := Number readFrom:s2 onError:[^ self].

    "/ save division
    [
        rslt := nr1 / nr2
    ] on: Error do:[:ex |
        (Dialog confirm: e'Error encountered: {ex description}\nProceed with zero?')
            ifFalse:[^ self]. "/ no; return from method
        ex proceedWith:0
    ].

    Dialog information: e'the result is {rslt}'

dialogs, error handling and complex square root: 

exampleMethod4
    |s nr rslt|

    s := Dialog request:'Enter a number (may be negative)' initialAnswer:2.
    s isNil ifTrue:[ ^ self ].   "/ cancelled - return from method

    "/ convert; on error return from method
    nr := Number readFrom:s onError:[^ self].

    "/ square root; catch imaginary result
    [
        rslt := nr sqrt
    ] on: ImaginaryResultError do:[:ex |
        (Dialog confirm: e'No solution in R; want to see the complex result?')
            ifFalse:[^ self]. "/ no; return from method
        rslt := Number trapImaginary:[ nr sqrt ].
        "/ rslt is now a complex number
    ].

    Dialog information: e'the result is {rslt}'


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