parse¶
Parse a string
parse x parse[x]Where x is a string representing
- a well-formed q expression, returns a parse tree (V3.4 can accept newlines within the string; earlier versions cannot.)
- a function, returns the function
q)parse "1 2 3 + 5" / the list 1 2 3 is parsed as a single item
+
1 2 3
5
q)parse "{x*x}"
{x*x}Warning
Should not be used with input data over 2GB in length (0Wi). Returns domain error with this condition since 4.1 2022.04.15.
A parse tree can clarify order of execution.
q)parse "1 2 3 +/: 5 7" / Each Right has postfix syntax
(/:;+)
1 2 3
5 7
q)parse "1 2 3 +neg 5 7" / neg is applied before +
+
1 2 3
(-:;5 7)A parse tree can be executed with eval.
q)eval parse "1 2 3 +/: 5 7"
6 7 8
8 9 10Explicit definitions in .q are shown in full:
q)foo:{x+2}
q)parse "foo each til 5"
k){x'y}
`foo
(k){$[-6h=@x;!x;'`type]};5)The composition of eval after parse is essentially the q interpreter.
QSQL¶
QSQL queries are parsed to the corresponding functional form.
q)\l sp.q
q)x:parse "select part:p,qty by sup:s from sp where qty>200,p=`p1"
q)x
?
`sp
,((>;`qty;200);(=;`p;,`p1))
(,`sup)!,`s
`part`qty!`p`qty
q)eval x
sup| part qty
---| --------
s1 | p1 300
s2 | p1 300Views¶
Views are special in that they are not parsable (sensibly) with -5!x (parse).
q)eval parse"a::5"
5
q)a
5
q)views[]
`symbol$()