Smalltalk-80 character meaning/usage

Question

What is the exact meaning of these characters ←, ≡, ¬, ≠, ⌾, and ∢ and how are used in Smalltalk-80?

consider the following expressions: (taken from the smalltalk-80 source code)

1. ^self class ≡ x ≡ false
2. ^mem ◦ ¬448 ≠ 0
3. strm frame ← 15000 ⌾ frame origin y rect: 20000 ⌾ frame corner y.
4. neg ← (aStream ∢ 45 "-" ifTrue: [true] ifFalse: [aStream ∢ 21 "**¬**"]).

Note: This examples were extracted from the original Xerox Alto disks found in this link: http://bitsavers.trailing-edge.com/bits/Xerox/Alto/disk_images/

Answer 1

Sounds like this is a source file from a Xerox-internal version of Smalltalk-80. For the public release they must have replaced these "unusual" chars (which required custom font glyphs) with ASCII, only keeping ← and ↑ glyphs for the _ and ^ ASCII characters.

This is a best guess based on my experience with St76/78 (Update: confirmed by Dan Ingalls):

1. ← assignment as in var ← object. Same in St80.

2. rcvr word← arg is an alternative to word: and usually indicates assignment to a slot of the receiver (e.g. x← as in point x ← 100). St80 only allows keywords ending in a colon :.

   The parser treats ← as lower precedence so you can have keyword expressions on both sides of it. E.g.

   a foo: b ← c bar: d

   would eval c bar: d and pass the result as second argument to a's foo:← method).

3. ◦ indexing as in array◦index. St80 uses at: instead.

4. ◦← equivalent to St80's at:put: as in array◦index ← value

5. ≡ identity, like St80's ==

6. ¬ literal for negative numbers as in ¬1 for -1. The parser treated - as a binary message selector so another symbol had to be used for negative numbers literals.

7. ≠ not equal, like St80's ~=

8. ≢ not identical, like St80's ~~

9. ⌾ create a Point, like St80's @

10. ∢ match token from stream. If the next token read from stream matches the argument, it is consumed and returned. Otherwise it answers false.

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